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
