Key messages
- We are entering a new age of intensifying extreme fire regimes (megafires). It is likely that these are induced, and certainly exacerbated by, anthropogenic climate change.
- Several megafires have been observed across very diverse regions from high to low latitudes, and are now impacting ecosystems that typically do not have a history of wildfires.
- Megafires can affect entire biomes with unprecedented impacts on flora and fauna, threatening also more fire-sensitive ecosystems such as the World Heritage-listed Gondwana rainforests of Australia.
- Large greenhouse gas emissions released by megafires enhance positive fire-climate feedback, which sustain and worsen conditions that increase the likelihood of even more devastating wildfires.
- Large smoke plumes and aerosols from megafires can impact wide areas due to long-range transport both in the troposphere and stratosphere.
- Worsening fire regimes (more frequent fires, more intense fires) come with increased risks to respiratory and cardiovascular health, birth outcomes and mental health for rural and urban communities.
Insight explained
New scientific advances confirm previous warnings that human-induced climate change is intensifying fire regimes. There have been increases in fire extent, intensity and the duration of the fire season, as well as a change in the available fuels, resulting in an increased frequency and intensity of fires. Megafires, high-intensity wildfires that spread uncontrolled over large areas, reaching extreme fire intensities, are likely to be increasingly frequent. Megafires cause greenhouse gas and aerosol emissions, which are unprecedented for the affected biome, and impact air quality on local and continental scales.
Researchers have recently been able to attribute fire and megafire events more clearly to human interference – such as the 2021 wildfires in western North America that were preconditioned by an extreme heatwave. Evidence for human influence is found in fire seasons of unprecedented magnitude in the modern era in regions and countries as diverse as California, Australia, the Mediterranean basin, Canada and the Arctic. It is now possible, with at least medium confidence, to attribute human influence on weather events, namely extreme drought, heat, lightning activities and often high winds, that increase the fire risk. The IPCC Working Group I Sixth Assessment Report (IPCC AR6 (WGI)) projects future increases of fire weather with medium or high confidence on every inhabited continent, primarily due to higher temperatures and reduced precipitation.7 There is medium confidence that there is a positive carbon-climate feedback loop with fires releasing greenhouse gases enhancing the drier and fire-prone conditions that favour fires.8
Recent fires have caused significant impacts on human health. Wildfire smoke is known to affect respiratory health, and there is growing evidence of impacts on cardiovascular health, mortality, birth outcomes and mental health. Smoke from wildfires also affects local and distant air quality. The 2019–2020 Australian wildfires affected New Zealand and South America, and smoke from Siberian fires has affected North America. Current assessments estimate over 677,000 deaths per year globally from landscape fires with the largest contribution from the Arctic, South-east Asia, central and west Africa and the Amazon.9
As climate changes, the occurrence of megafires is not constrained to fire-prone ecosystems alone. A change in tropical forests’ moisture, for instance, may promote much larger fires. Changing fire regimes will have important consequences for the world’s biodiversity, regional human health and the global climate system.
Highlights
- 9,000 –plant species (more than one-third of all Australian species), 832 vertebrate fauna species, including 21 threatened species were affected across the 2019/20 fire grounds in Australia.
- 0.67 gigatons of carbon stocks – net loss of biomass in the Amazon from 2010-2019 largely due to fires contributing to the conversion of the Amazon from a carbon sink into a source.
- 35% – more CO2 released from Arctic wildfires in the first 8 months of 2020 compared to the entire previous year (2019).
Background
Wildfires are an intrinsic feature of many ecosystems around the world, and are a prerequisite for many plant species to reproduce. Many factors affect whether a wildfire starts and how severe it is, such as weather, vegetation structure (fuel availability), terrain (or topography), land and fire management practices and human presence that may – on purpose or by accident – ignite a fire. Wildfires occur in some ecosystems, such as Australian savannahs, almost annually; in Australian temperate forests they occur multiple times in a decade (potentially increasing in frequency now), and in ecosystems such as undisturbed rainforests wildfires only rarely occur, usually on centennial scales, such as in boreal forests in North America and in Siberia (100-300 years between events). In Siberian boreal forests normal fire conditions burn only the forest floor, leaving standing trees alive. Extreme drought conditions that burn entire forest stands (crown fires – burning even forest canopies) used to occur only every 10 to 15 years and affected 3 to 10 million hectares in Siberia. Climate change is impacting the frequency and severity of fires, causing extreme fire years to become more extreme.
Implications & Recommendations
At a global level, decision makers need to:
- limit global warming with all measures possible to decrease the risk of more frequent and intense megafires.
At a regional level, governments need to:
- revise and adapt fire management planning to account for a diverse range of affected ecosystems, which requires land management methods that are region- and context-specific.
At national and local levels, policy makers need to:
- include megafires and their impact on greenhouse gas emissions in the budgets for the 1.5°C-target;
- implement monitoring and forecasting systems of weather conditions and wildfires, which may support adaptation to the devastating effects of these fires;
- provide protection measures by controlling and penalizing illegal deforestation where fire is used as a land-clearing technique;
- adapt forest management methods such as forest fuel treatments, the intentional reduction of material that burns in fire-prone forest areas, to local biomes and climatic conditions;
- consider collaborating with indigenous communities to re-engage with traditional land management practices, such as cultural burning;
- increase the resilience of communities in affected areas (taking account of an increased fire risk when planning, building and improving infrastructure);
- consider techniques to reduce exposure to particulate matter from wildfire such as the use of air cleaners in indoor spaces, thereby protecting people’s health;
- increase monitoring of air pollution, including with low-cost sensors, and the development of better forecasting to warn people about air pollution levels.
Megafires can enhance emissions of methane
Intensifying fire regimes have devastating effects on ecosystems. The increased occurrence of fires as well as their growing intensity threatens biodiversity and can lead to an increase in emissions of greenhouse gases including methane. An increase in fire activity in both 2019 and 2020 associated with deforestation in the Amazon region significantly increased emissions of methane, with direct emissions of methane of 0.5 to 7.0 megatonnes of CH4 per year-1 (depending on the severity of the burn season), not including additional indirect emissions due to ecosystem degradation.10 The unprecedented Arctic wildfires in 2019 and 2020 represent another significant source of methane, both directly from burning, but also indirectly from accelerated permafrost thaw.11 In both regions, direct and indirect emissions of greenhouse gases now largely exceed carbon uptake by regrowth of vegetation. Although the carbon-climate feedback of accelerating fire activity and emission of greenhouse gases is expected to increase strongly, this is currently underrepresented both in coupled climate models as well as in international considerations when estimating global greenhouse gas budgets to stay within the 1.5°C target.
Australia
After record heat and drought, Australia experienced abnormally severe fires of unprecedented extent, including the largest single-ignition fire on record, which was greater than 500,000 hectares, in the season of 2019-2020. An estimated 715 (range 517-867) Mt gross CO2 in total were emitted from these fires. Furthermore, these megafires affected entire biomes in southern and eastern Australia with unprecedented impacts on flora and fauna. The fires not only affected savannahs and eucalypt forests that are well adapted to wildfire, but also more fire-sensitive ecosystems, threatening the World Heritage-listed Gondwana rainforests.
The Arctic and Siberia
In the Arctic Circle and Siberia, a rise in arctic temperatures and dry lightning caused large areas to burn. In 2019 about 10 million hectares – more than the size of Portugal – burned in Siberia and the Russian Arctic. This was followed by another extreme fire year in 2020 when nearly 14 million hectares burned in the region. Extreme fires occurred again in 2021. Altogether, the fires in the Arctic and Siberia released about 175 Mt of gross CO2 in 2019 and nearly 250 Mt of gross CO2 in 2020.
Brazil
In the world’s largest wetland, the Brazilian Pantanal, there was a 245% increase in burned areas in 2020 compared to the previous 10 years. Reasons for this are extreme drying (due to 50% less rain than in the previous year) and intensified anthropogenic burning for intentional legal and illegal deforestation to reform pastures or make room for agriculture.12 It led to emissions of 115 Mt of gross CO2 and 524 tonnes of harmful fine particulate matter (PM2.5). Populations of many animal and plant species were affected, many of which are rare or endemic. There is growing concern that the fragile ecosystem of the Pantanal area may never recover.
USA
Since 2018, the US south-west has experienced some of the worst fires ever seen in the region. Californian megafires burned over months and became the 7 largest wildfires ever recorded until 2020. The largest megafire, the August complex fire, burned more than 400,000 hectares of different forest and shrubland types. Such high fire severity over an extremely large area puts the recovery of plants and animals, most of them rare or endemic, under threat. Smoke released by these fires reached critical levels for human health along the US west coast, with San Francisco covered under an orange sky for days. The smoke travelled across the northern hemisphere and aerosol particles from the fires were measured as far away as Germany. The 2020 California and Oregon wildfires led to excess carbon emissions of at least 30 Mt of gross CO2 in a single year.
