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Climate change 2001: The scientific basis
... The attribution model described here presupposes a linear-additive model of the forcing, which is not necessarily the case (Ramaswamy et al. 2001). Our approach differs from more conventional approaches to attribution described in (Zwiers 1999) in that we do not explicitly compare model outputs to observations to make attributions to given forcings. ...
... For the diurnal cycle (D) this was typically because the expert did not feel sufficiently well acquainted with the data and/or did cate 50% or more of the probability mass to aerosol forcing < 1.5 W m~2, but fewer than half of the experts allocate more than 70% of the probability mass to this range. The low ranges of aerosol and solar forcing above encompass most of the uncertainty range for estimates of these forcings in (Shine and Forster 1999) and (Ramaswamy et al. 2001)-that is, the socalled low ranges here correspond to the more conventional views of the forcings. The considerable spread of probability mass across the low and high forcing ranges for most experts is consistent with the "low confidence" afforded aerosol and solar forcing estimates in (Shine and Forster 1999) and (Ramaswamy et al. 2001). ...
... The low ranges of aerosol and solar forcing above encompass most of the uncertainty range for estimates of these forcings in (Shine and Forster 1999) and (Ramaswamy et al. 2001)-that is, the socalled low ranges here correspond to the more conventional views of the forcings. The considerable spread of probability mass across the low and high forcing ranges for most experts is consistent with the "low confidence" afforded aerosol and solar forcing estimates in (Shine and Forster 1999) and (Ramaswamy et al. 2001). ...
... | Ramaswamy et al. 2001). Modification of cloud albedos through the seeding of smaller droplets (brightening and increase in cloud lifetimes) (Twomey 1977), or by the incorporation of absorbing aerosols (darkening) (Kaufman and Nakajima 1993), constitute "indirect" radiative forcing effects for which model uncertainties are large compared to the levels needed to assess their overall climate significance. ...
... However, current spaceborne techniques seem capable of inferring only rough proxies, such as the complex refractive index. In situ airborne sensors provide detailed information about particle microphysics and chemical composition that are unachievable through other means, but their coverage is limited. 1 See, for example, Penner et al. (1994); Heintzenberg et al. (1996); Working Group I of the Intergovernmental Panel on Climate Change (IPCC; Penner et al. 2001;Ramaswamy et al. 2001); committees of the National Academy of Sciences (Seinfeld et at. 1996;Molina et al. 2001);Charlson (2001); the Department of Energy (DOE) Tropospheric Aerosol Program planning group (DOE 2001); the National Aerosol-Climate Interactions Program (NACIP) Scientific Steering Committee (Ramanathan et al. 2002); the World Meteorological Organization Global Atmosphere Watch Scientific Advisory Group for Aerosol (Baltensperger et al. 2003); and the Climate Change Science Program Office (Mahoney et al. 2003). ...
... PARAGON is motivated by the need to understand the sensitivity of the climate system to changes in atmospheric constituents, to reduce uncertainties in climate models, and to interpret and integrate a diverse collection of data pertaining to atmospheric aerosols. As noted by many researchers, the uncertainty in anthropogenic aerosol forcing from each of the direct and indirect effects is of the same magnitude as the forcing itself and is the dominant source of uncertainty in estimates of anthropogenic climate forcing (e.g., Penner et al. 2001;Ramaswamy et al. 2001). Reducing model uncertainties is the only way to obtain reliable inputs to decisions regarding climate adaptation and mitigation. ...
Aerosols are generated and transformed by myriad processes operating across many spatial and temporal scales. Evaluation of climate models and their sensitivity to changes, such as in greenhouse gas abundances, requires quantifying natural and anthropogenic aerosol forcings and accounting for other critical factors, such as cloud feedbacks. High accuracy is required to provide sufficient sensitivity to perturbations, separate anthropogenic from natural influences, and develop confidence in inputs used to support policy decisions. Although many relevant data sources exist, the aerosol research community does not currently have the means to combine these diverse inputs into an integrated data set for maximum scientific benefit. Bridging observational gaps, adapting to evolving measurements, and establishing rigorous protocols for evaluating models are necessary, while simultaneously maintaining consistent, well understood accuracies. The Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) concept represents a systematic, integrated approach to global aerosol characterization, bringing together modern measurement and modeling techniques, geospatial statistics methodologies, and high-performance information technologies to provide the machinery necessary for achieving a comprehensive understanding of how aerosol physical, chemical, and radiative processes impact the Earth system. We outline a framework for integrating and interpreting observations and models and establishing an accurate, consistent and cohesive long-term data record. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc.
... This test is widely used for climatic and environmental time series trends evaluation (Chen et al. 2007, Proutsos et al. 2008, Tigkas 2008, Karpouzos et al. 2010, because as a non-parametric method requires only data independence and is tolerant to outliers. It is a reliable method to identify monotonic linear and non-linear trends in non-normal data sets (Helsel and Hirsch, 1992). The slope of each trend evaluated from the climatic data, is identified by the Sen method (here referred as Q Sen slope), as a median of all possible slopes (Sen 1968, Helsel andHirsch 1992). ...
... It is a reliable method to identify monotonic linear and non-linear trends in non-normal data sets (Helsel and Hirsch, 1992). The slope of each trend evaluated from the climatic data, is identified by the Sen method (here referred as Q Sen slope), as a median of all possible slopes (Sen 1968, Helsel andHirsch 1992). The variability of trends and slopes with altitude is also examined and a further investigation is conducted through the categorization of the stations as north (Arnea, Krania, Fournas, Metsovo and Aspropotamos) and south (Artemisia, Vamvakou, Tripolis and Kalavrita). ...
This study aims to investigate (minimum, mean and maximum) temperature trends at high altitudes in Greece. The temperature variations can affect plant phenological behaviour and growth. The dates of growth initiation or the length of the growing period are defined mostly by minimum temperature. On the other hand, maximum and mean temperatures have a direct effect on water availability, affecting growth and development rates of rain fed ecosystems, especially during the water-stressed summer period. Data from 9 meteorological stations at altitudes 520-1310 m, covering the time period 1960-2006, are analyzed for temperature variability. The stations are located in agricultural and forest environments with no significant land use changes over the study period. Trends of temperature are calculated on a monthly, seasonal as well as an annual basis under different levels of confidence. Generally, significant yearly decreases of mean temperature were observed. Averaged for all sites, the annual mean temperature decrease rate is – 0.015 oC y-1. In all months and seasons, the average trends of mean temperature are also negative, with November becoming coolest (– 0.061 oC y-1) and autumn showing the greatest temperature decrease (– 0.032 oC y-1). In comparison with mean temperature, an even greater decreasing rate is observed for minimum temperature (– 0.027 oC y-1). Monthly minimum temperature trends are similar to those of mean temperature. On a seasonal basis, however, it is in spring that minimum temperature shows maximum negative trend (– 0.038 oC y-1). On the contrary, maximum temperature slope has a positive annual trend, with a site-average of + 0.011 oC y-1. The greatest increasing rate (+ 0.037 oC y-1) is observed in summer with July becoming warmest. In some months, even maximum temperature becomes cooler with November, again, becoming coolest (– 0.045 oC y-1). Conclusively, high altitude sites in Greece generally become cooler, with reference even to maximum temperature in some cases.
... Idealized radiative forcing is the net flux at the TOA without any response anywhere after the forcing agents were imposed. In such a way, the doubled CO 2 concentration corresponds to approximately 4.37 W m −2 (Ramaswamy et al., 2001 ). As research progressed , climate scientists began to understand that the forcing responsible for the change in T s is the unbalanced radiation after rapid adjustments. ...
... For example , the stratosphere can adjust to radiative ilibrium within one month; whereas, the changes in the troposphere, which are of greater concern, are slower and caused by the forcing after stratospheric adjustment . Taking this into consideration, the Intergovernmental Panel on Climate Change (IPCC) modified the definition of radiative forcing in its third assessment report (TAR), with the doubled CO 2 forcing revised to 3.71 W m −2 (Ramaswamy et al., 2001). Although the above concept of forcing was preserved, other methods to calculate the forcing were proposed in the fourth IPCC report (Forster et al., 2007), including more rapid processes (but slower than the stratospheric adjustment ), such as aerosol-related cloud changes (Jacob et al., 2005) and temperature adjustment in the troposphere (Hansen et al., 2005). ...
Climate sensitivity is an important index that measures the relationship between the increase in greenhouse gases and the magnitude of global warming. Uncertainties in climate change projection and climate modeling are mostly related to the climate sensitivity. The climate sensitivities of coupled climate models determine the magnitudes of the projected global warming. In this paper, the authors thoroughly review the literature on climate sensitivity, and discuss issues related to climate feedback processes and the methods used in estimating the equilibrium climate sensitivity and transient climate response (TCR), including the TCR to cumulative CO2 emissions. After presenting a summary of the sources that affect the uncertainty of climate sensitivity, the impact of climate sensitivity on climate change projection is discussed by addressing the uncertainties in 2°C warming. Challenges that call for further investigation in the research community, in particular the Chinese community, are discussed.
... The third complication concerns external forcing. Although the radiative impact of increased greenhouse gas concentrations is known with a good accuracy, there are large uncertainties in other sources of climate forcing, particularly the direct radiative effects of anthropogenic aerosols and the impact of aerosols on clouds (Ramaswamy et al., 2001). Thus, differences between simulated and observed climate changes could result both from a misrepresentation of the external forcing in the model and from a misrepresentation of the feedback processes that regulate the climate response to a given forcing. ...
... This is a major problem particularly for studies based on the relatively small and short-term temperature changes following volcanic eruptions. In studies based on temperature evolution during the instrumental period, the largest problem is the uncertainty in external forcing, particularly the poorly known extent to which the positive greenhouse-gas-induced radiative forcing has been compensated by negative aerosol forcing (Boucher and Haywood, 2001; Ramaswamy et al., 2001 ). To alleviate this problem, several studies (e.g. ...
How much can we trust model-based projections of future anthropogenic climate change? This review attempts to give an overview of this important but difficult topic by using three main lines of evidence: the skill of models in simulating present-day climate, intermodel agreement on future climate changes, and the ability of models to simulate climate changes that have already occurred. A comparison of simulated and observed present-day climates shows good agreement for many basic variables, particularly at large horizontal scales, and a tendency for biases to vary in sign between different models, but there is a risk that these features might be partly a result of tuning. Overall, the connection between model skill in simulating present-day climate and the skill in simulating future climate changes is poorly known. An intercomparison of future climate changes between models shows a better agreement for changes in temperature than that for precipitation and sea level pressure, but some aspects of change in the latter two variables are also quite consistent between models. A comparison of simulations with observed climate changes is, in principle, a good test for the models, but there are several complications. Nonetheless, models have skilfully simulated many large-scale aspects of observed climate changes, including but not limited to the evolution of the global mean surface air temperature in the 20th century. Furthermore, although there is no detailed agreement between the simulated and observed geographical patterns of change, the grid box scale temperature, precipitation and pressure changes observed during the past half-century generally fall within the range of model results. Considering the difficulties associated with other sources of information, the variation of climate changes between different models is probably the most meaningful measure of uncertainty that is presently available. In general, however, this measure is more likely to underestimate than overestimate the actual uncertainty.
... The balance between altered surface radiative and heat fluxes caused by aerosols determines the actual impact of aerosols on surface temperature changes. Previous modeling studies suggests that at the current time, the cooling caused by sulfate aerosols represents a significant offset in value to the warming effect caused by so-called greenhouse gases such as CO 2 , CH 4 , N 2 O, and O 3 (Roeckner et al., 1999; Ramaswamy et al., 2001). In the case of BC aerosols, however, the uneven heating/cooling effect across the atmosphere-Earth's surface interface further complicate the surface energy budget and thus the otherwise near constant relationship between the radiative forcing of a given species and the resultant change in surface temperature established for other radiatively important species (e.g., Manabe and Wetherald, 1967). ...
... As the results have demonstrated, responses of the modeled climate system to the BC aerosol radiative forcings are complicated and in many occasions and locations the resultant changes in the atmosphere or at the Earth's surface compensate each other. With an absolute amount 3 times higher than that of the TOA forcing, the surface forcing of BC is an extremely important factor in analyzing the climate impact of BC. Results from this study and many previous ones (see Haywood and Boucher 2000; Penner et al., 2001; Ramaswamy et al., 2001; Ramanathan et al., 2001) challenge the practice of using only the TOA radiative forcing by BC to project the possible climate impact of BC. In addition, the result of this study does not suggest that BC aerosols contribute to a significant increase in land-surface temperature with annual emissions of ~14 TgC (note that similar numbers have been used in several related studies). ...
A three-dimensional interactive aerosol-climate model has been developed
and used to study the climatic impact of black carbon (BC) aerosols.
When compared with the model's natural variability, significant
global-scale changes caused by BC aerosols occurred in surface latent
and sensible heat flux, surface net long-wave radiative flux, planetary
boundary layer height, convective precipitation (all negative), and
low-cloud coverage (positive), all closely related to the hydrological
cycle. The most significant regional change caused by BC revealed in
this study is in precipitation that occurs in the tropics (shift of
precipitation center in the ITCZ) and in the middle and high latitudes
of the Northern Hemisphere (change in snow depth). Influenced by BC
caused changes in cloud cover and surface albedo, the interactive model
provides smaller positive all-sky forcing at the top of atmosphere (TOA)
and larger negative forcing at the surface than the offline diagnostics
(the direct forcings). The actual solar radiative forcings by BC derived
from the interactive model also exhibit significant interannual
variations that are up to 4 times as large as their means. Based on the
revealed changes in cloud radiative forcing by BC, a non-Twomey-Albrecht
indirect forcing by BC that alters radiative budgets by changing cloud
cover via thermodynamics rather than microphysics is also defined. It
has been demonstrated that with an absolute amount more than 2 times
higher than that of the TOA forcing, the surface forcing by BC is a very
important factor in analyzing the climatic impact of BC. The result of
this study suggests that with a constant annual emission of 14 TgC, BC
aerosols do not cause a significant change in global-mean surface
temperature. The calculated surface temperature change is determined by
a subtle balance among changes in surface energy budget as well as in
the hydrological cycle, all caused by BC forcing and often compensate
each other. The result of this study shows that the influences of BC
aerosols on climate and environment are more significant in regional
scale than in global scale. Important feedbacks between BC radiative
effects and climate dynamics revealed in this study suggest the
importance of using interactive aerosol-climate models to address the
issues related to the climate impacts of aerosols.
... See, e.g., https://www.realclimate.org/index.php/archives/2010/01/plass-and-the-surface-budget-fallacy/#more-2652 as observed in the satellite and instrumental record (Ramaswamy et al. 2001;Shine et al. 2003). ...
Syukoro (Suki) Manabe’s Nobel Prize in physics was awarded largely for his early work on one-dimensional models of “radiative-convective equilibrium” (RCE), which produced the first credible estimates of Earth’s climate sensitivity. This article reviews that work and tries to identify those aspects that make it so distinctive.
We argue that Manabe’s model of RCE contained three crucial ingredients. These are i) a tight convective coupling of the surface to the troposphere ii) an assumption of fixed relative humidity rather than fixed absolute humidity, and iii) a sufficiently realistic representation of greenhouse gas radiative transfer. Previous studies had separately identified these key ingredients, but none had properly combined them. We then discuss each of these ingredients in turn, highlighting how subsequent research in the intervening decades has only cemented their importance for understanding global climate change. We close by reflecting on the elegance of Manabe’s approach and its lasting value.
... The analysis by Hansen et al. (2005), as well as other recent studies (see, e.g., the reviews by Ramaswamy et al. 2001;Kopp et al. 2005b;Lean et al. 2005;Loeb and Manalo-Smith 2005;Lohmann and Feichter 2005;Pilewskie et al. 2005;Bates et al. 2006;Penner et al. 2006), indicates that the current uncertainties in the TSI and aerosol forcings are so large that they preclude meaningful climate model evaluation by comparison with observed global temperature change. These uncertainties must be reduced significantly for uncertainty in climate sensitivity to be adequately constrained (Schwartz 2004). ...
... Cryosphere response: Changes in the cryosphere in high latitudes through changes in albedo, sea ice, and meltwater can change the surface temperature, lapse rate, and meridional temperature gradient, which can induce local and larger scale changes in warming rate ( Hansen and Takahashi, 1984;Held, 1993). Heterogeneous radiative forcing: Atmospheric radiative forcing differs from one region to another due to differences in aerosol loading and distributions of some trace gases ( Ramanathan et al., 1987;Ramaswamy et al., 2001). Given the clear reasons for differences in regional warming rates, one should not expect all regions to warm together. ...
The Earth has warmed over the past century. The warming rate (amount of warming over a given period) varies in time and space. Observations show a recent increase in global mean warming rate, which is initially maintained in model projections, but which diverges substantially in future depending on the emissions scenario followed. Scenarios that stabilize forcing lead to much lower warming rates, as the rate depends on the change in forcing, not the amount. Warming rates vary spatially across the planet, but most areas show a shift toward higher warming rates in recent decades. The areal distribution of warming rates is also changing shape to include a longer tail in recent decades. Some areas of the planet are already experiencing extreme warming rates of about 1 °C/decade. The fat tail in areal distribution of warming rates is pronounced in model runs when the forcing and global mean warming rate is increasing, and indicates a climate state more prone to regime transitions. The area-proportion of the Earth displaying warming/cooling trends is shown to be directly related to the global mean warming rate, especially for trends of length 15 years and longer. Since the global mean warming rate depends on the forcing rate, the proportion of warming/cooling trend areas in future also depends critically on the choice of future forcing scenario.
... This was raised to 21 in the 1995 Second Assessment Report used by the Kyoto Protocol (Schimel et al., 1996). In 2001 it was raised to 23 in the Third Assessment Report (Ramaswamy et al., 2001) and then to 25 in the 2007 Fourth Assessment Report (Forster et al., 2007). The Fifth Assessment Report (AR5) increased this to 28 if calculated in the same way (100-year time horizon and no climate-carbon feedbacks in response to CH4 emissions), but also reports a value of 34 when these feedbacks are included (Myhre et al., 2013, p. 714). ...
Tropical hydroelectric dams emit substantial amounts of greenhouse gases. A major source of emission is the carbon released from above-water decay of the trees that are killed by flooding. The water in the reservoir emits carbon dioxide (CO2), either through bubbling or diffusion through the reservoir surface or from the water being released through the turbines and spillways. Nitrous oxide (N2O) is a greenhouse gas with a contribution from reservoirs. Methane (CH4) emission is also a major contribution of hydroelectric dams to global warming. The value of time is crucial in comparing the global warming impact of hydropower and fossil fuels or other energy sources. Carbon credit that is currently granted to hydropower projects through the Clean Development Mechanism (CDM) is one of the most controversial aspects of efforts to mitigate global warming under the United Nations Framework Convention on Climate Change (UNFCCC).
... The increase in the static stability, shown in, Fig. 17, is because convection follows a less steep lapse rate in the warmer and moister climate and the increase is to first approximation proportional to the increase in specific humidity. Following the presentation by Sugi et al. (2002) the approximate energy equation in the tropics can be formulated as: (Holton 1992;Knutson and Manabe, 1995 be written as: ...
... In particular CO 2 , CH 4 and N 2 O concentrations (Hansen et al., 2007): data are available at http://data.giss.nasa.gov (since 1850); we calculate radiative forcings (GHGRF) as in Ramaswamy et al. (2001). ...
At present the role of natural variability in influencing climate behaviour is widely discussed. The generally accepted view is that atmosphere-ocean coupled circulation patterns are able to amplify or reduce temperature increase from interannual to multidecadal time ranges, leaving the principal driving role to anthropogenic forcings. In this framework, the influence of these circulation patterns is considered synchronous with global temperature changes. Here we would like to investigate if there exists a lagged influence of these indices on temperature. In doing so, an extension of the Granger causality technique, which permits to test both direct and indirect causal influences, is applied. A lagged influence of natural variability is not evident in our analysis, if we except weak influences of some peculiar circulation indices in specific periods.
... There is a sense though, that the inclusion of CH 4 was an afterthought, perhaps added in because it can be measured simultaneously with CO 2 on many gas chromatographs. Indeed, the significance of CH 4 as an agent of anthropogenic climate change was just beginning to come in to focus at the time (Hansen et al. 2000, Ramaswamy 2001), so its limited attention in streams and rivers is not necessarily surprising. Following these relatively quiet forays, two publications triggered a sudden increase in research activity during the past five years. ...
Streams and rivers can substantially modify organic carbon (OC) inputs from terrestrial landscapes, and much of this processing is the result of microbial respiration. While carbon dioxide (CO2) is the major end-product of ecosystem respiration, methane (CH4) is also present in many fluvial environments even though methanogenesis typically requires anoxic conditions that may be scarce in these systems. Given recent recognition of the pervasiveness of this greenhouse gas in streams and rivers, we synthesized existing research and data to identify patterns and drivers of CH4, knowledge gaps, and research opportunities. This included examining the history of lotic CH4 research, creating a database of concentrations and fluxes (MethDB) to generate a global-scale estimate of fluvial CH4 efflux, and developing a conceptual framework and using this framework to consider how human activities may modify fluvial CH4 dynamics. Current understanding of CH4 in streams and rivers has been strongly influenced by goals of understanding OC processing and quantifying the contribution of CH4 to ecosystem C fluxes. Less effort has been directed towards investigating processes that dictate in situ CH4 production and loss. CH4 makes a meager contribution to watershed or landscape C budgets, but streams and rivers are often significant CH4 sources to the atmosphere across these same spatial extents. Most fluvial systems are supersaturated with CH4 and we estimate an annual global emission of 26.8 Tg CH4, equivalent to ∼15-40% of wetland and lake effluxes, respectively. Less clear is the role of CH4 oxidation, methanogenesis, and total anaerobic respiration to whole ecosystem production and respiration. Controls on CH4 generation and persistence can be viewed in terms of proximate controls that influence methanogenesis (organic matter, temperature, alternative electron acceptors, nutrients) and distal geomorphic and hydrologic drivers. Multiple controls combined with its extreme redox status and low solubility result in high spatial and temporal variance of CH4 in fluvial environments, which presents a substantial challenge for understanding its larger-scale dynamics. Further understanding of CH4 production and consumption, anaerobic metabolism, and ecosystem energetics in streams and rivers can be achieved through more directed studies and comparison with knowledge from terrestrial, wetland, and aquatic disciplines.
... This was raised to 21 in the 1995 Second Assessment Report used by the Kyoto Protocol (Schimel et al., 1996). In 2001 it was raised to 23 in the Third Assessment Report (Ramaswamy et al., 2001) and then to 25 in the 2007 Fourth Assessment Report (Forster et al., 2007). The Fifth Assessment Report (AR5) increased this to 28 if calculated in the same way (100-year time horizon and no climate-carbon feedbacks in response to CH4 emissions), but also reports a value of 34 when these feedbacks are included (Myhre et al., 2013, p. 714). ...
... There is a sense though, that the inclusion of CH 4 was an afterthought, perhaps added in because it can be measured simultaneously with CO 2 on many gas chromatographs. Indeed, the significance of CH 4 as an agent of anthropogenic climate change was just beginning to come in to focus at the time (Hansen et al. 2000, Ramaswamy 2001), so its limited attention in streams and rivers is not necessarily surprising. Following these relatively quiet forays, two publications triggered a sudden increase in research activity during the past five years. ...
Streams and rivers can substantially modify organic carbon (OC) inputs from terrestrial landscapes, and much of this processing is the result of microbial respiration. While carbon dioxide (CO2) is the major end-product of ecosystem respiration, methane (CH4) is also present in many fluvial environments even though methanogenesis typically requires anoxic conditions that may be scarce in these systems. Given recent recognition of the pervasiveness of this greenhouse gas in streams and rivers, we synthesized existing research and data to identify patterns and drivers of CH4, knowledge gaps, and research opportunities. This included examining the history of lotic CH4 research, creating a database of concentrations and fluxes (MethDB) to generate a global-scale estimate of fluvial CH4 efflux, and developing a conceptual framework and using this framework to consider how human activities may modify fluvial CH4 dynamics. Current understanding of CH4 in streams and rivers has been strongly influenced by goals of understanding OC processing and quantifying the contribution of CH4 to ecosystem C fluxes. Less effort has been directed towards investigating processes that dictate in situ CH4 production and loss. CH4 makes a meager contribution to watershed or landscape C budgets, but streams and rivers are often significant CH4 sources to the atmosphere across these same spatial extents. Most fluvial systems are supersaturated with CH4 and we estimate an annual global emission of 26.8 Tg CH4, equivalent to ∼15-40% of wetland and lake effluxes, respectively. Less clear is the role of CH4 oxidation, methanogenesis, and total anaerobic respiration to whole ecosystem production and respiration. Controls on CH4 generation and persistence can be viewed in terms of proximate controls that influence methanogenesis (organic matter, temperature, alternative electron acceptors, nutrients) and distal geomorphic and hydrologic drivers. Multiple controls combined with its extreme redox status and low solubility result in high spatial and temporal variance of CH4 in fluvial environments, which presents a substantial challenge for understanding its larger-scale dynamics. Further understanding of CH4 production and consumption, anaerobic metabolism, and ecosystem energetics in streams and rivers can be achieved through more directed studies and comparison with knowledge from terrestrial, wetland, and aquatic disciplines.
... By acting as cloud condensation nuclei (CCN) and/or ice nuclei, aerosols affect Earth's energy budget through the modification of cloud properties, which is often referred to as the aerosol indirect effect (AIE) (Twomey 1977;Albrecht 1989;Ramaswamy et al. 2001;Lohmann and Feichter 2005;Tao et al. 2012). A greater number of smaller cloud droplets formed in a dirty environment suppresses collision and coalescence processes and thus delays or inhibits rainfall. ...
It has been widely recognized that aerosols can modify cloud properties, but it remains uncertain how much the changes and associated variations in cloud radiative forcing are related to aerosol loading. Using 4 yr of A-Train satellite products generated from CloudSat, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite, and the Aqua satellite, the authors investigated the systematic changes of deep cloud properties and cloud radiative forcing (CRF) with respect to changes in aerosol loading over the entire tropics. Distinct correlations between CRF and aerosol loading were found. Systematic variations in both shortwave and longwave CRF with increasing aerosol index over oceans and aerosol optical depth over land for mixed-phase clouds were identified, but little change was seen in liquid clouds. The systematic changes are consistent with the microphysical effect and the aerosol invigoration effect. Although this study cannot fully exclude the influence of other factors, attempts were made to explore various possibilities to the extent that observation data available can offer. Assuming that the systematic dependence originates from aerosol effects, changes in CRF with respect to aerosol loading were examined using satellite retrievals. Mean changes in shortwave and longwave CRF from very clean to polluted conditions ranged from -192.84 to -296.63 W m(-2) and from 18.95 to 46.12 W m(-2) over land, respectively, and from -156.12 to -170.30 W m(-2) and from 6.76 to 11.67 W m(-2) over oceans, respectively.
... Ozone, especially stratospheric ozone, is a greenhouse gas influencing the climate. It has been estimated that the past increase in the tropospheric abundance of ozone may have provided the third largest increase in direct radiative forcing since the preindustrial era (123,124). The most significant meteorological variables directly affected by climate change are temperature and specific humidity. ...
Ozone is a highly oxidative compound formed in the lower atmosphere from gases (originating to a large extent from anthropogenic sources) by photochemistry driven by solar radiation. Owing to its highly reactive chemical properties, ozone is harmful to vegetation, materials and human health. In the troposphere, ozone is also an efficient greenhouse gas. This report summarizes the results of a multidisciplinary analysis aiming to assess the effects of ozone on health. The analysis indicates that ozone pollution affects the health of most of the populations of Europe, leading to a wide range of health problems. The effects include some 21 000 premature deaths annually in 25 European Union countries on and after days with high ozone levels. Current policies are insufficient to significantly reduce ozone levels in Europe and their impact in the next decade
... In calculating greenhouse gas forcing I used concentrations taken from the data provided by the representative concentration pathways, which were developed for CMIP5 (PRE2005_MIDYR_CONC.DAT). Concentrations for CO 2 , CH 4 , N 2 O, and all gases controlled under the Montreal Protocol (expressed as CFC-12 equivalent concentrations) are converted to a forcing using the simplified expressions provided in Ramaswamy et al. (2001). Stratospheric ozone (a negative forcing) and tropospheric ozone (a somewhat larger positive forcing) are not considered, and assumed to be offset by land-use changes, which are commensurate with the net ozone forcing, but of opposite sign (Myhre et al. 2013a). ...
Based on research showing that in the case of a strong aerosol forcing, this forcing establishes itself early in the historical record, a simple model is constructed to explore the implications of a strongly negative aerosol forcing on the early (pre-1950) part of the instrumental record. This model, which contains terms representing both aerosol-radiation and aerosol-cloud interactions, well represents the known time history of aerosol radiative forcing as well as the effect of the natural state on the strength of aerosol forcing. Model parameters, randomly drawn to represent uncertainty in understanding, demonstrate that a forcing more negative than -1.0Wm-2 is implausible, as it implies that none of the approximately 0.3-K temperature rise between 1850 and 1950 can be attributed to Northern Hemisphere forcing. The individual terms of the model are interpreted in light of comprehensive modeling, constraints from observations, and physical understanding to provide further support for the less negative (-1.0Wm-2) lower bound. These findings suggest that aerosol radiative forcing is less negative and more certain than is commonly believed.
... Wetlands are among the most important sources of atmospheric methane (Ramaswamy, 2001). However, spatio-temporal patterns of their methane emissions are poorly known (Ciais et al., 2013), which limits the accuracy to estimate methane emissions from wetlands (Kirschke et al., 2013 ). ...
... Wetlands are among the most important sources of atmospheric methane (Ramaswamy, 2001). However, spatio-temporal patterns of their methane emissions are poorly known (Ciais et al., 2013), which limits the accuracy to estimate methane emissions from wetlands (Kirschke et al., 2013 ). ...
... In the SCM the historical development in global concentration of CO 2 is calculated using a scheme based on (Joos et al., 1996). The CO 2 module uses an ocean mixed-layer pulse response function that characterizes the surface to deep ocean mixing in combination with a separate equation describing the air-sea exchange (Siegenthaler and Joos, 1992 (Ramaswamy et al., 2001) as well as concentration-forcing relations. ...
... Indirect effects of CH 4 on tropospheric O 3 and stratospheric H 2 O as well as effects on its own adjustment time, are taken into account. Parameterizations of tropospheric O 3 and OH as function of NO x , CO, VOC and CH 4 are taken from IPCC-TAR (Ramaswamy et al., 2001) as well as concentration-forcing relations. ...
... By comparing the atmospheric and oceanic processes between total AA effect (Figs. 5b,e,h,k,n) and direct AA effect alone (Figs. 5c,f,i,l,o), we suggest that the cooling effect of AAs is primarily caused by indirect aerosol effect through atmospheric processes. The indirect effects of sulfate aerosols make clouds brighter (first indirect effect) or longer lasting (second indirect effect) (e.g., Ramaswamy et al. 2001;Lohmann and Feichter 2005), thereby altering the ocean surface heat fluxes. This result demonstrates that the aerosol-cloud interaction is important in the Indian Ocean SST change, and also reveals an improvement from CMIP3 (largely neglecting the aerosol-cloud interaction) to CMIP5 models. ...
... By comparing the atmospheric and oceanic processes between total AA effect (Figs. 5b,e,h,k,n) and direct AA effect alone (Figs. 5c,f,i,l,o), we suggest that the cooling effect of AAs is primarily caused by indirect aerosol effect through atmospheric processes. The indirect effects of sulfate aerosols make clouds brighter (first indirect effect) or longer lasting (second indirect effect) (e.g., Ramaswamy et al. 2001;Lohmann and Feichter 2005), thereby altering the ocean surface heat fluxes. This result demonstrates that the aerosol-cloud interaction is important in the Indian Ocean SST change, and also reveals an improvement from CMIP3 (largely neglecting the aerosol-cloud interaction) to CMIP5 models. ...
... By comparing the atmospheric and oceanic processes between total AA effect (Figs. 5b,e,h,k,n) and direct AA effect alone (Figs. 5c,f,i,l,o), we suggest that the cooling effect of AAs is primarily caused by indirect aerosol effect through atmospheric processes. The indirect effects of sulfate aerosols make clouds brighter (first indirect effect) or longer lasting (second indirect effect) (e.g., Ramaswamy et al. 2001;Lohmann and Feichter 2005), thereby altering the ocean surface heat fluxes. This result demonstrates that the aerosol-cloud interaction is important in the Indian Ocean SST change, and also reveals an improvement from CMIP3 (largely neglecting the aerosol-cloud interaction) to CMIP5 models. ...
The Indian Ocean exhibits a robust basinwide sea surface temperature (SST) warming during the twentieth century that has affected the hydrological cycle, atmospheric circulation, and global climate change. The competing roles of greenhouse gases (GHGs) and anthropogenic aerosols (AAs) with regard to the Indian Ocean warming are investigated by using 17 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The increasing GHGs are considered to be one reason for the warming. Here model evidence is provided that the emission of AAs has slowed down the warming rate. With AAs, the warming trend has been slowed down by 0.34Kcentury21. However, the cooling effect is weakened when only the direct aerosol effect is considered. GHGs and AAs have competed with each other in forming the basinwide warming pattern as well as the equatorial east–west dipole warming pattern. Both the basinwide warming effect of GHGs and the cooling effect of AAs, mainly through indirect aerosol effect, are established through atmospheric processes via radiative and turbulent fluxes. The positive contributions of surface latent heat flux from atmosphere and surface longwave radiation due to GHGs forcing dominate the basinwide warming, while the reductions of surface shortwave radiation, surface longwave radiation, and latent heat flux from atmosphere associated with AAs induce the basinwide cooling. The positive Indian Ocean dipole warming pattern is seen in association with the surface easterly wind anomaly during 1870–2005 along the equator, which is produced by the increase of GHGs but weakened by AAs via direct aerosol effects.
... Atmospheric aerosols are recognized to have provided a substantial secular forcing of climate change over the industrial period, but of highly uncertain magnitude [Ramaswamy et al., 2001]; therefore it is essential that aerosol radiative forcing be well quantified and accurately represented in climate models to provide a sound basis for formulating policy regarding the reduction of anthropogenic influences on climate. Representations of aerosol processes in chemical transport models (CTMs) are necessary to develop and test such representations for use in climate models [National Research Council Panel on Aerosol Radiative Forcing and Climate, 1996]. ...
A high-resolution (1° × 1°, 27 vertical levels) Eulerian
chemical transport and transformation model for sulfate, SO2,
and related species driven by analyzed forecast meteorological data has
been run for the Northern Hemisphere for June-July 1997 and extensively
evaluated with observational data, mainly from air quality and
precipitation chemistry networks. For ˜5000 evaluations, 50% of
the modeled sulfate 24-hour mixing ratios were within a factor of 1.85
of the observations; 50% of ˜328 concurrent subgrid observations
were within a factor of 1.33. Much greater subgrid variation for 24-hour
SO2 mixing ratios (50% of ˜3552 observations were
within a factor of 2.32) reflects high variability of this primary
species; for ˜12600 evaluations, 50% of modeled mixing ratios were
within a factor of 2.54 of the observations. These results indicate that
a substantial fraction of the modeled and observed differences is due to
subgrid variation and/or measurement error. Sulfate mixing ratios are
identified by source type (biogenic, volcanic, and anthropogenic) and
production mechanism (primary and by gas-phase and aqueous-phase
oxidation). Examination of key diagnostics showed substantial variation
for the different types of sulfur, e.g., SO2 aqueous-phase
oxidation rates of 29-102% d-1 and sulfate residence times of
4-9 days. Volcanic emissions contributed 10% of the sulfate burden and
6% of emissions, because the elevated release allows large fractional
conversion of SO2 and long residence time. Biogenic
SO2 was generally at lower concentrations than
H2O2, resulting in efficient aqueous-phase
oxidation; this source type contributed 13% of emissions but only 5% of
sulfate burden. Anthropogenic sources were the dominant contributors to
sulfur emissions (80%) and sulfate burden (84%).
... Esto aumentó a 21 en el segundo informe de evaluación, de 1995, utilizado por el Protocolo de Kyoto (Schimel et al., 1996). En 2001 fue levantado a 23 en el tercer informe de evaluación (Ramaswamy et al., 2001) y luego a 25 en el cuarto informe de evaluación en 2007 (Forster et al., 2007). Desde entonces, un trabajo publicado en la revista Science que incluye efectos indirectos no considerados en el cuarto informe de evaluación ha estimado el valor en 34, con el rango de incertidumbre que se extiende hasta un valor de más de 40 (Shindell et al., 2009) ...
... Defined in this way, a positive TOA forcing indicates the addition of energy to the climate system (i.e. a radiative warming effect) whereas a negative effect indicates a net loss of energy (i.e. a radiative cooling effect). Note that for tropospheric aerosols that interact primarily with shortwave (SW) radiation, instantaneous forcing at the top-of-the atmosphere (TOA) and adjusted forcing as defined by the IPCC [Ramaswamy et al., 2001] are approximately equal [Hansen et al., 1997;Lohmann and Feichter, 2001]. In our GOAERO simulation, dust and sea-salt together have an instantaneous direct radiative effect (DRE) of -0.06 W m À2 . ...
The present-day climate response to aerosol direct and semi-direct
effects is investigated using the NASA Goddard Earth Observing System
version 5 (GEOS-5) atmospheric general circulation model. We focus our
investigation on aerosol-climate interactions by using either prognostic
aerosols from an online aerosol module or aerosols from a climatology
based on the prognostic aerosols. As found in previous studies, forcing
from all aerosols cools the land surface, warms the troposphere, and
impacts global mean circulation, affecting both the strength of the
Hadley cell and the zonal mean wind. Less absorbing natural aerosol
alone tends to have weaker impacts on global climate. We find that
removing the feedback of meteorology on aerosol distributions can
significantly impact the climate response depending on the parameter,
region, and season considered. Much of the differing climate response to
prognostic and prescribed aerosols occurs in regions remote from direct
aerosol forcing, such as in the stratosphere and the northern and
southern high latitudes. This suggests that aerosol-climate interactions
may induce remote dynamical responses to aerosol forcing in global
models. The largest effect of removing coupling is to enhance the
aerosol optical depth globally over the oceans. This enhancement is due
to the removal of the co-variability between aerosol mass and relative
humidity on sub-monthly timescales in the high humidity oceanic
environment.
Cyclone Fani, an extremely severe cyclone storm (ESCS) is one of the strongest cyclones in the Bay of Bengal (BoB) in recent decades and was responsible for the death of 90 people and the devastation of billions of dollars in Odisha. Many aspects of physical processes impact tropical cyclones. For the first time, the influence of aerosols on the structural and precipitation characteristics of the intense landfalling cyclone is investigated using high-resolution models over the Indian region. Two experiments using Weather Research and Forecast (WRF) are carried out i.e. without chemistry (CNT) and with chemistry (CHEM) in a nested domain fashion with 3 km resolution. The track and intensity forecast of CHEM is close to the observation compared to CNT during the landfall. In addition, the cyclone structure has been rapidly distorted in CNT due to early landfall (3 h prior) compared to observation, whereas CHEM has a realistic intensity, translational speed, structure and accurate landfall time. It is found that the CNT has a large overestimation of rainfall (> 300 mm) due to the presence of anomalously high cloud water and cloud ice compared to CHEM (250–300 mm), which has a closer match with observations. In general, it is also noted that the moisture source/sink Qm has more contribution than cloud source/sink Qc in rain for both simulations. However, the CNT has a high contribution in Qm compared to CHEM due to overestimated moisture and intense vertical and horizontal advection. The intrusion of dust aerosol at the lower level leads to a higher boundary layer and radiative heating facilitating a more stable environment leading to suppression of moisture and weaker updrafts resulting in a realistic intensity and rainfall during landfall in CHEM. These findings have significant implications for aerosol re-distribution and how it affects precipitation and structural patterns of the cyclone.
We studied how different thinning regimes and initial age structures of a Norway spruce (Picea abies (L.) Karst.) forest landscape affect the radiative forcing of forest biomass production and use. We considered the effects of forest carbon sequestration, substitution of materials and fossil fuels with forest biomass, and timber use efficiency. The initial age structures of our hypothetical forest landscapes in the middle boreal zone in Finland were young, middle-aged, and mature. Forest landscapes were thinned using either the current thinning recommendations (baseline) or maintaining 20% higher or 20% lower stocking over the 80-year study period. We employed forest ecosystem model simulations together with a life cycle assessment tool. The highest carbon sequestration was obtained by maintaining higher stocking in the landscapes. The initially middle-aged and mature age structures resulted in the strongest cooling of the climate in the first three decades of the simulation, but the highest cooling was found in the young age structure. However, radiative forcing was less sensitive to the thinning than to the substitution or timber use efficiency. Our results indicate that modeled climate impacts are affected by both initial age structure and forest management, which should be considered when generalizing the climate change mitigation potential of forests and forestry.
The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2–4 at atmospheric CO2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO2 levels reach threshold levels.
Retrieval of cloud parameters is fundamental for descriptions of the cloud process in weather and cloud models, and is also the base for theoretical and applicational investigations on weather modification, aerosol-cloud-precipitation interaction, cloud-radiative climate effects, and so on. However, it is still difficult to obtain full information of cloud parameters over a wide area under the current level of science and technology. Luckily, parameters at the top of clouds can be retrieved with the satellite spectrum remote sensing, which is useful in obtaining global cloud properties. In this paper, cloud parameters retrieved by the bispectral reflectance (BSR) method and other methods developed on the basis of the BSR are briefly summarized. Recent advances in studies on the indirect effects of aerosol on cloud parameters are reviewed. The relationships among cloud parameters and precipitation intensity, type, and structure are elaborated on, based upon the pixel-level merged datasets derived from daily measurements of precipitation radar and visible and infrared scanner, together with cloud parameters retrieved by the BSR. It is revealed that cloud particle effective radius and liquid water path near cloud tops are effective to identify the thickness and intensity of convective precipitating clouds. Furthermore, the differences in cloud parameters and precipitation intensity for precipitating and non-precipitating clouds over land and ocean are compared in this paper.
We used a fully coupled chemistry–climate model (version 3 of the Whole Atmosphere Community Climate Model, WACCM3) to investigate the effect of methane (CH4) emission increases, especially in East Asia and North America, on atmospheric temperature, circulation and ozone (O3). We show that CH4 emission increases strengthen westerly winds in the Northern Hemisphere midlatitudes, accelerate the Brewer–Dobson (BD) circulation, and cause an increase in the mass flux across the tropopause. However, the BD circulation in the tropics between 10°S and 10°N at 100 hPa weakens as CH4 emissions increase in East Asia and strengthens when CH4 emissions increase in North America. When CH4 emissions are increased by 50% in East Asia and 15% globally, the stratospheric temperature cools by up to 0.15 K, and the stratospheric O3 increases by 45 ppbv and 60 ppbv, respectively. A 50% increase of CH4 emissions in North America (with an amplitude of stratospheric O3 increases by 60 ppbv) has a greater influence on the stratospheric O3 than the same CH4 emissions increase in East Asia. CH4 emission increases in East Asia and North America reduce the concentration of tropospheric hydroxyl radicals (4% and 2%, respectively) and increase the concentration of mid-tropospheric O3 (5% and 4%, respectively) in the Northern Hemisphere midlatitudes. When CH4 emissions increase in East Asia, the increase in the tropospheric O3 concentration is largest in August. When CH4 emissions increase in North America, the increase in the O3 concentration is largest in July in the mid-troposphere, and in April in the upper troposphere. © 2015, Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.
Vertically integrated anthropogenic aerosol mass concentration Ma and low-level water cloud properties (optical depth τ, effective particle radius re, and columnar droplet number Nc) were correlated over east Asia to elucidate human-induced effects on low-cloud properties. Aerosol and cloud properties were obtained from numerical simulations and satellite observations, respectively. Monthly averages of geographical matches between collocated Ma and cloud properties for three seasons showed that as Ma increased, τ and Nc increased and re, decreased, which is consistent with the Twomey effect. Their changing rates became less steep when Ma was large. However, the importance of a dynamical effect was also suggested. A comparison of different cloud top heights revealed that values of τ and re of middle and lower clouds followed those of the total water cloud cases and reflected vertical characteristics.
Tradução de:
Fearnside, P.M. 2015. Emissions from tropical hydropower and the IPCC. Environmental Science & Policy (in press). doi: 10.1016/j.envsci.2015.03.002
RESUMO As emissões de hidrelétricas tropicais são subestimadas em inventários nacionais de gases de efeito estufa no âmbito da Convenção-Quadro das Nações Unidas sobre Mudança do Clima (UNFCCC), dando-lhes um papel em minar a eficácia de limites, ainda não decididos, sobre emissões. As emissões de hidrelétricas tropicais são também em grande parte, deixadas fora do Relatório Especial sobre Fontes Renováveis de Energia e Mitigação das Mudanças Climáticas, do Painel Intergovernamental sobre Mudanças Climáticas (IPCC), e foram excluídas de uma revisão das orientações do IPCC sobre zonas úmidas. O papel das hidrelétricas em inventários de emissões e na mitigação tem sido sistematicamente ignorado. Palavras-chave: Amazônia; aquecimento global; emissões de gases de efeito estufa; hidrelétricas; metano; mitigação Emissões de barragens tropicais Barragens da Amazônia produzem gases de efeito estufa, especialmente durante seus primeiros dez anos de operação (e. publicados para emissões de hidrelétricas variam muito, mas a maior parte desta variação pode ser explicada por diferenças conhecidas entre as barragens em questão, por omissões conhecidas e por problemas na metodologia de medição, particularmente para os valores baixos. A existência de incerteza tem sido usada repetidamente como justificativa para não levar as emissões de hidrelétricas em conta. Entre os exemplos desta prática é o atual conjunto de diretrizes do Painel Intergovernamental sobre Mudança Climática (IPCC) para os inventários nacionais, que optou por não para fornecer valores padrão (default) para as grandes fontes de emissões de hidrelétricas através de desgaseificação nas turbinas, de ebulição (bolhas) da superfície do reservatório e de ebulição e difusão no rio a jusante da barragem (IPCC, 2006, Vol. 4, Apêndice 3). 1. Barragens nos relatórios e diretrizes do IPCC
The areal extent of the Maritime Continent (the islands of Indonesia and surrounding region) has grown larger by ~60% since 5 Ma. We argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible. First, because rainfall over the islands of the Maritime Continent not only is heavier than that over the adjacent ocean, but also correlates with the strength of the Walker Circulation, the growth of the Maritime Continent since 5 Ma may have contributed to the cooling of the eastern tropical Pacific since that time. Scaling relationships between the strength of the Walker Circulation and rainfall over the islands of the Maritime Continent and between sea-surface temperature (SST) of the eastern tropical Pacific and the strength of easterly wind stress suggest that the increase in areal extent of islands would lead to a drop in that SST of 0.75°C. Although only a fraction of the 3-4°C decrease in SSTs between the eastern and western tropical Pacific, the growth of the Maritime Continent may have strengthened the Walker Circulation, increased the east-west temperature gradient across the Pacific, and thereby enabled ice sheets to wax and wane over Canada since 3 Ma. Second, because the weathering of basaltic rock under warm, moist conditions extracts CO2 from the atmosphere more rapidly than weathering of other rock or of basalt under cooler or drier conditions, the increase in weathering due to increasing area of basalt in the Maritime Continent may have drawn down enough CO2 from the atmosphere to affect global temperatures. Simple calculations suggest that increased weathering of basalt might have lowered global temperatures by 0.25°C, possibly important for the overall cooling.
Important forest ecosystem services are the provision of a habitat for a diversity of plants and wildlife (habitat service), pollutant filtering relevant for an adequate water quality (regulating service) and wood production with the related carbon (C) storage (provisioning/regulating service). Nitrogen (N) deposition affects these ecosystem services as it has an impact on: (i) the habitat for wild plants, reducing plant species diversity, (ii) water/soil quality by its impact on acidity (pH) and on the soil accumulation and leaching of N as nitrate, aluminium (Al) and metals to ground water and surface water and (iii) net primary production and C sequestration. In this chapter, we describe the application of the Very Simple Dynamic (VSD) model, extended with relationships between nitrogen (N) deposition and greenhouse gas emissions, on a European-wide scale to quantify the impact of N deposition on these forest ecosystem services. This includes: (i) potential impacts of N deposition on plant species diversity in terms of excess N deposition compared to critical loads for N, (ii) excess nitrate (NO3) and Al concentrations in leachate to groundwater and surface water compared to critical limits, (iii) soil acidification, in terms of the depletion of the pools of base cations (BC) and Al, and (iv) C sequestration and related emissions of the greenhouse gases carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Results show that the N deposition reduction measures that have been taken since 1980 have led to a reduction between 10 and 15 % in the areas exceeding critical N loads and critical limits for NO3 and Al in groundwater or surface water, but the estimated CO2 uptake is nearly 20 % lower under a reduced N deposition scenario as compared to a constant 1980 N deposition scenario. The N induced N2O emissions however counteract the N induced C sequestration.
Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.
Concurrent changes in climate, atmospheric nitrogen (N) deposition, and increasing levels of atmospheric carbon dioxide (CO2) affect ecosystems in complex ways. The DayCent-Chem model was used to investigate the combined effects of these human-caused drivers of change over the period 1980–2075 at seven forested montane and two alpine watersheds in the United States. Net ecosystem production (NEP) increased linearly with increasing N deposition for six out of seven forested watersheds; warming directly increased NEP at only two of these sites. Warming reduced soil organic carbon storage at all sites by increasing heterotrophic respiration. At most sites, warming together with high N deposition increased nitrous oxide (N2O) emissions enough to negate the greenhouse benefit of soil carbon sequestration alone, though there was a net greenhouse gas sink across nearly all sites mainly due to the effect of CO2 fertilization and associated sequestration by plants. Over the simulation period, an increase in atmospheric CO2 from 350 to 600 ppm was the main driver of change in net ecosystem greenhouse gas sequestration at all forested sites and one of two alpine sites, but an additional increase in CO2 from 600 to 760 ppm produced smaller effects. Warming either increased or decreased net greenhouse gas sequestration, depending on the site. The N contribution to net ecosystem greenhouse gas sequestration averaged across forest sites was only 5–7 % and was negligible for the alpine. Stream nitrate (NO3−) fluxes increased sharply with N-loading, primarily at three watersheds where initial N deposition values were high relative to terrestrial N uptake capacity. The simulated results displayed fewer synergistic responses to warming, N-loading, and CO2 fertilization than expected. Overall, simulations with DayCent-Chem suggest individual site characteristics and historical patterns of N deposition are important determinants of forest or alpine ecosystem responses to global change.
O C fotossintetizado adicionado ao solo pelos resíduos vegetais (C-resíduo), as emissões de C na forma de dióxido de carbono (C-CO2) e o estoque de C orgânico do solo (C-solo) são componentes do ciclo deste elemento no sistema solo-planta-atmosfera. O efeito de práticas de manejo de solo sobre esses componentes necessita de melhor entendimento, visando à identificação de um sistema com potencial de reter C atmosférico no solo e contribuir para a mitigação do aquecimento global. Neste estudo, as emissões de C-CO2, o estoque de C e as adições de C pelos resíduos vegetais foram avaliados em experimento de longa duração (18anos), localizado em Eldorado do Sul (RS). O quociente C-CO2/(C-resíduo + C-solo) foi proposto como índice da capacidade de sistemas de preparo e de cultura em conservar C no solo (ICC). A emissão de C-CO2 foi medida durante 17 meses; a quantidade de C-resíduo foi estimada com base em amostragens da massa de plantas de cobertura de inverno e no índice de colheita do milho; e o estoque de C-solo, avaliado na camada de 00,2m do solo submetido aos sistemas de preparo convencional (PC) e plantio direto (PD), associados às sucessões de aveia (Avena strigosa Schreb)/milho (Zea mays L.) (A/M) e ervilhaca comum (Vicia sativa L.)/milho (E/M). Com objetivo de avaliar a relação das emissões de C-CO2 com fatores ambientais, foram monitoradas a temperatura a 0,05m de profundidade e a umidade gravimétrica do solo nas camadas de 00,05; 0,050,1; e 0,10,2m. Em comparação ao estoque de C-solo no início do experimento (33,4tha-1), o balanço foi negativo no solo em PC (-0,31tha-1ano-1 no A/M e -0,10tha-1ano-1 no E/M) e positivo no solo em PD (0,15tha-1ano-1 ) apenas quando associado ao sistema E/M, o qual apresentou maior aporte de resíduos. As taxas mensais médias das emissões variaram entre 0,27gm-2 de C-CO2 no inverno (média das temperaturas mínimas = 8°C) e 1,36gm-2 de C-CO2 no verão (média das temperaturas máximas = 38º C), que se relacionaram com a temperatura do solo (r>0,85). A emissão total de C-CO2 no período variou entre 3,6 e 4,0tha-1 de C-CO2, não tendo sido verificada diferença significativa entre os sistemas de preparo de solo e de cultura. Entretanto, o ICC evidenciou que o potencial dos sistemas de manejo em conservar C no solo aumentou na ordem PC A/M < PC E/M < PD A/M < PD E/M. As condições menos oxidativas contribuíram para o balanço positivo de C no solo em plantio direto, característica que é potencializada pela utilização de sistemas de cultura com leguminosas como plantas de cobertura, que favorecem o acúmulo de C no solo por permitirem maior produção de massa das gramíneas cultivadas em sucessão, devido ao fornecimento de N.
The climate feedback framework partitions the radiative response to climate forcing into con-tributions from individual atmospheric processes. The goal of this study is to understand the closure of the energy budget in as much detail and precision as possible, within as clean an experimental set-up as possible. For an aquaplanet simulation under perpetual equinox conditions, we account for rapid tropospheric adjustments to CO 2 and diagnose radiative kernels for this precise model set-up. We characterize the meridional structure of feedbacks, energy transport, and nonlinearities in controlling the local climate response. Our results display a combination of strongly positive subtropical feedbacks and polar amplification. These two factors imply a critical role for transport and nonlinear effects, with the latter acting to substantially reduce global climate sensitivity. At the hemispheric scale, a rich picture emerges: heat flux divergence away from positive feedbacks in the tropics; nonlinearities that cool the tropics and warm the high-latitudes; and strong ice-line feedbacks that drive further amplification of polar warming. These results have implications for regional climate predictability, by providing an indication of 1) how spatial patterns in feedbacks combine to affect both the local and nonlocal climate response, and 2) how constraining uncertainty in those feedbacks may constrain the climate response.
Radiative feedbacks influence Earth's climate response to orbital forcing, amplifying some aspects of the response while damping others. To better understand this relationship, the GFDL Climate Model, version 2.1 (CM2.1), is used to perform idealized simulations in which only orbital parameters are altered while ice sheets, atmospheric composition, and other climate forcings are prescribed at preindustrial levels. These idealized simulations isolate the climate response and radiative feedbacks to changes in obliquity and longitude of the perihelion alone. Analysis shows that, despite being forced only by a redistribution of insolation with no global annual-mean component, feedbacks induce significant global-mean climate change, resulting in mean temperature changes of -0.5 K in a lowered obliquity experiment and +0.6 K in a NH winter solstice perihelion minus NH summer solstice perihelion experiment. In the obliquity experiment, some global-mean temperature response may be attributable to vertical variations in the transport of moist static energy anomalies, which can affect radiative feedbacks in remote regions by altering atmospheric stability. In the precession experiment, cloud feedbacks alter the Arctic radiation balance with possible implications for glaciation. At times when the orbital configuration favors glaciation, reductions in cloud water content and low-cloud fraction partially counteract changes in summer insolation, posing an additional challenge to understanding glacial inception. Additionally, several systems, such as the Hadley circulation and monsoons, influence climate feedbacks in ways that would not be anticipated from analysis of feedbacks in the more familiar case of anthropogenic forcing, emphasizing the complexity of feedback responses.
NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) archives and distributes pioneering collections of data on atmospheric greenhouse gases. In September of 2012, the Atmospheric Infrared Sounder (AIRS) marked a decade of tropospheric observations of carbon dioxide (CO2). Most recently, the Atmospheric CO2 Observations from Space (ACOS) project and GES DISC released CO2 retrievals derived from radiances observed by the Japanese Greenhouse gases Observing SATellite (GOSAT) satellite, launched in 2009. In this letter, we present the most recent estimates of decadal mid-tropospheric trends of CO2 from AIRS, as well as the most recent status of the total column-average distribution of CO2 from ACOS. We also demonstrate that significant discrepancies still exist in the global distribution of observed and modeled column amounts of CO2 using the CO2 retrievals from the ACOS project.
Emissions of greenhouse gases and air pollutants from megacities impact the climate. The long-lived greenhouse gases CO 2, CH 4 and N 2O as well as climate-active pollutants such as NO x, VOC and particulate matter (PM) are all emitted from megacities. NO x and VOC contribute to tropospheric ozone formation and affect the lifetime of long-lived greenhouse gases. Anthropogenic aerosols include sulphate, black carbon (BC) and particulate organic matter (POM). Aerosols impact climate directly (absorption, backscattering) and also have indirect (cloud) effects. We assess the climate impact of megacity emissions with the Met Office Hadley Centre Earth System Model HadGEM2 applying an "annihilation" scenario in which the emissions at megacities are entirely removed. Generally, the contribution of megacities to global pollutant emissions is on the order of 2-5% of the total global annual anthropogenic base emission flux. The impact of megacity climate-active pollutants is assessed via an annual mean top-of-atmosphere direct radiative forcing (AMTOA-DRF) from long-lived GHG as well as ozone, methane and aerosols. In this simulations the long-lived component (CO 2, CH 4 and N 2O) contributes a positive TOA-DRF of +120.0, +28.4 and +3.3mWm -2, respectively, under present-day conditions. Climate-active pollutants (NO x, VOC) contribute an AMTOA-DRF of +5.7±0.02mWm -2 from an increase in the ozone burden -1.9±0.04mWm -2, -6.1±0.21mWm -2 from the aerosol AMTOA-DRF in the short-wave spectrum and +1.5±0.01mWm -2 from aerosol in the long-wave spectrum. The combined AMTOA-DRF from all climate-active pollutants is slightly negative at -0.8±0.24mWm -2 and the total AMTOA-DRF amounts to +150.9±0.24mWm -2. Under future conditions (2050s) the total AMTOA-DRF from long-lived GHG is found to profoundly increase to +322.6mWm -2 while the total AMTOA-DRF from climate-active pollutants turns positive and decreases slightly to +0.5±0.09mWm -2 yielding a combined AMTOA-DRF of +323.1±0.09mWm -2 in the future. It is apparent that under the given emission scenarios the radiative forcing from long-lived GHG, particularly CO 2, by far dominates the impact of megacities on climate.
At the regional scale, enhanced climatic variability masks the role of external forcings. It has been shown that a consistent attribution of regional temperature behaviour can be achieved just by considering circulation patterns as driving elements. Here we address this question: is the role of external forcings completely hidden in the changes of circulation patterns (eventually induced by them), or is there evidence of a more direct role for these forcings? Performing a fully nonlinear analysis shows that a direct role for anthropogenic forcings can be detected also at this regional scale, while natural forcings do not seem to influence temperature behaviour.
Rhodium has been proved to possess unique reactivity to convert NOx into N2 with high conversion efficiency and selectivity. In this study, we have carried out DFT calculations on the reaction mechanism in the reduction of NO by CO on the surface of the Rh7+ cluster. The calculated results suggest that the reaction proceeds via three steps. First, the NO and CO are adsorbed on the Rh7+ cluster, then the adsorbed NO decomposes to N and O atoms. The O atom reacts with the adsorbed CO leading to the formation of CO2 molecule. Second, another NO is adsorbed on the rhodium cluster and decomposes to N and O atoms, then the two N atoms couple with each other to yield N2 molecule. Finally, the second CO can be adsorbed on the Rh1 or Rh7 atom of the Rh7+ cluster and oxidized to CO2 molecule. On the basis of present calculations from gas-phase Gibbs free energy profiles, the reaction path related to CO adsorption on the Rh7 atom is energetically more favorable. The second adsorbed NO generating N and O atoms in the second step is the rate-limiting step of whole catalytic cycle. The high activation barrier (TS67) of 56.6 kcal/mol can be driven by large exergonic reaction. Our work would provide some valuable fundamental insights into the reaction mechanism between NO and CO on the rhodium surface, which is vitally important to decrease NO emissions in automotive exhaust gas.
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