Editing IPCC:AR6/WGI/Chapter-8 (section)

==== 8.6.2.1 Amazon Deforestation and Drying ====

<div id="h3-50-siblings" class="h3-siblings"></div>

The Amazon forest plays an active role in driving atmospheric moisture transport and generating precipitation in the South American region ( SRCCL; Drumond et al. , 2014; Poveda et al. , 2014; Yin et al. , 2014; Staal et al. , 2018, 2020; Agudelo et al. , 2019; Espinoza et al. , 2019) . This close association between the land surface and the water cycle makes the Amazon a potential hotspot for abrupt change ( [[#Torres--2014|Torres and Marengo, 2014]] ). Both deforestation and drying are projected to increase by 2100, resulting in a worst-case scenario of up to a 50% loss in forest cover by 2050 (Soares-Filho et al. , 2006; Boisier et al. , 2015; ter Steege et al. , 2015; Gomes et al. , 2019) . Deforestation in the Amazon also raises the probability of catastrophic fires ( [[#Brando--2014|Brando et al., 2014]] ). The combination of deforestation, drier conditions, and increased fire can push the rainforest ecosystem past a tipping point, beyond which there is rapid land surface degradation, a sharp reduction in atmospheric moisture recycling, an increase in the fraction of precipitation that runs off, and a further shift towards a drier climate (Staal et al. , 2015; Boers et al. , 2017; Zemp et al. , 2017; Ruiz-Vásquez et al. , 2020) . A rapid drop in precipitation has a direct impact on river flows, driving basin-scale shifts from a regulated to unregulated state ( [[#Salazar--2018|Salazar et al., 2018]] ). Regional climate modeling experiments confirm that increased deforestation leads to a drier climate, although not all models show a true tipping point, at least under present-day climatic conditions ( [[#Lejeune--2015|Lejeune et al., 2015]] ; [[#Spracklen--2015|Spracklen and Garcia-Carreras, 2015]] ).

In AR5, some simulations using a coupled climate–carbon cycle model exhibited an abrupt dieback of the Amazon forest in future climate scenarios ( [[#Oyama--2003|Oyama and Nobre, 2003]] ; [[#Cox--2004|Cox et al., 2004]] ; [[#Malhi--2008|Malhi et al., 2008]] ).However, subsequent work demonstrated that abrupt Amazon dieback does not occur consistently across, or even within, Earth system models ( [[#Lambert--2013|Lambert et al., 2013]] ; [[#Boulton--2017|Boulton et al., 2017]] ). The occurrence of dieback is highly dependent on both how dry the simulated climate is in the present day ( [[#Malhi--2009|Malhi et al., 2009]] ) as well as the representation of forest structure and competitive dynamics ( [[#Levine--2016|Levine et al., 2016]] ). Models with a low diversity of plant characteristics and types have a higher tendency for abrupt change ( [[#Sakschewski--2016|Sakschewski et al., 2016]] ). Abrupt shifts and ecosystem disruptions can occur on the sub-regional level ( [[#Pires--2013|Pires and Costa, 2013]] ), highlighting the need for higher-resolution modelling studies. Since AR5, CMIP6 projections suggest that a tipping point in the Amazon system may be crossed on a local or regional scale ( [[#Staal--2020|Staal et al., 2020]] ) but continue to be highly dependent on model biases in precipitation and the simulation of the land surface. Consequently, the timing, and probability, of an abrupt shift remains difficult to ascertain.

In summary, while there is a strong theoretical expectation that Amazon drying and deforestation can cause a rapid change in the regional water cycle, currently there is ''limited'' model ''evidence'' to verify this response, hence there is ''low confidence'' that such a change will occur by 2100.

<div id="8.6.2.2" class="h3-container"></div>

<span id="greening-of-the-sahara-and-the-sahel"></span>