Article

A New Climate-Vegetation Equilibrium State for Tropical South America

Wiley
Geophysical Research Letters
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Abstract

The existence of multiple climate-vegetation equilibria in Tropical South America is investigated under present-day climate conditions with the use of an atmospheric general circulation model coupled to a potential vegetation model. Two stable equilibria were found. One corresponds to the current biome distribution. The second is a new equilibrium state: savannas replace eastern Amazonian forests and a semi-desert area appears in the driest portion of Northeast Brazil. If sustainable development and conservation policies were not able to halt the increasing environmental degradation in those areas, then land use changes could, per se, tip the climate-vegetation system towards this new alternative drier stable equilibrium state, with savannization of parts of Amazonia and desertification of the driest area of Northeast Brazil, and with potential adverse impacts on the rich species diversity in the former region and water resources in the latter. Pages: 2199

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... Also, the tropical forest-savanna boundaries are prone to other climate and anthropogenic-induced disturbance regimes (Sankaran et al. 2005;Staver et al. 2011b). For instance, climate change facilitated savannization in the forested areas of the Amazon region and sub-Saharan Africa due to increased atmospheric temperature, decreased annual rainfall, increased solar radiation and low humidity (Oyama and Nobre 2003;Hutyra et al. 2005;Hirota et al. 2010;Coe et al. 2013). ...
... The distance to rivers, elevation, soil types, and slope were selected as ecological factors (Hill and Hanan 2010;Zeng et al. 2014;Li et al. 2022). We selected atmospheric temperature, rainfall, and wind speed as climatic factors along seasonal variation (Oyama and Nobre 2003;Hutyra et al. 2005;Archibald et al. 2012;Hirota et al. 2010;Coe et al. 2013;Aleman et al. 2019). Lands covered with temporary features such as rock hillocks. ...
... The vegetation cover attributes of Old Oyo NationalPark, Nigeria in 1986, 2003 ...
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Savannization and de-savannization are two land cover transition processes that are yet to be understood at a local scale in sub-Saharan Africa. We studied the patterns across different ecological, anthropogenic and climatic factors to infer the trends of savannization and de-savannization in Old Oyo National Park, Nigeria. Geospatial technology and two machine learning methods were used to determine the pattern, dynamics, and importance of savannization and de-savannization with a set of thirteen eco-climatic variables. The savannized areas with total land cover masses of 934.27 km2 in 1986-2003 decreased to 901.01 km2 in 2003-2019, and vice versa for de-savannized areas. The thirteen eco-climatic variables contributed to savannization and de-savannization within the two transition intervals in varying degrees. Relevant stakeholders should employ mild burn severity to manage savannization at locations close to host communities, rivers, and roads within elevations above 450 m and low rainfall in the dry season below 6 mm.
... Due to the region's natural climatic variability, it has a lower mean annual rainfall rate and a greater temperature range [13]. Furthermore, this region has been identified as more vulnerable to climate change due to increased deforestation, global warming, and forest fires compared to the northern and western Amazon regions [19,39,50]. Hence, forest-dependent communities are most impacted by deforestation effects, mainly in these regions of the Brazilian Amazon [6,8,13,23,51]. ...
... Possible mechanisms of future "savannization" of the Amazon have been put forth by several studies [1,50,51,112,113]. The gradual process of replacing forest vegetation with savannah-like open canopy degraded ecosystems may begin as early as in the 2020-2029 decade [51], as a result of forest deforestation rates ranging between 20 and 40%, global warming above 4 • C, and forest fires [13,114]. ...
... Significant changes such as the reduction in precipitation, an increase in temperature, and the length of the dry season have already been shown in the Amazon [16,117,118]. Despite this, floristic composition during the changes to degraded savanna-like vegetation process remains poorly studied [1,50,114]. Salazar et al. (2007) note that typical tropical and sub-tropical savannah plant species would require hundreds or thousands of years to occupy the driest and hottest Amazon regions via natural migration processes [51]. ...
Article
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We review the consequences of environmental changes caused by human activities on forest products and forest-dependent communities in the Amazon region—the vast Amazonas River basin and the Guiana Shield in South America. We used the 2018 and 2021 Intergovernmental Panel on Climate Change reports and recent scientific studies to present evidence and hypotheses for changes in the ecosystem productivity and geographical distribution of plants species. We have identified species associated with highly employed forest products exhibiting reducing populations, mainly linked with deforestation and selective logging. Changes in species composition along with a decline of valuable species have been observed in the eastern, central, and southern regions of the Brazilian Amazon, suggesting accelerated biodiversity loss. Over 1 billion native trees and palms are being lost every two years, causing economic losses estimated between US$ 1–17 billion. A decrease in native plant species can be abrupt and both temporary or persistent for over 20 years, leading to reduced economic opportunities for forest-dependent communities. Science and technology investments are considered promising in implementing agroforestry systems recovering deforested and degraded lands, which could engage companies that use forest products due to supply chain advantages.
... Notable regional specificities seemed tangible in the results. For instance, signals of increasing vegetation trends reported in the African Sahel by Herrmann et al. [39] and later by Sohoulande [40] can be noticed above the 15°N as a green belt on the Africa map in Fig. 2. Decreasing vegetation trends areas noted in the tropical South America within the latitude band 0-15°S (Fig. 2) are also consistent with findings reported by Oyama and Nobre [41]. They portended an equilibrium vegetation-climate given the magnitude of changes affecting the Amazon rainforest. ...
... In the first location (i.e., Brazil), a decline of LWE (Fig. 7a) and LAI (Fig. 7b) appeared brutal after 2012 even though the precipitation data analysis indicated no significant trend. This scenario exemplifies the ongoing anthropogenic pressure on vegetation covers and water resources in the eastern region of Brazil [41,46]. However, coefficient of determination (R 2 ) estimates in Table 5 shows 54% of the variance of LAI is explained by LWE variation. ...
... However, analyses showed that reforestation/afforestation (revegetation) across the globe are not taking place in the regions affected by deforestation (vegetation loss). Paradigms outlined for areas with declining vegetation cover and water resources sustained that human-induced changes can supersede the overall connection between climate gradients, terrestrial vegetation/water resources [2,41]. Under the pivotal role of vegetation covers on the earth's energy balance and terrestrial water balance [33], the findings of this study could be considered to plan broad actions for ecosystem sustainability programs at global and regional scales. ...
Article
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Changes in the terrestrial climate and the rapid growth of the world population cause pressures on water resources and natural vegetation covers. Given the importance of these resources for the survival of both human communities and the terrestrial ecosystems, it is critical to envision research-based strategies for their preservation. However, studies that assessed changes in vegetation and freshwater resources have preferentially focused on the marginal role of human, precipitation, and temperature, while neglecting the connection with global climate gradient. Yet, a full understanding of the ongoing changes in the terrestrial vegetation and water resources is needed to develop effective strategies for preserving these resources. In an effort of contributing to the understanding of these changes, this study investigates the actual patterns in the terrestrial land water masses and vegetation covers in relation with the earth climate gradient. Especially, climate aridity indices are estimated and used to highlight climate classes. Trends analyses of monthly leaf area index and land water storage anomalies show different signals depending on the earth latitude bands. Results show 36.5% of the continental lands have experienced a decrease of water resources, but these areas do not necessarily encompass regions with decreasing trends of vegetation cover. Chi-square statistics indicated significant connections between climate classes and vegetation cover trends as well as climate classes and land water storage trends. This study concludes the global climate gradient marginally regulates the dynamics of water resources and vegetation covers. Yet, examples show human-induced changes can supersede this overall connection in certain regions of the globe.
... Recent deforestation studies in the Amazon have raised attention that points of no-return, or tipping points, are already happening Nobre, 2018, 2019), sooner than previously estimated (by 2050;IPCC, 2007). If a threshold is tipped, a chain of irreversible losses causes forest dieback, the so-called "savannization of the Amazon" (Oyama and Nobre, 2003). This term helped putting Brazil in the IPCC map, because of similar concerns about desertification in tropical Africa. ...
... Savannization and desertification were both coined by the African forest expert André Aubréville (1949). The recent appropriation to the Amazonian context occurred within the Exact sciences (Oyama and Nobre, 2003; from ideas developed in Nobre et al., 1991). Several studies already called attention to the threat the term "savannization in the Amazon" poses to savanna conservation (Walter, 2006;Alvarenga, 2007;Hecht, 2007;Kageyama and Gandara, 2008;Sawyer, 2008;Veldman and Putz, 2011;Santos, 2013;Silveira et al., 2021). ...
Article
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Words and terms evoke responses in us, independently of their original meaning. Precise language matters because terminology can affect conservation. For example, current deforestation rates put the Amazon in the spotlight of global conservation, particularly after the “savannization of the Amazon” was proposed. This term associates cleared or degraded forests with savannas, reinforcing prejudices against natural savannas. The Cerrado is the world’s largest and richest savanna, but receives less conservation attention and resources. Firstly, we showed a multisector Cerrado neglect: number of protected areas, non-governmental organizations, academic human resources, and companies were larger in the Amazon, but deforested area was proportionally smaller. Secondly, we analyzed the academic use of “savannization of the Amazon.” In all 481 studies using this term, human action was implied, and most meant that degraded Amazon does not become old-growth savanna. We propose abandoning the use of “savannization of the Amazon”, promoting the support and attention the Cerrado needs.
... About 20 years ago, modeling studies pointed to a potential Amazon dieback under climate change (White et al. 1999;Cox et al. 2000Cox et al. , 2004Cramer et al. 2001;Oyama and Nobre 2003). Up to now a substantial amount of literature has painted a complex picture with key uncertainties regarding the resilience and potential tipping points of the Amazon under global and regional environmental changes. ...
... The effects on carbon assimilation also impact the flux of water from the surface vegetation to the atmosphere through transpiration, reinforcing the moisture limitation and ultimately leading to a shift of PFTs, from predominantly tropical broadleaf trees to C4 grasses with about 30% of broadleaf tree cover, resembling savanna vegetation Cox et al. 2004). Even without acknowledging such feedbacks through coupling within ESMs, previous offline simulations support such "savannization" processes (section 22.2.2) under future scenarios of precipitation and temperature changes (Nobre et al. 1991;Oyama and Nobre 2003). Importantly, the feedbacks magnify the regional climate and vegetation response, and a long-term commitment to Amazon dieback occurs at 2°C global warming, determining an actual tipping point (4) from section 22.2 (Jones et al. 2009). ...
Chapter
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... For Amazonian ecosystems, tipping point simulations performed so far rely on both offline and coupled runs (tipping points (4) and (5) from section 22.2). Taking the inherent limitations of simulating alternative stable states into account, below we present a summary of what such models can already tell us about dieback, thresh- About 20 years ago, modeling studies pointed to a potential Amazon dieback under climate change Cox et al. 2000Cox et al. , 2004Cramer et al. 2001;Oyama and Nobre 2003). Up to now a substantial amount of literature has painted a complex picture with key uncertainties regarding the resilience and potential tipping points of the Amazon under global and regional environmental changes. ...
... The effects on carbon assimilation also impact the flux of water from the surface vegetation to the atmosphere through transpiration, reinforcing the moisture limitation and ultimately leading to a shift of PFTs, from predominantly tropical broadleaf trees to C4 grasses with about 30% of broadleaf tree cover, resembling savanna vegetation Cox et al. 2004). Even without acknowledging such feedbacks through coupling within ESMs, previous offline simulations support such "savannization" processes (section 22.2.2) under future scenarios of precipitation and temperature changes Oyama and Nobre 2003). Importantly, the feedbacks magnify the regional climate and vegetation response, and a long-term commitment to Amazon dieback occurs at 2°C global warming, determining an actual tipping point (4) from section 22.2 ). ...
Chapter
Full-text available
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... For Amazonian ecosystems, tipping point simulations performed so far rely on both offline and coupled runs (tipping points (4) and (5) from section 22.2). Taking the inherent limitations of simulating alternative stable states into account, below we present a summary of what such models can already tell us about dieback, thresh- About 20 years ago, modeling studies pointed to a potential Amazon dieback under climate change Cox et al. 2000Cox et al. , 2004Cramer et al. 2001;Oyama and Nobre 2003). Up to now a substantial amount of literature has painted a complex picture with key uncertainties regarding the resilience and potential tipping points of the Amazon under global and regional environmental changes. ...
... The effects on carbon assimilation also impact the flux of water from the surface vegetation to the atmosphere through transpiration, reinforcing the moisture limitation and ultimately leading to a shift of PFTs, from predominantly tropical broadleaf trees to C4 grasses with about 30% of broadleaf tree cover, resembling savanna vegetation Cox et al. 2004). Even without acknowledging such feedbacks through coupling within ESMs, previous offline simulations support such "savannization" processes (section 22.2.2) under future scenarios of precipitation and temperature changes Oyama and Nobre 2003). Importantly, the feedbacks magnify the regional climate and vegetation response, and a long-term commitment to Amazon dieback occurs at 2°C global warming, determining an actual tipping point (4) from section 22.2 ). ...
Chapter
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This chapter presents country-specific descriptions of human intervention in the Amazon. In general, a rapid expansion of agricultural and extractive activities, mostly for export but also for domestic markets, and to a lesser degree small scale agriculture, have led to extensive deforestation and environmental degradation without substantially improving the living conditions of the population. Government policies and the extent of State ascendancy in the area also seem to be a powerful determinant of the nature and scale of the process. Despite the common underlying international and domestic economic and political forces in the Amazon, each country has its own particularities. In the case of Colombia, the process was shaped by the guerilla presence and deteriorated after the Peace Treaty, which does not mention “deforestation” and perpetuates Colombia’s extractivist model. Ecuador’s case is representative of the link between fossil fuel extraction, environmental deterioration, and social exclusion. The case of Peru shows an Amazon perceived as a territory awaiting to be “conquered, occupied, and exploited”, subjected to an unwavering extractive and market-orientated drive. In Bolivia, contradictions between conservation and state-led development policies and business activities, which have transformed it into the second deforestation hotspot of Amazonia after Brazil, are presented. The Venezuelan Amazon is subject to rampant violence and illegal activity driven by the political geography of gold in mixed configurations of governance, with blurred boundaries between legality and illegality and prevailing negligence concerning conservation. The Guianas share low deforestation levels and lower environmental pressures, but the recent expansion of gold mining poses a serious threat. The Brazilian case presented in the previous Chapter is referenced here when comparing countries’ experienes. Conservation experiences are also included. In all cases, unsustainable extractivist models have outpaced conservation policies; however, these experiences can prove useful in the design of effective conservation policies, reduction of greenhouse gas emissions, and improvements in living conditions of Indigenous peoples and local communities.
... For Amazonian ecosystems, tipping point simulations performed so far rely on both offline and coupled runs (tipping points (4) and (5) from section 22.2). Taking the inherent limitations of simulating alternative stable states into account, below we present a summary of what such models can already tell us about dieback, thresh- About 20 years ago, modeling studies pointed to a potential Amazon dieback under climate change Cox et al. 2000Cox et al. , 2004Cramer et al. 2001;Oyama and Nobre 2003). Up to now a substantial amount of literature has painted a complex picture with key uncertainties regarding the resilience and potential tipping points of the Amazon under global and regional environmental changes. ...
... The effects on carbon assimilation also impact the flux of water from the surface vegetation to the atmosphere through transpiration, reinforcing the moisture limitation and ultimately leading to a shift of PFTs, from predominantly tropical broadleaf trees to C4 grasses with about 30% of broadleaf tree cover, resembling savanna vegetation Cox et al. 2004). Even without acknowledging such feedbacks through coupling within ESMs, previous offline simulations support such "savannization" processes (section 22.2.2) under future scenarios of precipitation and temperature changes Oyama and Nobre 2003). Importantly, the feedbacks magnify the regional climate and vegetation response, and a long-term commitment to Amazon dieback occurs at 2°C global warming, determining an actual tipping point (4) from section 22.2 ). ...
Book
Full-text available
The Science Panel for the Amazon (SPA) is an unprecedented initiative convened under the auspices of the United Nations Sustainable Development Solutions Network (SDSN). The SPA is composed of over 200 preeminent scientists and researchers from the eight Amazonian countries, French Guiana, and global partners. These experts came together to debate, analyze, and assemble the accumulated knowledge of the scientific community, Indigenous peoples, and other stakeholders that live and work in the Amazon. The Panel is inspired by the Leticia Pact for the Amazon. This is a first-of-its-kind Report which provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development. The three volumes of the final report can be downloaded from: https://www.theamazonwewant.org/amazon-assessment-report-2021/
... According to the Intergovernmental Panel on Climate Change (IPCC), global warming will also directly increase evaporation rates and the dry seasons are expected to last even longer in semiarid regions (Oyama and Nobre, 2003;IPCC, 2022). Given this scenario, the trend is that the quantity and quality of water available in these regions will be reduced, affecting aquatic biodiversity and the management of water resources in hydrographic basins. ...
Chapter
The Northeast of South America has a semiarid climate. Most of the rivers in the region are intermittent. Native freshwater organisms were selected to endure the high temperatures and long periods of water scarcity, including dryness. These fragile systems are threatened by multiple factors, such as pollution from untreated urban waters, species introductions, water withdrawal for farming, widespread damming, and climate change, which may reduce the already scarce regional precipitation. Moreover, a large transposition program with the deviation of water from the São Francisco River to several rivers in the Northeast results in the perennialization of these rivers, with the elimination of native flora and fauna and colonization by new nonnative species.
... Fire regime and biome shifts are also occurring across the world's ecosystems due to climate change [9][10][11][12][13][14] , and models project increased transformation as warming increases 4,15 . Transition can result from climate, land use and fire interactions, such as shifting tropical forest ecosystems to seasonal forests or savannahs 9,16,17 . Fire substantially impacts ecosystems and carbon stores through vegetation mortality, hydrological cycle changes and emissions of greenhouse gases, aerosols and aerosol precursors. ...
Article
Full-text available
To avoid the worst impacts of climate change, the Paris Agreement committed countries to pursue efforts to limit global warming to 1.5 °C by urgently reducing greenhouse gas emissions. However, the Paris temperature ambitions and remaining carbon budgets mostly use models that lack feedback among fire, vegetation and carbon, which are essential for understanding the future resilience of ecosystems. Here we use a coupled fire–vegetation model to explore regional impacts and feedbacks across global warming levels. We address whether the 1.5 °C goal is consistent with avoiding significant ecosystem changes when considering shifts in fire regimes. We find that the global warming level at which fire began to impact global carbon storage significantly was 1.07 °C (0.8–1.34 °C) above pre-industrial levels and conclude that fire is already playing a major role in decreasing the effectiveness of land carbon sinks. We estimate that considering fire reduces the remaining carbon budget by 25 Gt CO2 (~5%) for limiting temperature rise to 1.5 °C and 64 GtCO2 (~5%) for 2.0 °C compared to previous estimates. Whereas limiting warming to 1.5 °C is still essential for avoiding the worst impacts of climate change, in many cases, we are already reaching the point of significant change in ecosystems rich in carbon and biodiversity.
... Our results partially agreed with modelling studies which predict that aridification would result in the browning of vegetations towards more open formations, in a process of desertification (Cook and Vizy, 2008;Oliveira et al., 2021;Oyama and Nobre, 2003;Salazar et al., 2007). However, Cerrado vegetations present intense greening that is discordant with these models, which predicted a pedologically inconsistent browning (Arruda et al., 2015;Oliveira et al., 2019) of Cerrado towards Deciduous Forests and Caatinga . ...
Article
Highlights: • A readily reproductible cloud computing approach to map greenness changes • Stable (66.8%) and browning (29.1%) areas prevail in the Brazilian Semiarid • Cerrado is strongly greening and Seasonally Dry Forests are strongly browning • There is a scaled control between environmental and human factors • Well-developed paleosols are a key to decouple water supply and climate change Abstract: Increases (greening) and losses (browning) of vegetation greenness related to climatic and anthropic changes are processes well documented in the literature. However, the control exerted by predisposition factors on the response of vegetation to these changes has been little studied, and appears to be especially important in anthropized regions. The present study aimed to map greening and browning processes, as well as to characterize and analyze their distribution in heavily anthropized regions regarding two main predisposition factors: soil and vegetation types. The Brazilian Semiarid region was used as a model area, using two novel approaches: a readily reproducible cloud computing approach to map consistent greening and browning processes, and a disaggregation approach in homogeneous units of vegetation, soil and land use types. The results showed that stable greenness dominates (66.8%), but browning is more frequent (29.1%) and intense than greening (4.1%), and may be related to desertification processes in native and anthropized areas. The distribution of greening and browning processes is zonal and heterogeneous. Environmental predisposition factors, mainly the water supply capacity, regionally control the distribution of greening and browning zones. Human-environment interplays locally regulate the intensity and distribution of the processes. We defend the need of a paradigm shift in greening and browning modeling. Further studies should consider the simultaneous and balanced use of predictors related to both predisposition and changes. The need for advances in the interpretability of these models is also evident, given that current approaches fail to elucidate the regulating mechanisms of greening and browning processes.
... Outra abordagem que exige avaliar a variação de carbono na vegetação ao longo do tempo é o estudo das respostas da Caatinga às mudanças climáticas, uma vez que este bioma é apontado como susceptível às mudanças nos padrões climáticos previstos até o final do século (Seyffarth & Rodrigues, 2017). De acordo com Oyama & Nobre (2003), a redução da precipitação pluviométrica devido às mudanças climáticas combinada com os impactos de mudanças no uso da terra pode transformar parte da Caatinga em uma vegetação típica de regiões áridas. A perda de biomassa florestal reduz a capacidade do ecossistema em remover o carbono da atmosfera e, dependendo da destinação do resíduo vegetal pós-desmatamento, aumenta as emissões de gases do efeito estufa da região (PBMC, 2014). ...
Article
Full-text available
Na Caatinga, poucos estudos contabilizam os estoques aéreos de biomassa e carbono, apesar da importância destas informações para a mitigação das mudanças climáticas. Neste estudo, foram avaliados estes estoques após o intervalo de quatro anos (2011-2015) em um remanescente em Poço Verde, SE, Brasil. Adicionalmente, foi analisada a relação desses estoques com parâmetros fitossociológicos. A biomassa foi estimada por meio de equações alométricas e o carbono como a fração de 0,47 da biomassa. A comparação dos estoques e dos dados climáticos entre os períodos foi feita pelo teste t pareado; dados climáticos ainda foram comparados aos valores históricos pelo teste de Friedman. A relação da biomassa com abundância e riqueza foi avaliada por regressões lineares. Foi observado um equilíbrio temporal dos estoques aéreos de biomassa e carbono no período avaliado, provavelmente em função de condições climáticas desfavoráveis e do grau de antropização observado, que podem ter impedido crescimento desses estoques. A biomassa não apresentou relação com abundância e/ou riqueza. Os valores totais observados dos estoques de biomassa e carbono (52,8 Mg/ha e 24,8 Mg/ha, respectivamente) estão dentro da amplitude esperada para a Caatinga. A conservação do fragmento de Caatinga estudado pode contribuir localmente para o armazenamento de carbono.
... Observations have revealed that Amazon vegetation communities are vulnerable to prolonged or repeated drought, leading to increased mortality (Esquivel-Muelbert et al., 2019;Phillips et al., 2009), decreasing forest function (Botía et al., 2022;Gatti et al., 2021) and changes in vegetation structure and/or species composition (Amigo, 2020;Brando et al., 2020;Esquivel-Muelbert et al., 2019;Yang et al., 2022). Models also indicate that these droughts may trigger basin-wide ecosystem degradation (Staal et al., 2023), which can lead to a "tipping point"-an abrupt transition in ecosystem function to an alternate stable but degraded state that is difficult to reverse (Cooper et al., 2020;Hirota et al., 2021;Lovejoy & Nobre, 2019;Oyama & Nobre, 2003). Here, we ask whether water limitation of tree communities during drought-often associated with reductions in transpiration with significant feedback effects-could be a tipping point mechanism. ...
... In Brazil, the largest forest in the planet and the largest and richest savanna in the world are undergoing destruction by people with colonial strategies of land use (Pádua 2004); however, there are still many carbon stocks that, if used as carbon credits, might be vital to recede tipping points (c.f. Oyama and Nobre 2003;Nobre 2018, 2019). One obvious course of action would then be to ease the bureaucracy to credit carbon for both small and large landowners and to incentivize Brazilian companies to commit to zero carbon practices, since it is not yet mandatory in the country. ...
Chapter
The application of effective conservation strategies depends on the knowledge on how diversity is distributed in space and time, beyond to consider it also in terms of public policies and to democratize this information. Therefore, one of the main roles of tropical conservation is to understand biological distributions and declines by monitoring, estimating, and predicting environmental changes, actions that are the first step to protect the synergetic biological, environmental, and social diversities. Despite the knowledge and investment gaps found in the Neotropics, one of the most biodiverse areas in the world, a significant amount of studies has contributed to the understanding of how fruit-feeding butterfly communities are distributed, and how changes in the environment alter their structure. The fruit-feeding butterflies are long considered a good indicator group, due to the great knowledge about its biology, and its ecological characteristics. This chapter will focus on the results and patterns obtained within in situ surveys from mostly several spatial but also temporal studies with neotropical fruit-feeding butterfly communities, enhancing its use and importance in biodiversity conservation programs.
... FIGURA 4 -Variação nos anos de estudo (2001,2004,2007,2010 Já no Brasil, trabalhos alertaram sobre essas regiões que estão em processo de desertificação, causada pela mudança do uso da terra e intensificada pelas variações climáticas locais, não somente no ecossistema da Caatinga (Sampaio et al., 2003;Lima;Abreu & Ferreira, 2008;Sampaio et al., 2008;Sousa et al., 2012), mas também na Região Amazônica (Oyama & Nobre, 2003;), no Cerrado (Ab'Sáber, 1977Jackson et al., 2007) e nos Pampas (Overbeck, 2007). Nota-se que com a redução e a alteração do clima local, reduz-se, também, a pecuária em termos de cabeças no ambiente, não só de produção, como também de consumo local (Figura 4B), com o aumento da morte dos caprinos, bovinos e equinos remanescentes (Figura 4) (Castellano & Valone, 2006;Hendricks et al., 2007;Goirán et al., 2012;Kong et al. 2014). ...
Article
A região analisada é historicamente um espaço de conflitos e de uma “violência fundadora”, situada acima do médio São Francisco, entre as cidades de Ibimirim e Cabrobó (Pernambuco/Brasil). A presença desses conflitos, associada ao colapso ambiental causado pelo neoextrativismo local e ao clima árido, são fortes indícios para influenciarem a dinâmica populacional. Porém, o contrário é observado na região. A manutenção da população na região é corroborada pelo baixo valor de emigração e pelas narrativas. Por isso, variáveis ambientais e sociais foram coletadas e analisadas para avaliar se a ausência de uma dinâmica populacional é motivada por uma resistência social. Assim, o objetivo deste trabalho foi analisar o contexto ambiental e a narrativa de quem ficou no colapso da matéria-prima na Caatinga Árida pós-neo-extrativismo, onde se pôde notar que a manutenção da população na região trata-se de uma expressão da resistência social local, na interface entre parâmetros ambientais e sociais analisados. A preservação da herança familiar (patrimonialismo) foi considerada o principal destaque nas narrativas dos sertanejos.
... These forests have a narrow thermal tolerance (Perez et al., 2016), are less resistant to climate stress, and have significant exposure to new climatic conditions (Anjos & Toledo, 2018;Holmgren et al., 2013;Seddon et al., 2016). Within the eastern Amazon, due to the ongoing precipitation decrease and increasing temperature indices, a replacement of the rain forest with more open savanna-like vegetation is expected (Hilker et al., 2014;Malhi et al., 2008;Oyama & Nobre, 2003;Seidl et al., 2017). However, despite the resemblance of this vegetation to a Cerrado vegetation type, most Cerrado tree species are predicted to lose at least 50% of their current distribution by 2055 due to climate change (Siqueira & Peterson, 2003). ...
Article
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Climate change affects ecosystems in different ways. These effects are particularly worrying in the Neotropical region, where species are most vulnerable to these changes because they live closer to their thermal safety limits. Thus, establishing conservation priorities, particularly for the definition of protected areas (PAs), is a priority. However, some PA systems within the Neotropics are ineffective even under the present environmental conditions. Here, we test the effectiveness of a PA system, within an eco-tone in northern Brazil, in protecting 24 endangered bird species under current and future (RCP8.5) climatic scenarios. We used species distribution mod-eling and dispersal corridor modeling to describe the priority areas for conservation of these species. Our results indicate that several threatened bird taxa are and will potentially be protected (i.e., occur within PAs). Nonetheless, the amount of protected area is insufficient to maintain the species in the ecotone. Moreover, most taxa will probably present drastic declines in their range sizes; some are even predicted to go globally extinct soon. Thus, we highlight the location of a potentially effective system of dispersal corridors that connects PAs in the ecotone. We reinforce the need to implement public policies and raise public awareness to maintain PAs and mitigate anthropogenic effects within them, corridors, and adjacent areas, aiming to conserve the richness and diversity of these already threatened species.
... Nobre (2003) ocorre principalmente no sudeste da Amazônia, região esta que coincide com uma zona que teoricamente apresenta dois estados de equilíbrio vegetação-clima, o primeiro representado pela Floresta Ombrófila Aberta, que corresponde ao padrão de vegetação atual, e o segundo representado pela Floresta de Transição ou Contato e pelo bioma de Cerrado, como pode ser observado nas alternâncias de biomas em Rondônia. Isso tem repercussões muito importantes, já que a mudança climática pode ser um dos fatores que poderiam levar o sistema de um estado de equilíbrio para outro. ...
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Este artigo tem como objetivo contribuir para a reflexão sobre o notável avanço da Agricultura Convencional e seus impactos, além de explorar as novas alternativas oferecidas pelos sistemas agrícolas baseados na Agricultura Ecológica sustentável. A metodologia utilizada incluiu pesquisa e análise de documentos e literatura relacionada obtida em periódicos indexados. O texto aborda o contexto histórico do desenvolvimento da agricultura, conhecido como Revolução Verde, em relação às mudanças socioeconômicas, políticas e científicas de cada período. Também discute o método produtivo brasileiro, a ocupação da Amazônia e os impactos ambientais resultantes da atividade humana, além de antecipar possíveis consequências ambientais e climáticas futuras no Bioma Amazônico. Em seguida, menciona os movimentos político-ambientalistas que influenciaram a concepção de modelos sustentáveis de produção, contrapondo-se aos modelos convencionais. Esses modelos visam ao desenvolvimento rural sustentável, integrando aspectos socioeconômicos, políticos, culturais e ambientais para aprimorar a eficiência dos sistemas produtivos e a utilização responsável dos recursos naturais. Introduz o conceito de agrossistema ou agroecossistema sob a ótica da sustentabilidade, destacando seus índices e indicadores de implementação. A conclusão ressalta a necessidade de uma ação contínua e integrada dos diferentes níveis do poder público, aliada à participação efetiva da sociedade na busca por soluções para o desenvolvimento de agrossistemas sustentáveis. (PIFFER, D. M. Evolução do Estado Ecológico e a Sustentabilidade dos Agrossistemas. In: ANAIS XI Jornada Científica CEDSA: Ética e Consumo Sustentável. XI. ed. EDUFRO, 2016. v. I, p. 499-519. ISBN: 978-85-61320-16-4. Disponível em: https://cedsa.unir.br/uploads/43434343/ arquivos/Ebook_2016_XI_Jornada_CEDSA_1766416633.pdf.)
... The Caatinga, a Brazilian seasonally dry tropical forest, is one of the largest dry forests in South America (Jardim et al. 2023;Silva et al. 2019). Despite its importance, the Caatinga has been heavily affected by anthropogenic damage, resulting in significant changes in its biodiversity and distribution (Oyama and Nobre 2003;Marengo et al. 2017;Jardim et al. 2022). Worryingly, more than 10% of Caatinga areas have been subjected to intensive processes of environmental degradation, with only 1% of them being protected areas (Mariano et al. 2018;Marques et al. 2020). ...
Article
In semi-arid regions, is necessary to explore strategies to mitigate abiotic stresses such as water deficit and salinity. This study aimed to evaluate the stress tolerance capacity of three species subjected to different water regimes and salinity levels, based on dry matter production and water use efficiency (WUE). The species Handroanthus impetiginosus, Vachellia farnesiana, and Amburana cearensis were evaluated in combination with different water regimes (50%, 75%, and 100% of reference evapotranspiration – ET0) and salinity levels (0.18, 1.50, and 1.90 dS m−1). The results show that biomass accumulation increased at 50% and 75% ET0, while the WUE decreased at 100% ET0. The salinity level (1.90 dS m−1) caused reductions in leaf dry biomass (LDB), total dry biomass (TDB), LDB/TDB ratio, and WUE. The negative effects of high salinity on plant height were greater with the application of 75% ET0. The highest WUE was obtained at 50% ET0 for A. cearensis and H. impetiginosus, while V. farnesiana obtained the highest WUE at 75% ET0. A. cearensis exhibited the highest biomass accumulation (2.58 g) and WUE (0.21 g L−1). Overall, the species can tolerate drought and salinity conditions, being sensitive to high salinity concentrations during their initial growth.
... Observations have revealed that Amazon vegetation communities are vulnerable to prolonged or repeated drought, leading to increased mortality (Esquivel-Muelbert et al., 2019;Phillips et al., 2009), decreasing forest function (Botía et al., 2022;Gatti et al., 2021) and changes in vegetation structure and/or species composition (Amigo, 2020;Brando et al., 2020;Esquivel-Muelbert et al., 2019;Yang et al., 2022). Models also indicate that these droughts may trigger basin-wide ecosystem degradation (Staal et al., 2023), which can lead to a "tipping point"-an abrupt transition in ecosystem function to an alternate stable but degraded state that is difficult to reverse (Cooper et al., 2020;Hirota et al., 2021;Lovejoy & Nobre, 2019;Oyama & Nobre, 2003). Here, we ask whether water limitation of tree communities during drought-often associated with reductions in transpiration with significant feedback effects-could be a tipping point mechanism. ...
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Understanding the effects of intensification of Amazon basin hydrological cycling—manifest as increasingly frequent floods and droughts—on water and energy cycles of tropical forests is essential to meeting the challenge of predicting ecosystem responses to climate change, including forest “tipping points”. Here, we investigated the impacts of hydrological extremes on forest function using 12+ years of observations (between 2001–2020) of water and energy fluxes from eddy covariance, along with associated ecological dynamics from biometry, at the Tapajós National Forest. Measurements encompass the strong 2015–2016 El Niño drought and La Niña 2008–2009 wet events. We found that the forest responded strongly to El Niño‐Southern Oscillation (ENSO): Drought reduced water availability for evapotranspiration ( ET ) leading to large increases in sensible heat fluxes ( H ). Partitioning ET by an approach that assumes transpiration ( T ) is proportional to photosynthesis, we found that water stress‐induced reductions in canopy conductance ( G s ) drove T declines partly compensated by higher evaporation ( E ). By contrast, the abnormally wet La Niña period gave higher T and lower E , with little change in seasonal ET . Both El Niño‐Southern Oscillation (ENSO) events resulted in changes in forest structure, manifested as lower wet‐season leaf area index. However, only during El Niño 2015–2016, we observed a breakdown in the strong meteorological control of transpiration fluxes (via energy availability and atmospheric demand) because of slowing vegetation functions (via shutdown of G s and significant leaf shedding). Drought‐reduced T and G s , higher H and E , amplified by feedbacks with higher temperatures and vapor pressure deficits, signaled that forest function had crossed a threshold, from which it recovered slowly, with delay, post‐drought. Identifying such tipping point onsets (beyond which future irreversible processes may occur) at local scale is crucial for predicting basin‐scale threshold‐crossing changes in forest energy and water cycling, leading to slow‐down in forest function, potentially resulting in Amazon forests shifting into alternate degraded states.
... Like many systems in nature, several elements of the Earth system are thought to be multistable: for a given climatic forcing, they may possess multiple competing attractors that can be reached from different initial conditions [1]. Multistability has been demonstrated in rather complex physical models of the Greenland [2] and West Antarctic [3] ice sheets, the Amazon rainforest [4], the Atlantic Meridional Overturning Circulation (AMOC) [5], and even Earth as a whole [6], supported by paleoclimatic evidence for abrupt climate changes in the past [7,8]. The proposed multistability of the AMOC has been intensively studied for several decades [9,10,11] and has recently attracted renewed attention due to a suggested loss of stability over the past century seen in observation-based indicators [12]. ...
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Anticipating critical transitions in the Earth system is of great societal relevance, yet there may be intrinsic limitations to their predictability. For instance, from the theory of dynamical systems possessing multiple chaotic attractors, it is known that the asymptotic state depends sensitively on the initial condition in the proximity of a fractal basin boundary. Here, we approach the problem of final-state sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) using a conceptual climate model, composed of a slow bistable ocean coupled to a fast chaotic atmosphere. First, we explore the occurrence of long chaotic transients in the monostable regime, which can mask a loss of stability near bifurcations. In the bistable regime, we explicitly construct the chaotic saddle using the edge tracking technique. Quantifying the final-state sensitivity through the maximum Lyapunov exponent and the lifetime of the saddle, we find that the system exhibits a fractal basin boundary with almost full phase space dimension, implying vanishing predictability of the second kind near the basin boundary. Our results demonstrate the usefulness of studying non-attracting chaotic sets in the context of predicting climatic tipping points, and provide guidance for the interpretation of higher-dimensional models such as general circulation models.
... Like many systems in nature, several elements of the Earth system are thought to be multistable: for a given climatic forcing, they may possess multiple competing attractors that can be reached from different initial conditions [1]. Multistability has been demonstrated in rather complex physical models of the Greenland [2] and West Antarctic [3] ice sheets, the Amazon rainforest [4], the Atlantic Meridional Overturning Circulation (AMOC) [5], and even Earth as a whole [6], supported by paleoclimatic evidence for abrupt climate changes in the past [7,8]. The proposed multistability of the AMOC has been intensively studied for several decades [9,10,11] and has recently attracted renewed attention due to a suggested loss of stability over the past century seen in observation-based indicators [12]. ...
Preprint
Full-text available
Anticipating critical transitions in the Earth system is of great societal relevance, yet there may be intrinsic limitations to their predictability. For instance, from the theory of dynamical systems possessing multiple chaotic attractors, it is known that the asymptotic state depends sensitively on the initial condition in the proximity of a fractal basin boundary. Here, we approach the problem of final-state sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) using a conceptual climate model, composed of a slow bistable ocean coupled to a fast chaotic atmosphere. First, we explore the occurrence of long chaotic transients in the monostable regime, which can mask a loss of stability near bifurcations. In the bistable regime, we explicitly construct the chaotic saddle using the edge tracking technique. Quantifying the final-state sensitivity through the maximum Lyapunov exponent and the lifetime of the saddle, we find that the system exhibits a fractal basin boundary with almost full phase space dimension, implying vanishing predictability of the second kind near the basin boundary. Our results demonstrate the usefulness of studying non-attracting chaotic sets in the context of predicting climatic tipping points, and provide guidance for the interpretation of higher-dimensional models such as general circulation models.
... A comparison between present and future simulations of hydrologic stress shows that floodplain forests of the Amazonas, Madeira, and Upper Negro Rivers, recognized as some of the most diverse floodplain forests in the world, with a high level of endemism (21), will likely be affected. This differs from the prevalent understanding that forest loss from a warming climate will be mostly restricted to eastern and southern Amazônia (40)(41)(42)(43)(44), with some also pointing to higher risk for forests on the eastern slopes of the Andes (45). Accounting for double stress suggests that vegetation shifts can penetrate much deeper into the heart of Amazônia Forest, affecting 4,000,000 km 2 of forest (~1.4%) through tropical South America. ...
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Forest–savanna boundaries are ecotones that support complex ecosystem functions and are sensitive to biotic/abiotic perturbations. What drives their distribution today and how it may shift in the future are open questions. Feedbacks among climate, fire, herbivory, and land use are known drivers. Here, we show that alternating seasonal drought and waterlogging stress favors the dominance of savanna-like ecosystems over forests. We track the seasonal water-table depth as an indicator of water stress when too deep and oxygen stress when too shallow and map forest/savanna occurrence within this double-stress space in the neotropics. We find that under a given annual precipitation, savannas are favored in landscape positions experiencing double stress, which is more common as the dry season strengthens (climate driver) but only found in waterlogged lowlands (terrain driver). We further show that hydrological changes at the end of the century may expose some flooded forests to savanna expansion, affecting biodiversity and soil carbon storage. Our results highlight the importance of land hydrology in understanding/predicting forest–savanna transitions in a changing world.
... 2. Oyama et al. (2003), em artigo publicado no periódico "Geophysical Research Letters" o artigo "A new climate-vegetation equilibrium state for Tropical South America" e alcançaram a métrica de segundo artigo mais citado dentre os pesquisados para a concepção deste artigo. Este artigo trata da existência de múltiplos sistemas de equilíbrios em relação ao binômio clima-vegetação na América do Sul Tropical, principalmente, dois equilíbrios estáveis foram encontrados: (1) distribuição dos biomas e (2) um novo equilíbrio entre as áreas úmidas do país e as áreas semiáridas do Nordeste brasileiro. ...
... Estudos de impactos das mudanças climáticas na estabilidade dos biomas brasileiros (OYAMA, NOBRE, 2003), revelam que o bioma Caatinga está entre os mais vulneráveis num cenário de aumento das temperaturas globais, o que coloca a região Nordeste em alerta, uma vez que os efeitos das mudanças climáticas representam mais um fator diante da pressão de origem antrópica à desertificação (OYAMA, NOBRE, 2004). ...
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Com esse artigo vislumbram-se as possibilidades de ganhos com a produção de energia fotovoltaica (solar), em consórcio com a produção de alimentos e mudas de reflorestamento (Spondias tuberosa), num sistema denominado “agrovoltaico”. Há ainda o tratamento e reutilização de águas cinzas e negras para produzir água de qualidade para irrigação para atender a produção de mudas e mitigar poluição. Esta iniciativa já qualificou mais de 700 pessoas no manejo dessas tecnologias. Ao descrever essa alternativa produtiva, adaptada às áreas de clima semiárido, busca-se indicar uma alternativa que supere o modelo da produção tradicional de criação de animais e policultura de baixa eficiência. São alternativas econômicas sem um vínculo com sistemas produtivos ancorados em oferta de água abundante e que, ao mesmo tempo, buscam interação com o Sistema Inovativo Regional - SIR, de forma a responder às carências produtivas regionais, em particular as de emprego e renda.
... A floresta seria substituída com um tipo de vegetação parecido com o cerrado, por meio da savanização. Até 60% da floresta amazônica no Brasil poderia ser transformado em cerrado pelo processo de savanização (Oyama & Nobre, 2003). ...
Book
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Fearnside, P.M. (ed.) 2022. Destruição e Conservação da Floresta Amazônica, Vol. 1. Editora do INPA, Manaus. 356 pp. https://bit.ly/3Bw8lnU
... However, human-induced impacts and climatic extremes are increasingly threatening the forest's integrity and the services it provides (3,4). Furthermore, forest changes might not be gradual, but could be rather abrupt due to nonlinear interactions, as suggested by simulation studies (5,6), databased approaches (7,8), conceptual models (9)(10)(11), and long-term experiments (12,13). Therefore, parts of the Amazon rainforest may be bistable, meaning that they could tip to an alternative state of low tree cover. ...
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Tipping elements are nonlinear subsystems of the Earth system that have the potential to abruptly shift to another state if environmental change occurs close to a critical threshold with large consequences for human societies and ecosystems. Among these tipping elements may be the Amazon rainforest, which has been undergoing intensive anthropogenic activities and increasingly frequent droughts. Here, we assess how extreme deviations from climatological rainfall regimes may cause local forest collapse that cascades through the coupled forest–climate system. We develop a conceptual dynamic network model to isolate and uncover the role of atmospheric moisture recycling in such tipping cascades. We account for heterogeneity in critical thresholds of the forest caused by adaptation to local climatic conditions. Our results reveal that, despite this adaptation, a future climate characterized by permanent drought conditions could trigger a transition to an open canopy state particularly in the southern Amazon. The loss of atmospheric moisture recycling contributes to one-third of the tipping events. Thus, by exceeding local thresholds in forest adaptive capacity, local climate change impacts may propagate to other regions of the Amazon basin, causing a risk of forest shifts even in regions where critical thresholds have not been crossed locally.
... A exploração do espaço territorial da Caatinga, por meio do pastoreio extensivo e conversão de ambientes naturais florestais em agrícolas intensificam a pressão sobre a região mais vulnerável aos efeitos promovidos pela desertificação de todo o país, suscetível ao cenário de aumento das temperaturas globais devido as mudanças climáticas -uma vez que o aumento da temperatura aliado à supressão da vegetação favorece a ocorrência de aridização e desertificação [17][18][19]. Além disso, o decréscimo de áreas de Caatinga resulta em perda de espécies endêmicas e produtos e serviços ecossistêmicos, como, por exemplo, a restauração da fertilidade, proteção do solo, produção de água e de produtos florestais como lenha, madeira e forragem [20]. O percentual de espécies endêmicas à Caatinga varia de 6% entre os mamíferos a 52,9% entre os peixes [21]. ...
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A observação multitemporal das alterações na paisagem, que afetam a biodiversidade e os serviços ecossistêmicos, podem subsidiar tomadas de decisões relacionadas a conservação e a gestão de recursos naturais. O presente estudo realizou uma análise temporal do uso e da cobertura do solo no estado de Sergipe, avaliando os distintos fatores impulsionadores deste processo no período entre 1985-2020. As informações relativas às classes de cobertura e uso do solo e “cicatriz do fogo”, obtidas do Projeto MapBiomas, foram consolidadas em um banco de dados integrando-as às informações agropecuárias extraídas do Sistema IBGE de Recuperação Automática. A análise de regressão múltipla linear, realizada para avaliar as interrelações entre as distintas classes de uso do MapBiomas, indicaram a classe “agropecuária” como principal força motriz do processo de conversão de áreas naturais para áreas antropizadas (r2 = 0,99; p < 0,05), com perda de cerca de 40% das tipologias que compõem a classe “floresta” no estado. As análises de correlação destacaram significativa relação entre a diminuição da classe “floresta” e o acréscimo de áreas destinadas à plantação de milho (r = -0,62) na Caatinga, e laranja (r = -0,52) e coco-da-baía (r = -0,51) na Mata Atlântica. O intenso avanço das atividades agropecuárias em detrimento dos ambientes naturais florestais impõe sérias ameaças à diversidade biológica. Além da proteção dos ambientes naturais florestais, faz-se necessário avançar em iniciativas de recuperação de áreas degradadas e de regeneração florestal, com o objetivo de mitigar os impactos na biodiversidade e nos serviços ecossistêmicos no estado de Sergipe.
... Before Schellnhuber, however, several others referred to "tipping points" (although not using this name) to processes occurring in other systems. The French mathematician René Thom (1975) developed the "theory of catastrophes" to model embryogenesis, which was applied in different problems of ecological systems (Scheffer et al 2001), andCharney andQuirk (1975) proposed a dynamic of the Sahara, which is similar to the dynamic proposed by Oyama and Nobre (2003) on the transition of the Amazon from forest to savannah. ...
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This article investigates climate science as a cultural object. By pursuing the “logic of its aporias”, it is shown that climate science emerged at the confluence of the objective development of the means of production (constituting a “planetary general intellect”) and the countercultural movement of the 60s, which put ecology at its center, but was broader than mere “environmentalism”. This resulted in the emergence of new forms of sensibility and a qualitative transformation of the natural sciences, which recognized the autonomy and complexity of nature. The constitution of climate science is reconstructed by taking the IGBP’s Amsterdam Declaration as historical archive, and by discussing biographical aspects of representative scientists, in mediation with their work and their world-historical context. Yet, the limits of climate science are those of counterculture. Climate science and its institutions preserve aspects of the previous mechanistic science as well as remaining traces of commodity fetishism
... First are the concerns about the so-called "tipping point" involving the breakdown in rainfall recycling that sustains moisture conditions and, therefore, Amazonia's rainforest ecosystems. Climate models project that the tipping point will be reached in only 15-30 years, at which time a considerable portion of Amazonia's rainforest would transition into a new equilibrium state of either savanna or woody scrub vegetation (Oyama and Nobre 2003;Sampaio et al. 2007Sampaio et al. , 2018Lovejoy et al. 2018;Asher 2020). Amazonian deforestation also affects precipitation in other parts of South America, North America, and Europe (Gedney and Valdes 2000;Werth and Avissar 2002;Avissar and Werth 2005;Hasler et al. 2009;Arraut et al. 2012). ...
Article
Available Free Online at: https://theconversation.com/the-great-amazon-land-grab-how-brazils-government-is-clearing-the-way-for-deforestation-173416
... Wang, Alo, et al. (2011) and using the NCAR Community Climate System Model found that vegetation dynamics plays an important role in enhancing the decadal and multidecadal variability of South American precipitation, a feature that could not be captured unless dynamic vegetationclimate interactions was included in the model. In a future climate with greenhouse gas warming, the vegetationcarbon cycle-climate feedback could potentially shift the regional hydroclimate regime and profoundly change vegetation features in South America (Cox et al., 2004;Nobre et al., 2016;Oyama & Nobre, 2003). The earliest attempt to include vegetation-carbon-climate interactions in future projections revealed that the projected greenhouse gas warming could trigger a "tipping" of the system toward a new equilibrium state and abrupt dieback of the tropical forests, further exacerbating the warming (Cox et al., 2000(Cox et al., , 2004. ...
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South America, especially the Amazon region, is considered a hotspot of biosphere–atmosphere interactions and presents a unique challenge for regional climate modeling. Here, we evaluate the performance of a regional model in simulating the climate–vegetation system in South America and use the model to investigate the potential role of large‐scale warming in the recently observed trend of hydroclimate and vegetation. Compared with prescribing vegetation based on observational data, adding the predictive vegetation capacity to the regional climate model enabled the model to simulate the vegetation response to climate while sustaining the model performance in reproducing the mean, variability and extremes of the regional climate. The coupled vegetation–climate model captures the recent trends in hydroclimate and vegetation productivity and their spatial contrasts, including a trend toward warmer, drier, and less productive conditions in the Amazon and Nordeste regions and a trend toward cooler, wetter, and more productive condition in the La Plata region. Results from sensitivity experiment driven by detrended boundary forcing for the regional climate suggest that much of the trends in the Amazon and Nordeste regions can be attributed to the effects of large‐scale warming, but contribution from decadal variability also plays a role especially for the most recent decade. However, the trend in the La Plata region cannot be attenuated by the removal of the boundary forcing trend, indicating the role of large‐scale circulation pattern changes. The recent trends in vegetation productivity may be early manifestation of future changes in the Amazon and surrounding regions.
... Fernandes et al. 2015). In terms of climate-vegetation equilibrium timescales, Oyama and Nobre (2003) performed climate simulations using an atmospheric general circulation model to examine the potential equilibrium states after a complete Earth deforestation scenario, and found that a simulation run of 15 years (with vegetation updated every 3 years) was sufficient for the climate-vegetation system to reach equilibrium (notice that oceanic and atmospheric parameters were updated at monthly scale in their model). This climatevegetation equilibrium timescale (10 years) seems reasonable, as the climatic response time of the vegetation is expected to be small compared to the time scale of climatic variation to which it is responding (Webb 1986). ...
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We present an innovative mathematical model for studying the dynamics of forest ecosystems. Our model is determined by an age-structured reaction–diffusion–advection system in which the roles of the water resource and of the atmospheric activity are considered. The model is abstract but constructed in such a manner that it can be applied to real-world forest areas; thus it allows to establish an infinite number of scenarios for testing the robustness and resilience of forest ecosystems to anthropic actions or to climate change. We establish the well-posedness of the reaction–diffusion–advection model by using the method of characteristics and by reducing the initial system to a reaction–diffusion problem. The existence and stability of stationary homogeneous and stationary heterogeneous solutions are investigated, so as to prove that the model is able to reproduce relevant equilibrium states of the forest ecosystem. We show that the model fits with the principle of almost uniform precipitation over forested areas and of exponential decrease of precipitation over deforested areas. Furthermore, we present a selection of numerical simulations for an abstract forest ecosystem, in order to analyze the stability of the steady states, to investigate the impact of anthropic perturbations such as deforestation and to explore the effects of climate change on the dynamics of the forest ecosystem.
... 110 Although the Amazon tipping point has largely been ignored by policymakers and social scientists, 111 it has been a topic of discussion among natural scientists since the early 2000s. 112 As deforestation in the Amazon continues, scientists say, it is likely to trigger a dieback of large portions of the forest, replacing the biodiverse ecosystems that now exist with a dry grassland savannah. 113 In the absence of other factors, the tipping point would likely be reached when around 40% of the Amazon basin has been deforested. ...
Article
The genocide–ecocide nexus has become the topic of a small but growing body of scholarly literature. This literature has largely relied on the original concept of genocide as developed by Raphael Lemkin, with a particular focus on how he conceived colonialism and cultural genocide. While these foci are both legitimate and helpful, Lemkin's later work offers a different approach in theorising the nexus. After detailing the post-war development of Lemkin's thought from eight ‘fields’ of genocide to three genocidal ‘methods’, I demonstrate how his later framework better accounts for the intersection between ecocide and genocide and I find precedent for it in Lemkin's unpublished work on the History of Genocide, in which he discusses the case of indigenous peoples in California. I then test my modified genocide–ecocide nexus against the case of deforestation in the Amazon. I argue that Lemkin's later thought better theorises the relationship between micro- and macro-level ecological destruction. It also reveals a missing link in the genocide–ecocide nexus: ecocide is the type of violence that, by its nature, increases the likelihood of future genocides. I conclude that post-ecocide resource scarcity as a driver of genocide often plays an integral role in the genocide–ecocide nexus.
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A intensificação das atividades humanas sobre o meio ambiente exerce um impacto significativo sobre o clima terrestre. Esse fenômeno se reflete em um aumento das temperaturas globais e em alterações nos padrões anuais de precipitação. Os longos períodos sem chuva representam um sério desafio socioambiental, especialmente para o semiárido do Nordeste brasileiro, aumentando a vulnerabilidade hídrica da região. Compreender a vulnerabilidade hídrica é essencial para a gestão sustentável da água, considerando sua importância para a sociedade e os ecossistemas. Objetiva-se com este estudo analisar a variabilidade pluviométrica e o balanço hídrico no Território de Identidade do Sudoeste da Bahia (TISB),considerando sua importância para a sociedade e os ecossistemas. Os resultados indicam que o período chuvoso ocorre de outubro a abril, no entanto, as chuvas não são uniformemente distribuídas. A característica da temperatura do TISB é típica da região semiárida do Brasil, com variações sazonais. No TISB ocorrem altas taxas de evapotranspiração durante todo o ano. Os resultados deste estudo apontam para uma tendência geral de diminuição na média anual de precipitação ao longo do período analisado (32 anos). O déficit hídrico é comum a todos os municípios que fazem parte do TISB e ocorre durante todo o ano, impactando diretamente nas dimensões sociais e ambientais e na participação do TISB no PIB do Estado.
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Terrestrial, aquatic, and marine ecosystems regulate climate at local to global scales through exchanges of energy and matter with the atmosphere and assist with climate change mitigation through nature‐based climate solutions. Climate science is no longer a study of the physics of the atmosphere and oceans, but also the ecology of the biosphere. This is the promise of Earth system science: to transcend academic disciplines to enable study of the interacting physics, chemistry, and biology of the planet. However, long‐standing tension in protecting, restoring, and managing forest ecosystems to purposely improve climate evidences the difficulties of interdisciplinary science. For four centuries, forest management for climate betterment was argued, legislated, and ultimately dismissed, when nineteenth century atmospheric scientists narrowly defined climate science to the exclusion of ecology. Today's Earth system science, with its roots in global models of climate, unfolds in similar ways to the past. With Earth system models, geoscientists are again defining the ecology of the Earth system. Here we reframe Earth system science so that the biosphere and its ecology are equally integrated with the fluid Earth to enable Earth system prediction for planetary stewardship. Central to this is the need to overcome an intellectual heritage to the models that elevates geoscience and marginalizes ecology and local land knowledge. The call for kilometer‐scale atmospheric and ocean models, without concomitant scientific and computational investment in the land and biosphere, perpetuates the geophysical view of Earth and will not fully provide the comprehensive actionable information needed for a changing climate.
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Amazonia contains the most extensive tropical forests on Earth, but Amazon carbon sinks of atmospheric CO2 are declining, as deforestation and climate-change-associated droughts1–4 threaten to push these forests past a tipping point towards collapse5–8. Forests exhibit complex drought responses, indicating both resilience (photosynthetic greening) and vulnerability (browning and tree mortality), that are difficult to explain by climate variation alone9–17. Here we combine remotely sensed photosynthetic indices with ground-measured tree demography to identify mechanisms underlying drought resilience/vulnerability in different intact forest ecotopes18,19 (defined by water-table depth, soil fertility and texture, and vegetation characteristics). In higher-fertility southern Amazonia, drought response was structured by water-table depth, with resilient greening in shallow-water-table forests (where greater water availability heightened response to excess sunlight), contrasting with vulnerability (browning and excess tree mortality) over deeper water tables. Notably, the resilience of shallow-water-table forest weakened as drought lengthened. By contrast, lower-fertility northern Amazonia, with slower-growing but hardier trees (or, alternatively, tall forests, with deep-rooted water access), supported more-drought-resilient forests independent of water-table depth. This functional biogeography of drought response provides a framework for conservation decisions and improved predictions of heterogeneous forest responses to future climate changes, warning that Amazonia’s most productive forests are also at greatest risk, and that longer/more frequent droughts are undermining multiple ecohydrological strategies and capacities for Amazon forest resilience.
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Explaining tropical tree cover distribution in areas of intermediate rainfall is challenging, with fire’s role in limiting tree cover particularly controversial. We use a novel Bayesian approach to provide observational constraints on the strength of the influence of humans, fire, rainfall seasonality, heat stress, and wind throw on tropical tree cover. Rainfall has the largest relative impact on tree cover (11.6-39.6%), followed by direct human pressures (29.8-36.8%), heat stress (10.5-23.3%) and rainfall seasonality (6.3-22.8%). Fire has a smaller impact (0.2-3.2%) than other stresses, increasing to 0.3-5.2% when excluding human influence. However, we found a potential vulnerability of eastern Amazon and Indonesian forests to fire, with up to 2% forest loss for a 1% increase in burnt area. Our results suggest that vegetation models should focus on fire development for emerging fire regimes in tropical forests and revisit the linkages between rainfall, non-fire disturbances, land use and broad-scale vegetation distributions.
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For centuries, people have understood that forests, and our utilisation of them, influence the climate. With modern environmental concerns, there is now scientific, governmental, and popular interest in planting trees for climate protection. This book examines the historical origins of the idea that forests influence climate, the bitter controversy that ended the science, and its modern rebirth. Spanning the 1500s to the present, it provides a broad perspective across the physical and biological sciences, as well as the humanities, to explain the many ways forests influence climate. It describes their use in climate-smart forestry and as a natural climate solution, and demonstrates that in the forest–climate question, human and sylvan fates are linked. Accessibly written with minimal mathematics, it is ideal for students in environmental and related sciences, as well as anyone with an interest in understanding the environmental workings of forests and their interactions with climate.
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The grassland-forest ecotone is a highly diverse and complex region that encompasses a multitude of grasslands, savannas, and forests. Ecological and anthropogenic pressures are causing dramatic changes in the health of the landscapes within this ecotone. A new methodology was created using State and Transition Models and Remote Sensing to understand and assess the landscape health. This methodology used six spectral indices (MTVI, NDSVI, NDVI, NDWI, SATVI, and SWIR32) created from times series Landsat 4-5TM. These spectral indices and LiDAR were used to characterize the spatial, spectral, and temporal properties of vegetation states and substates across 20 sites within the grassland-forest ecotone region of North Dakota and Minnesota. This suite of characteristics was used to create spectral keys. These spectral keys were then used to identify states and substates of Landsat-scaled State and Transition Models within Sheyenne National Grasslands. The effectiveness of 6 State and Transition Models was tested using the metrics of kappa, producer’s accuracy, user’s accuracy, and overall accuracy. This methodology was successful in identifying Tallgrass, Mixed, and Sand Prairies states. The entirety of the Tallgrass Prairie State and Transition Model met with the highest overall accuracy of over 80%. Spectral mixing was one of the main causes for low overall accuracy within the State and Transition Models. The characteristics of these landscape State and Transition Models were then applied to create a baseline for determining landscape health. The properties of the vegetation states, substates, and transitions were then applied to calculate values for landscape health, and its’ four indicators (Vigor, Organization, Resilience, and Ecosystem Services). An example was then used to illustrate how these values for indicators of landscape health could be used to help identify problems or improve the landscape health. The metrics used to determine landscape health, and landscape State and Transition Models with remote sensing are an important step to monitoring, understanding, and researching the Landscape Health of the highly diverse grassland-forest ecotones of this world. The supplementary materials contain additional over time and phenology graphs ofecological sites and their managed lands for each study site.
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The mid-Holocene 'green' Sahara represents the largest anomaly of the atmosphere-biosphere system during the last 12 000 years. Although this anomaly is attributed to precessional forcing leading to a strong enhancement of the African monsoon, no climate model so far has been able to simulate the full extent of vegetation in the Sahara region 6000 years ago. Here two atmospheric general circulation models (LMD 5.3 and ECHAM 3) are asynchronously coupled to an equilibrium biogeography model to give steady-state simulations of climate and vegetation 6000 years ago, including biogeophysical feedback. The two model results are surprisingly different, and neither is fully realistic. ECHAM shows a large northward extension of vegetation in the western Dart of the Sahara only. LMD shows a much smaller and more zonal vegetation shift. These results are unaffected by the choice of 'green' or modern initial conditions. The inability of LMD to sustain a 'green' Sahara 6000 years ago is linked to the simulated strength of the tropical summer circulation. During the northern summer monsoon season, the meridional gradient of sea-level pressure and subsidence over the western Dart of northern Africa al-e both much weaker in ECHAM than in LMD in the present as well as the mid-Holocene. These features allow the surface moist air flux to penetrate further into northern Africa in ECHAM than in LMD. This comparison illustrates the importance of correct simulation of atmospheric circulation features for the sensitivity of climate models to changes in radiative forcing, particularly for regional climates where atmospheric changes are amplified by biosphere-atmosphere feedbacks.
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The Center for Weather Forecasting and Climate Studies-Center for ocean-Land-Atmosphere Studies (CPTEC-COLA)atmospheric general circulation model (AGCM)is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the model's performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern portions and underestimates it in the northern portions of these systems. The high-and low-level main circulation features such as the subtropical highs, subtropical jet streams, and storm tracks are depicted well by the model, albeit with different intensities from the reanalysis. The stationary waves of the Northern and Southern Hemispheres are weaker in the model; however, the dominant wavenumbers are similar to the observations. The energy budget analysis shows values of some radiative fluxes that are close to observations, but the unbalanced fluxes in the atmosphere and at the surface indicate that the radiation and cloud scheme parameterizations need to be improved. Besides these improvements, changes in the convection scheme and higher horizontal resolution to represent orographic effects better are being planned to improve the model's performance. Pages: 2965-2988
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Large-scale conversion of tropical forests into pastures or annual crops could lead to changes in the climate. We have used a coupled numerical model of the global atmosphere and biosphere (Center for Ocean-Land-Atmosphere GCM) to assess the effects of Amazonian deforestation on the regional and global climate. We found that when the Amazonian tropical forests were replaced by degraded grass (pasture) in the model, there was a significant increase in the mean surface temperature (about 2.5-degrees-C) and a decrease in the annual evapotranspiration (30% reduction), precipitation (25% reduction), and runoff (20% reduction) in the region. The differences between the two simulations were greatest during the dry season. The deforested case was associated with larger diurnal fluctuations of surface temperature and vapor pressure deficit; such effects have been observed in existing deforested areas in Amazonia. The calculated reduction in precipitation was larger than the calculated decrease in evapotranspiration, indicating a reduction in the regional moisture convergence. There was also an increase in the length of the dry season in the southern half of the Amazon Basin, which could have serious implications for the reestablishment of the tropical forests following massive deforestation since rainforests only occur where the dry season is very short or nonexistent. An empirical bioclimatic scheme based on an integrated soil moisture stress index was used to derive the movement of the savanna-forest boundary in response to the simulated climate change produced by large-scale deforestation. The implications of possible climate changes in adjacent regions are discussed. Pages: 957-988
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The environmental conditions associated with squall lines (SL) that were observed during the period of 13 April-13 May 1987 (GTE/ABLE-2B) originating at the northern coast of South America and propagating over the Amazon Basin are documented. The St, observed on 5-7 May are examined in more detail. The SL days had in common a stronger and deeper low-level jet when compared with the days without SL. Two possible explanations are found for the intensification of the low-level jet: propagating easterly waves in the tropical Atlantic, which eventually reach Manaus, and localized heat sources in the western Amazon. Both were observed on 5-6 May. It is suggested that numerical simulations should be performed to unravel the relative importance of each large-scale mechanism. Pages: 3163-3174
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A comprehensive analysis of the simple biosphere model (SIB) of Sellers et al. (1986) is performed in an effort to bridge the gap between the typical hydrological treatment of the land surface biosphere and the conventional general circulation model treatment, which is specified through a single parameter. Approximations are developed that stimulate the effects of reduced soil moisture more simply, maintaining the essence of the biophysical concepts utilized in SIB. Comparing the reduced parameter biosphere with those from the original formulation in a GCM and a zero-dimensional model shows the simplified version to reproduce the original results quite closely.
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All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.
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This paper reports on a set of paleoclimate simulations for 21, 16, 14, 11 and 6 ka (thousands of years ago) carried out with the Community Climate Model, Version 1 (CCM1) of the National Center for Atmospheric Research (NCAR). This climate model uses four interactive components that were not available in our previous simulations with the NCAR CCM0 (COHMAP, 1988Science, 241, 1043–1052; Wright et al., 1993Global Climate Since the Last Glocial Maximum, University of Minnesota Press, MN): soil moisture, snow hydrology, sea-ice, and mixed-layer ocean temperature. The new simulations also use new estimates of ice sheet height and size from (Peltier 1994, Science, 265, 195–201), and synchronize the astronomically dated orbital forcing with the ice sheet and atmospheric CO2 levels corrected from radiocarbon years to calendar years. The CCM1 simulations agree with the previous simulations in their most general characteristics. The 21 ka climate is cold and dry, in response to the presence of the ice sheets and lowered CO2 levels. The period 14–6 ka has strengthened northern summer monsoons and warm mid-latitude continental interiors in response to orbital changes. Regional differences between the CCM1 and CCM0 simulations can be traced to the effects of either the new interactive model components or the new boundary conditions. CCM1 simulates climate processes more realistically, but has additional degrees of freedom that can allow the model to ‘drift’ toward less realistic solutions in some instances. The CCM1 simulations are expressed in terms of equilibrium vegetation using BIOME 1, and indicate large shifts in biomes. Northern tundra and forest biomes are displaced southward at glacial maximum and subtropical deserts contract in the mid-Holocene when monsoons strengthen. These vegetation changes could, if simulated interactively, introduce additional climate feedbacks. The total area of vegetated land remains nearly constant through time because the exposure of continental shelves with lowered sea level largely compensates for the land covered by the expanded ice sheets.
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A conceptual model has been developed for the analysis of atmosphere-vegetation interaction in subtropical deserts. The model can exhibit multiple stable states in the system: a ``desert'' equilibrium with low precipitation and absent vegetation and a ``green'' equilibrium with moderate precipitation and permanent vegetation cover. The conceptual model is applied to interpret the results of two climate-vegetation models: a comprehensive coupled atmosphere-biome model and a simple box model. In both applications, two stable states exist for the western Sahara/Sahel region for the present-day climate, and the only green equilibrium is found for the mid-Holocene climate. The latter agrees well with paleoreconstructions of Sahara/Sahel climate and vegetation. It is shown that for present-day climate the green equilibrium is less probable than the desert equilibrium, and this explains the existence of the Sahara desert as it is today. The difference in albedo between the desert and vegetation cover appears to be the main parameter that controls an existence of multiple stable states. The Charney's mechanism of self-stabilization of subtropical deserts is generalized by accounting for atmospheric hydrology, the heat and moisture exchange at the side boundaries, and taking into account the dynamic properties of the surface. The generalized mechanism explains the self-stabilization of both desert and vegetation in the western Sahara/Sahel region. The role of surface roughness in climate-vegetation interaction is shown to be of secondary importance in comparison with albedo. Furthermore, for the high albedo, precipitation increases with increasing roughness while, for the low albedo, the opposite is found.
Article
A numerical simulation study of the influence of surface albedo on July circulation in semi‐arid regions, using the general circulation model (GCM) of the Goddard Laboratory of Atmospheric Sciences (GLAS) is presented. The results are based on two 47‐day integrations. In the first integration, called the control run, the surface albedo was normally prescribed, whereas in the second integration, called the anomaly run, the surface albedo was modified in four regions: the Sahel in Africa, the western Great Plains in the United States, the Thar Desert border in the Indian subcontinent, and northeast Brazil in South America. This experiment is similar to that of Charney et al. (1977); however, it was performed with the GLAS model with vastly different boundary forcings and several changes in the physical parameterizations. Each run was started from observed initial conditions for 15 June 1979, based on NMC analysis. An analysis of the two simulations shows that in the Sahel, and the Thar Desert border regions the current results again show reduced precipitation with increased surface albedo in accordance with Charney et al. (1977) and Charney (1975). The semi‐arid northeast Brazil region, which had a winter circulation, also conforms with Charney's (1975) hypothesis. However, the Great Plains region was an exception. There the total precipitation in two simulations was unchanged, as was the total cloudiness. In this region, the convective precipitation was reduced somewhat, while the large‐scale precipitation compensated this decrease by approximately the same amount. The lack of albedo impact on precipitation in the Great Plains region could be due to the influence of the Rocky Mountains in generating variations in the large‐scale flow. The purpose of repeating Charney's albedo experiment was to test the sensitivity of his earlier results with the current GLAS GCM which has substantially modified physical parameterizations, particularly the planetary boundary layer (PBL), crucially important for such impact studies. Taking into account that both the GCM and the initial conditions of the atmosphere were different, it is worth noting that this experiment still provides support for Charney's hypothesis (1975) regarding the influence of surface albedo on mean‐monthly climatology in the subtropical desert margin regions. Another important influence noted was the variability of mean monthly simulation in areas far away from the albedo anomaly regions. Because the differences occur in regions of high observed climatological variability, it is necessary to separate the contribution of albedo anomalies as opposed to the model variability. The influence of surface albedo changes to produce large changes in the mean montly circulation elsewhere is very intriguing and needs further investigation.
Article
A simple dynamic model relating forest area in a region, its contribution to dry season precipitation and the effect on its own establishment was developed. The model equation shows hysteresis between forest and savannas as a function of imported dry season precipitation. Regions are either dominated by forests or savannas, with each ecosystem showing stability despite changes in imported dry season precipitation. Deforestation beyond a certain threshold value, however, could cause a collapse of forest ecosystems and replacement by savannas in marginal areas. The predictions of this model corroborate pollen core analysis in the Amazon basin, where historical stability of tropical forest cover has been shown despite global climate change.
Article
An asynchronously coupled global atmosphere–biome model is used to assess the stability of the atmosphere–vegetation system under present-day conditions of solar irradiation and sea-surface temperatures. When initialized with different land-surface conditions (1, the continents, except for regions of inland ice, completely covered with forest; 2, with grassland; 3, with (dark) desert; and 4, with (bright) sand desert), the atmosphere–biome model finds two equilibrium solutions: the first solution yields the present-day distribution of subtropical deserts, the second reveals a moister climate in North Africa and Central East Asia and thereby a northward shift of vegetation particularly in the south-western Sahara. The first solution is obtained with initial condition 4, and the second with 1, 2, 3. When comparing these results with an earlier study of biogeophysical feedback in the African and Asian monsoon area, it can be concluded that North Africa is probably the region on Earth which is most sensitive considering bifurcations of the atmosphere–vegetation system at the global scale.
Article
 An asynchronously coupled global atmosphere-biome model is used to assess the dynamics of deserts and drought in the Sahel, Saudi-Arabia and the Indian subcontinent. Under present-day conditions of solar irradiation and sea-surface temperatures, the model finds two solutions: the first solution yields the present-day distribution of vegetation and deserts and the second shows a northward spread of savanna and xerophytic shrub of some 600 km, particularly in the southwest Sahara. Comparison of atmospheric states associated with these solutions corroborates Charney’s theory of a self-induction of deserts through albedo enhancement in the Sahel. Over the Indian subcontinent, changes in vegetation are mainly caused by a positive feedback between increased soil moisture and stronger summer monsoon.
Article
The Kappa statistic is presented as an objective tool for comparing global vegetation maps. Such maps can result from either compilations of observed spatial patterns or from simulations from models that are global in scope. The method is illustrated by comparing global maps resulting from applying a modified Holdridge Life Zone Classification to current climate and several climate change scenarios (CO2 doubling). These scenarios were based on the results of several different general circulation models (GCMs). The direction of change in simulated vegetation patterns between different GCMs was found to be quite similar for all future projections. Although there were differences in magnitude and extent, all simulations indicate potential for enormous ecological change. The Kappa statistic proved to be a useful and straightforward measure of agreement between the different global vegetation maps. Furthermore, Kappa statistics for individual vegetation zones clearly indicated differences and similarities between those maps. The Kappa statistic was found to be most useful for rank ordering of agreement, both across a series of maps and across the various vegetation zones within a map.
Article
Using a coupled atmosphere-land-vegetation model of intermediate complexity, the authors explore how vegetation-climate interaction and internal climate variability might influence the vegetation distribution in Africa. When the model is forced by observed climatological sea surface temperature (SST), positive feedbacks from vegetation changes tend to increase the spatial gradient between desert regions and forest regions at the expense of savanna regions. When interannual variation of SST is included, the climate variability tends to reduce rainfall and vegetation in the wetter regions and to increase them in the drier regions along this gradient, resulting in a smoother desert-forest transition. This effect is most dramatically demonstrated in a model parameter regime for which multiple equilibria (either a desertlike or a forestlike Sahel) can exist when strong vegetation-climate feedbacks are allowed. However, the presence of a variable SST drives the desertlike state and the forestlike state toward an intermediate grasslike state, because of nonlinearities in the coupled system. Both vegetation and interannual variability thus play active roles in shaping the subtropical savanna ecosystem.
Article
Components of the Simple Biosphere Model (SiB) of Sellers et al. (1986) were used to generate global monthly fields of surface albedo (0.4-4.0 microns), roughness length and minimum surface (stomatal) resistance. SiB consists of three submodels which describe the roles of radiative transfer, turbulent transfer and surface resistance in determining the energy balance of the vegetated land surface. These three submodels were detached from SiB and used on the SiB parameter set (total and green leaf area index, leaf angle orientation, canopy dimensions, etc.) to calculate global monthly fields of albedo, roughness length and minimum stomatal resistance at 1 x 1 deg resolution. Time series of various parameters are also displayed for each vegetation type for specified grid points. The SiB results compare reasonably well with appropriate measurements obtained from the literature and have the additional merit of being mutually consistent; the three submodels use many common parameters, which ensures that, for each grid area, the calculated surface properties are closely interrelated as is the case in nature. The derived fields provide a check on the operation of the submodels and the correctness of the parameter set. They can also be used as prescribed fields for GCMs that do not have biophysically based land surface parameterizations.
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Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered.
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Despite the very active deforestation of the last decade, the Amazon Basin is still primarily covered with trees and is a system in equilibrium. The Andes form a barrier at the western end of the basin and, coupled with the prevailing easterly winds, ensure an almost unique precipitation and water-recycling regime. On average 50 percent of the precipitation is recycled, and in some areas even more. The soils are poor. Most of the nitrogen and phosphorus is found in the soil, and the remaining nutrient elements are found in the standing biomass. There is some nutrient recycling and little loss from the intact ecosystem, and the small input of nutrients from precipitation maintains a small positive nutrient balance. Continued large-scale deforestation is likely to lead to increased erosion and water runoff with initial flooding in the lower Amazon, together with reduced evapotranspiration and ultimately reduced precipitation. Reduced precipitation in the Amazon could increase the tendency toward continentality and adversely affect climate and the present agriculture in south-central Brazil.
July circulation in semi-arid regions using the A simplified biosphere model for global climate studies The role of vegetation-climate interaction and interanuual variability in shaping the African savanna
  • Y C Sud
  • M Fennessy Glas Gcm
  • J Xue
  • P J Sellers
  • J L Kinter
  • J Shukla
  • N Zeng
  • J D Neelin
Sud, Y. C., and M. Fennessy, A study of the influence of surface albedo on July circulation in semi-arid regions using the GLAS GCM, J. Climatol., 2, 105 – 125, 1982. Xue, Y., P. J. Sellers, J. L. Kinter, and J. Shukla, A simplified biosphere model for global climate studies, J. Climate, 4, 345 – 364, 1991. Zeng, N., and J. D. Neelin, The role of vegetation-climate interaction and interanuual variability in shaping the African savanna, J. Climate, 13, 2665 – 2670, 2000. ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ À C. A. Nobre, Centro de Previsã de Tempo e Estudos Climá, Instituto Nacional de Pesquisas Espaciais, 12630-000, Cachoeira Paulista, SP, Brazil. M. D. Oyama, Centro Té Aeroespacial, Instituto de Aeroná e Espaç, Divisã de Ciê Atmosfé, Pç Marechal Eduardo Gomes, 50, 12228-904, Sã José dos Campos, SP, Brazil. (oyama@iae.cta.br) CLM 5 -4 OYAMA AND NOBRE: A NEW CLIMATE-VEGETATION STATE