Editing IPCC:AR6/WGII/Chapter-2 (section)

==== 2.5.3.2 Risks to Ecosystems and Services from Wildfire ====

<div id="h3-44-siblings" class="h3-siblings"></div>

<div id="2.5.3.2.1" class="h4-container"></div>

<span id="future-projections-of-wildfire-globally"></span>
===== 2.5.3.2.1 Future projections of wildfire globally =====

<div id="h4-37-siblings" class="h4-siblings"></div>

Continued climate change under high-emission scenarios that increase global temperature ~4°C by 2100 could increase global burned area by 50% ( [[#Knorr--2016b|Knorr et al., 2016b]] ) to 70% ( [[#Kloster--2017|Kloster and Lasslop, 2017]] ) and global mean fire frequency by ~30% ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ), with increases on one-third ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ) to two-thirds ( [[#Moritz--2012|Moritz et al., 2012]] ) and decreases on one-fifth ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Moritz--2012|Moritz et al., 2012]] ) of land globally. Lower emissions that would limit the global temperature increase to &lt;2°C would reduce projected increases of global burned area to 30% ( [[#Lange--2020|Lange et al., 2020]] ) to 35% ( [[#Kloster--2017|Kloster and Lasslop, 2017]] ) and projected increases of fire frequency to ~20% ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Huang--2015|Huang et al., 2015]] ). Continued climate change could further lengthen fire weather seasons ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Models combining projected climate change with potential agricultural expansion project decreases in total burned area ( [[#Huang--2015|Huang et al., 2015]] ; [[#Knorr--2016b|Knorr et al., 2016b]] ; [[#Park--2021|Park et al., 2021]] ). The area of projected increases in burned area and fire frequency due solely to continued climate change is higher for the world as a whole than the area of projected decreases ( ''medium evidence'' , ''medium agreement'' ).

Increased wildfire due to continued climate change increases risks of tree mortality (Sections 2.5.2.6, 2.5.2.7, 2.5.3.2), biome shifts ( [[#2.5.2.2|Section 2.5.2.2]] ) and carbon emissions (Sections 2.5.2.10, 2.5.3.4). Wildfire and biome shifts under a projected climate change of 4°C above the pre-industrial period, combined with international trade and transport, cause high risks from invasive species across one-sixth of the global area including extensive high-biodiversity regions ( [[#Early--2016|Early et al., 2016]] ).

Wildfire risks to people include death and destruction of their homes, respiratory illnesses from smoke ( [[#Ford--2018|Ford et al., 2018]] ; [[#Machado-Silva--2020|Machado-Silva et al., 2020]] ), post-fire flooding from areas exposed by vegetation loss and degraded water quality due to increased sediment flow ( [[#Dahm--2015|Dahm et al., 2015]] ) and the chemical precursors of carcinogenic trihalomethanes when water is later chlorinated for drinking ( [[#2.5.3|Section 2.5.3.7]] ) ( [[#Uzun--2020|Uzun et al., 2020]] ). Under RCP8.5 and shared socioeconomic pathway SSP3 (high population growth, slow urbanisation), the number of people living in fire-prone areas could increase by three-quarters to 720 million in 2100, in a projected global population of 12.4 billion people ( [[#Knorr--2016b|Knorr et al., 2016b]] ). Lower emissions under RCP4.5 could reduce the number of people at risk by 70 million. In these projections, human population growth increases human exposure to wildfires more than increases in burned area ( [[#Knorr--2016b|Knorr et al., 2016b]] ). A global temperature increase &lt;2°C could increase global population exposure to wildfire by ~30% ( [[#Lange--2020|Lange et al., 2020]] ). Increased wildfire under continued climate change increases the probability of human exposure to fire and risks to public health ( ''medium evidence'' , ''high agreement'' ).

<div id="2.5.3.2.2" class="h4-container"></div>

<span id="future-projections-of-wildfire-in-high-risk-areas"></span>
===== 2.5.3.2.2 Future projections of wildfire in high-risk areas =====

<div id="h4-38-siblings" class="h4-siblings"></div>

Regions identified by multiple global analyses as being at a high risk of increased burned area, fire frequency and fire weather include: the Amazon ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Huang--2015|Huang et al., 2015]] ; [[#Knorr--2016b|Knorr et al., 2016b]] ; [[#Burton--2018|Burton et al., 2018]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ), Mediterranean Europe ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Burton--2018|Burton et al., 2018]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ), the Arctic tundra ( [[#Moritz--2012|Moritz et al., 2012]] ; [[#Flannigan--2013|Flannigan et al., 2013]] ), Western Australia ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Burton--2018|Burton et al., 2018]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ) and the western USA ( [[#Gonzalez--2010|Gonzalez et al., 2010]] ; [[#Moritz--2012|Moritz et al., 2012]] ; [[#Knorr--2016b|Knorr et al., 2016b]] ). Higher-resolution spatial projections indicate high risks of increased wildfire in the Amazon, Australia, boreal ecosystems, Mediterranean Europe and the USA with climate change ( ''medium evidence'' , ''medium agreement'' ).

In the Amazon, climate change under RCP8.5, combined with high deforestation, could double the area of high fire probability ( [[#Fonseca--2019|Fonseca et al., 2019]] ), double the burned area by 2050 ( [[#Brando--2020|Brando et al., 2020]] ), increase the burned area by 400–2800% by 2100 ( [[#Le%20Page--2017|Le Page et al., 2017]] ) and increase fire intensity by 90% ( [[#De%20Faria--2017|De Faria et al., 2017]] ). Lower GHG emissions (RCP4.5) and reduced deforestation could reduce the risk of fires to a one-fifth increase in the area of high fire probability ( [[#Fonseca--2019|Fonseca et al., 2019]] ) and a 100–500% increase in burned area by 2100 ( [[#Le%20Page--2017|Le Page et al., 2017]] ). Moreover, increased fire, deforestation and drought, acting via vegetation–atmosphere feedbacks, increase the risk of extensive forest dieback and potential biome shifts of up to half of the Amazon rainforest to grassland, a tipping point that could release an amount of carbon that would substantially increase global emissions ( [[#Oyama--2003|Oyama and Nobre, 2003]] ; [[#Sampaio--2007|Sampaio et al., 2007]] ; [[#Lenton--2008|Lenton et al., 2008]] ; [[#Nepstad--2008|Nepstad et al., 2008]] ; [[#Malhi--2009|Malhi et al., 2009]] ; [[#Settele--2014|Settele et al., 2014]] ; [[#Lyra--2016|Lyra et al., 2016]] ; [[#Zemp--2017a|Zemp et al., 2017a]] ; [[#Zemp--2017b|Zemp et al., 2017b]] ; [[#Brando--2020|Brando et al., 2020]] ). Continued climate change, combined with deforestation, increases risks of wildfire and extensive forest dieback in the Amazon rainforest ( ''robust evidence'' , ''high agreement'' ).

In Australia, climate change under RCP8.5 increases the risk of pyro-convective fire by 20–40 days in rangelands of Western Australia, South Australia and the Northern Territory ( [[#Dowdy--2019|Dowdy et al., 2019]] ). Pyro-convective fire conditions could reach more frequently into the more populated areas of New South Wales, particularly at the start of the austral summer ( [[#Di%20Virgilio--2019|Di Virgilio et al., 2019]] ). GCMs do not agree, however, on the areas of projected fire increase in New South Wales ( [[#Clarke--2019|Clarke and Evans, 2019]] ). Increases in heat and potential increases in wildfire threaten the existence of temperature montane rainforest in Tasmania, Australia ( [[#Mariani--2019|Mariani et al., 2019]] ).

In Mediterranean Europe, climate change of 3°C of warming could double or triple the burned area whereas keeping the temperature increase to 1.5°C could limit the increase in burned area to 40–50% ( [[#Turco--2018|Turco et al., 2018]] ). Under RCP8.5, the frequency of heat-induced fire weather could increase by 30% ( [[#Ruffault--2020|Ruffault et al., 2020]] ). Severe fire followed by drought could cause biome shifts of forest to non-forest ( [[#Batllori--2019|Batllori et al., 2019]] ) and tree mortality &gt;50% ( [[#Dupire--2019|Dupire et al., 2019]] ).

In the Arctic tundra, boreal forests and northern peatlands, including permafrost areas, climate change under the scenario of a 4°C temperature increase could triple the burned area in Canada ( [[#Boulanger--2014|Boulanger et al., 2014]] ), double the number of fires in Finland ( [[#Lehtonen--2016|Lehtonen et al., 2016]] ), increase the lightning-driven burned area by 30–250% ( [[#Veraverbeke--2017|Veraverbeke et al., 2017]] ; [[#Chen--2021a|Chen et al., 2021a]] ), push half of the area of tundra and boreal forest in Alaska above the burning threshold temperature and double the burned area in Alaska ( [[#Young--2017a|Young et al., 2017a]] ). Thawing of Arctic permafrost due to a projected temperature of 4°C and the resultant wildfires could release 11–200 GtC which could substantially exacerbate climate change ( [[#2.5.2.9|Section 2.5.2.9]] ).

In the USA, climate change under RCP8.5 could increase the burned area by 60–80% by 2049 ( [[#Buotte--2019|Buotte et al., 2019]] ) and the number of fires with an area &gt;50 km 2 by 300–400% by 2070 ( [[#Barbero--2015|Barbero et al., 2015]] ). In montane forests, climate change under RCP8.5 increases the risk of fire-facilitated conversion of ~7% of forest to non-forest by 2050 ( [[#Parks--2019|Parks et al., 2019]] ). In California, climate change under a scenario of a 4°C temperature increase could double fire frequency in some areas ( [[#Mann--2016|Mann et al., 2016]] ), but emission reductions that limit the temperature increase to ~2°C could keep this from increasing ( [[#Westerling--2011|Westerling et al., 2011]] ). Carbon dioxide fertilisation and increased temperature under climate change could increase invasive grasses and wildfire in desert ecosystems of the southwestern USA where wildfire has historically been absent or infrequent, and increase the mortality of the sparse tree cover (Horn and St. Clair, 2017; [[#Klinger--2017|Klinger and Brooks, 2017]] ; [[#Syphard--2017|Syphard et al., 2017]] ; [[#Moloney--2019|Moloney et al., 2019]] ; [[#Sweet--2019|Sweet et al., 2019]] ).

In summary, under a high-emission scenario that increases global temperature 4°C by 2100, climate change could increase the global burned area by 50–70% and the global mean fire frequency by ~30%, with increases on one- to two-thirds and decreases on one-fifth of global land ( ''medium confidence'' ). Lower emissions that would limit the global temperature increase to &lt;2°C would reduce projected increases of burned area to ~35% and projected increases of fire frequency to ~20% ( ''medium confidence'' ). Increased wildfire, combined with erosion due to deforestation, could degrade water supplies ( ''high confidence'' ). For ecosystems with an historically low fire frequency, a projected 4°C rise in global temperature increases risks of fire, contributing to potential tree mortality and conversion of over half the Amazon rainforest to grassland and thawing of the Arctic permafrost that could release 11–200 GtC that could substantially exacerbate climate change ( ''medium confidence'' ).

<div id="2.5.3.3" class="h3-container"></div>

<span id="risks-to-ecosystems-and-services-from-tree-mortality"></span>