Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.10.5 Tropical Forests ====

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Tropical forests, which are among the world’s most biologically diverse ecosystems, are essentially located in Central and South America, Africa and South East Asia (AR6 WGII Cross-Chapter Paper 7). The AR5 and SR1.5 indicated several specific climatic impact-driver changes that are particularly important to tropical forests: mean temperature increase, long-term drying trends (including shifts in the length of the dry season), prolonged drought, wildfires and surface CO <sub>2</sub> increase for inland forests ( [[#IPCC--2013|IPCC, 2013]] , 2018). The SRCCL assessed an enhanced risk and severity of wildfires in tropical rainforests ( ''high confidence'' ), but fires are not only a natural process but are also affected by deforestation and other human influences ( [[#IPCC--2019a|IPCC, 2019a]] ).

Temperature is rising in all tropical regions covered with forests and will ''very likely'' continue to rise, reaching levels unprecendented in recent decades as the temperature trends rapidly emerge from weak historical interannual variability (Sections 12.4.1–12.4.4 and 12.5.2; see also [[IPCC:Wg1:Chapter:Chapter-4|Chapter 4]] and Atlas).

Regional patterns of increasing drought or unusual wet and dry periods are predicted with agreement over many climate models such as over the Amazon basin ( [[#Boisier--2015|Boisier et al., 2015]] ; [[#Duffy--2015|Duffy et al., 2015]] ; [[#Zulkafli--2016|Zulkafli et al., 2016]] ; [[#Coppola--2021b|Coppola et al., 2021b]] ). There is ''medium confidence'' ( ''limited evidence'' , ''high agreement'' ) that in several tropical-forest regions (e.g., Amazonia, West Africa) the dry season length has increased ( [[#Fu--2013|Fu et al., 2013]] ; [[#Debortoli--2015|Debortoli et al., 2015]] ; [[#Saeed--2017|Saeed et al., 2017]] ; [[#Dunning--2018|Dunning et al., 2018]] ; [[#Wadsworth--2019|Wadsworth et al., 2019]] ), and there is ''low confidence'' ( ''limited evidence'' ) that deforestation influences the shift in the onset of the wet season in south Amazonia ( [[#Leite-Filho--2019|Leite-Filho et al., 2019]] ). In contrast, the wet season is increasing in northern Australia tropical forests ( [[#Catto--2012|Catto et al., 2012]] ).

Tropical forests typically reach peak fire weather conditions in the dry season ( [[#Taufik--2017|Taufik et al., 2017]] ), in particular during long-lived droughts ( [[#Brando--2014|Brando et al., 2014]] ; [[#Marengo--2018|Marengo et al., 2018]] ), with consequences for tree mortality, forest and carbon sink loss ( [[#Brando--2019|Brando et al., 2019]] ), and on the hydrological cycle in South America ( [[#Martinez--2014|Martinez and Dominguez, 2014]] ; [[#Espinoza--2020|Espinoza et al., 2020]] ). Observations and reanalyses over the past three to four decades, combined into fire risk indices, show that the fire weather season length has been increasing by about 20% globally ( [[#Jolly--2015|Jolly et al., 2015]] ), and this index exhibits particularly high trend values over tropical forest areas of South and Central America and Africa. There is generally ''low confidence'' in future projections of general fire weather risk evolution in tropical forests and evolutions depend on the region ( [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ). Over the Amazon basin the fire risk increase is projected to emerge well before 2050 while for other equatorial forests no significant evolution is found. In Savanna areas the risk increase is found to be more general.

'''In conclusion, most tropical forests are challenged by a mix of emerging warming trends that are particularly large in comparison to historical variability''' ( medium confidence '''). Water cycle changes bring prolonged drought, longer dry seasons, and increased fire weather to many tropical forests, with plants also responding to CO''' <sub>2</sub> '''increases''' ( medium confidence ''').'''

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