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Amazon Tipping Point
In the 1970s, Brazilian scientist Eneas Salati shattered
the long held dogma that vegetation is simply the
consequence of climate and has no influence on cli-
mate whatsoever (1). Using isotopic ratios of oxygen
in rainwater samples collected from the Atlantic to
the Peruvian border, he was able to demonstrate un-
equivocally that the Amazon generates approximately
half of its own rainfall by recycling moisture 5 to 6 times
as airmasses move from the Atlantic across the basin to
the west.
From the start, the demonstration of the hydrological
cycle of the Amazon raised the question of how much
deforestation would be required to cause the cycle to de-
grade to the point of being unable to support rain forest
ecosystems.
High levels of evaporation and transpiration that forests
produce throughout the year contribute to a wetter at-
mospheric boundary layer than would be the case with
non-forest.This surface-atmosphere coupling is more im-
portant where large-scale factors for rainfall formation
are weaker, such as in central and eastern Amazonia. Near
the Andes, the impact of at least modest deforestation is
less dramatic because the general ascending motion of
airmasses in this area induces high levels of rainfall in
addition to that expected from local evaporation and
transpiration.
Where might the tipping point be for deforestation-
generated degradation of the hydrological cycle? The
very first model to examine this question (2) showed that
at about 40% deforestation, central, southern and eastern
Amazonia would experience diminished rainfall and a
lengthier dry season, predicting a shift to savanna vegeta-
tion to the east.
Moisture from the Amazon is important to rainfall and
human wellbeing because it contributes to winter rainfall
for parts of the La Plata basin, especially southern Paraguay,
southern Brazil, Uruguay and central-eastern Argentina;
in other regions, the moisture passes over the area, but does
not precipitate out. Although the amount contributing
to rainfall in southeastern Brazil is smaller than in other
areas, even small amounts can be a welcome addition to
urban reservoirs.
The importance of Amazon moisture for Brazilian ag-
riculture south of the Amazon is complex but not trivial.
Perhaps most important is the partial contribution of dry
season Amazon evapotranspiration to rainfall in south-
eastern South America. Forests maintain an evapotranspira-
tion rate year-round, whereas evapotranspiration in pastures
is dramatically lower in the dry season. As a consequence,
models suggest a longer dry season after deforestation.
In recent decades, new forcing factors have impinged
on the hydrological cycle: climate change and widespread
use of fire to eliminate felled trees and clear weedy veg-
etation. Many studies show that in the absence of other
contributing factors, 4 degrees Celsius of global warming
would be the tipping point to degraded savannas in most
of the central, southern, and eastern Amazon. Widespread
use of fire leads to drying of surrounding forest and greater
vulnerability to fire in the subsequent year.
We believe that negative synergies between deforesta-
tion, climate change, and widespread use of fire indicate
a tipping point for the Amazon system to flip to non-
forest ecosystems in eastern, southern and central Amazonia
at 20-25% deforestation.
The severity of the droughts of 2005, 2010 and 2015-16
could well represent the first flickers of this ecological
tipping point. These events, together with the severe floods
of 2009, 2012 (and 2014 over SW Amazonia), suggest that
the whole system is oscillating. For the last two decades
the dry season over the southern and eastern Amazon
has been increasing. Large scale factors such as warmer
sea surface temperatures over the tropical North Atlantic
also seem to be associated with the changes on land.
We believe that the sensible course is not only to strictly
curb further deforestation, but also to build back a margin
of safety against the Amazon tipping point, by reducing
the deforested area to less than 20%, for the commonsense
reason that there is no point in discovering the precise
tipping point by tipping it. At the 2015 Paris Conference
of the Parties, Brazil committed to 12 million ha of re-
forestation by 2030. Much or most of this reforestation
should be in southern and eastern Amazonia. The hydro-
logical cycle of the Amazon is fundamental to human well-
being in Brazil and adjacent South America.
– Thomas E. Lovejoy and Carlos Nobre
REFERENCES
1. E. Salati, A. Dall ‘Ollio, E. Matsui, J. R. Gat, Recycling of Water in the Amazon,
Brazil: an isotopic study. Water Resour. Res. 15, 1250–1258 (1979).
2. G. Sampaio,C. A. Nobre, M. H. Costa, P. Satyamurty, B. S. Soares-Filho,
M. Cardoso, Regional climate change over eastern Amazonia caused by pasture
and soybean cropland expansion. Geophys. Res. Lett. 34, L17709 (2007).
10.1126/sciadv.aat2340
Citation: T. E. Lovejoy, C. Nobre, Amazon Tipping Point. Sci. Adv. 4, eaat2340 (2018).
Thomas E. Lovejoy is
University Professor
in the Department of
Environmental Science
and Policy at George
Mason University. Email:
tlovejoy@unfoundation.org
Carlos Nobre is a Member
of the Brazilian Academy
of Sciences and Senior
Fellow of World Resources
Institute Brazil.
on February 22, 2018http://advances.sciencemag.org/Downloaded from
Amazon Tipping Point
Thomas E. Lovejoy and Carlos Nobre
DOI: 10.1126/sciadv.aat2340
(2), eaat2340.4Sci Adv
ARTICLE TOOLS http://advances.sciencemag.org/content/4/2/eaat2340
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... For example, degradation from timber extraction, extreme droughts, and edge effects alter the forest micro-climate, making future fires more likely (29). The feedbacks between Amazon forest degradation and regional climate change are particularly relevant for determining the likelihood of an Amazon tipping point (118,119). ...
... Preventing further deforestation remains a key objective for stabilizing the climate system, preserving biodiversity, and ensuring sustainable development; deforestation is itself a major driver of greenhouse gas emissions and biodiversity loss and a driver of several forms of degradation (Fig. 1). The integrity of the basin also depends on maintaining sufficient forest cover (119). Preventing additional degradation will also benefit from the conditions required to curb deforestation, such as the strengthening of land tenure, environmentoriented credit concession, and the provision of sustainable income and livelihood alternatives that can attenuate social inequalities (124). ...
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Approximately 2.5 × 106 square kilometers of the Amazon forest are currently degraded by fire, edge effects, timber extraction, and/or extreme drought, representing 38% of all remaining forests in the region. Carbon emissions from this degradation total up to 0.2 petagrams of carbon per year (Pg C year-1), which is equivalent to, if not greater than, the emissions from Amazon deforestation (0.06 to 0.21 Pg C year-1). Amazon forest degradation can reduce dry-season evapotranspiration by up to 34% and cause as much biodiversity loss as deforestation in human-modified landscapes, generating uneven socioeconomic burdens, mainly to forest dwellers. Projections indicate that degradation will remain a dominant source of carbon emissions independent of deforestation rates. Policies to tackle degradation should be integrated with efforts to curb deforestation and complemented with innovative measures addressing the disturbances that degrade the Amazon forest.
... It is widely accepted that the Amazon Forest is a potential tipping element in the global climate system (Lenton et al., 2008;Lovejoy and Nobre, 2018;Boulton et al., 2022). Recently, the IPCC assessed a dieback of Amazon Forest during the 21 st century as a low-probability event (Canadell et al., 2021, WGI AR6 Chapter 5), and there is medium confidence in insignificant net changes in vegetation carbon storage in tropical regions (Table 4.10 in Lee et al., 2021, WGI AR6 Chapter 4). ...
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Received 7 May 2007; revised 7 August 2007; accepted 9 August 2007; published 13 September 2007. (1) Field observations and numerical studies revealed that large scale deforestation in Amazonia could alter the regional climate significantly, projecting a warmer and somewhat drier post-deforestation climate. In this study we employed the CPTEC-INPE AGCM to assess the effects of Amazonian deforestation on the regional climate, using simulated land cover maps from a business-as-usual scenario of future deforestation in which the rainforest was gradually replaced by degraded pasture or by soybean cropland. The results for eastern Amazonia, where changes in land cover are expected to be larger, show increase in near-surface air temperature, and decrease in evapotranspiration and precipitation, which occurs mainly during the dry season. The relationship between precipitation and deforestation shows an accelerating decrease of rainfall for increasing deforestation for both classes of land use conversions. Continued expansion of cropland in Amazonia is possible and may have important consequences for the sustainability of the region's remaining natural vegetation. Citation: Sampaio, G., C. Nobre, M. H. Costa, P. Satyamurty, B. S. Soares-Filho, and M. Cardoso (2007), Regional climate change over eastern Amazonia caused by pasture and soybean cropland expansion, Geophys. Res. Lett., 34, L17709,
  • T E Lovejoy
  • C Nobre
Citation: T. E. Lovejoy, C. Nobre, Amazon Tipping Point. Sci. Adv. 4, eaat2340 (2018).
Recycling of Water in the Amazon, Brazil: an isotopic study
  • E Salati
  • A Ollio
  • E Matsui
  • J R Gat
  • Salati E.