Wildfires are natural phenomena that occur when certain conditions are met, such as high temperatures, low humidity, dry fuels, and ignition sources. Wildfires can have both positive and negative effects on ecosystems and biodiversity, depending on the fire regime, the type of vegetation, and the fire management practices. However, wildfires also pose serious threats to human lives, health, property, and economy, especially in areas where human activities have altered the natural fire regime or increased the exposure and vulnerability of people and assets.

Climate change is a major factor that influences the occurrence and behavior of wildfires. Climate change can affect the frequency, intensity, duration, and seasonality of wildfires by altering the temperature, precipitation, wind, and lightning patterns. Climate change can also affect the availability and flammability of fuels by influencing the growth, mortality, and decomposition of plants and trees. Moreover, climate change can interact with other drivers of wildfires, such as land use, invasive species, pests and diseases, and fire suppression, to create more complex and dynamic fire scenarios.

According to the National Interagency Fire Center, the United States has experienced an average of approximately 70,000 wildfires per year since 1983, burning an average of 7 million acres per year. However, the number and size of wildfires have increased significantly in recent decades, especially in the western states. For example, in 2020, more than 10 million acres burned across the country, the highest annual total since 1983. The 2020 fire season also saw some of the largest and most destructive fires in history, such as the August Complex in California, which burned more than 1 million acres and became the first “gigafire” on record1.

Several studies have attributed the increase in wildfire activity in the United States to climate change, which has caused warmer and drier conditions, longer fire seasons, and more extreme fire weather. For instance, a study by Abatzoglou and Williams (2016) found that human-caused climate change accounted for 55% of the observed increase in fuel aridity (a measure of how dry and flammable the fuels are) from 1979 to 2015, and doubled the cumulative forest fire area since 19842. Another study by Westerling et al. (2006) found that the length of the fire season in the western United States increased by 78 days from 1970 to 2003, and the area burned by large fires (> 1000 acres) increased by 6.7 times, due to earlier snowmelt and higher spring and summer temperatures3.

Wildfires also have feedback effects on climate change, as they emit large amounts of greenhouse gases and aerosols that can affect the global and regional climate. Wildfires release carbon dioxide, methane, nitrous oxide, and other gases that contribute to the warming of the atmosphere. Wildfires also produce black carbon, organic carbon, and other particles that can affect the radiative balance of the Earth by scattering and absorbing solar radiation, and by influencing cloud formation and precipitation. The net effect of these emissions depends on the type, amount, and location of the fires, as well as the atmospheric conditions and the background concentrations of other pollutants.

The Intergovernmental Panel on Climate Change (IPCC) estimated that wildfires accounted for 5.5% of the total anthropogenic greenhouse gas emissions in 2010, and 8% of the total black carbon emissions in 20174. However, these estimates are uncertain and may not capture the full range of fire emissions, especially from peatlands, savannas, and agricultural fires. Moreover, these estimates do not consider the potential carbon sequestration by the regrowth of vegetation after fire, which can partially offset the emissions from combustion. The net carbon balance of wildfires is therefore highly variable and depends on the fire regime, the ecosystem type, and the recovery rate.

Wildfires also have significant impacts on human health, air quality, water resources, ecosystems, and biodiversity. Wildfires can cause direct injuries and fatalities, as well as respiratory and cardiovascular problems, due to the exposure to smoke and other hazardous substances. Wildfires can also degrade the air quality by increasing the levels of particulate matter, ozone, carbon monoxide, and other pollutants, which can affect the health of people living near or downwind of the fire. Wildfires can also affect the quantity and quality of water resources by altering the hydrological cycle, increasing the runoff and erosion, and contaminating the water supply with sediments, nutrients, metals, and organic compounds. Wildfires can also affect the structure, function,and diversity of ecosystems and biodiversity by changing the vegetation cover, soil properties, nutrient cycles, and fire regimes. Wildfires can also create opportunities for the invasion of non-native species, the spread of pests and diseases, and the loss of habitat and wildlife.

The impacts of wildfires on climate change and human and natural systems are expected to increase in the future, as climate change creates more favorable conditions for fire ignition and spread, and as human activities increase the exposure and vulnerability of people and assets to fire risk. Therefore, it is essential to enhance the understanding, monitoring, and prediction of wildfire behavior and effects, and to implement effective and adaptive strategies for fire prevention, preparedness, response, and recovery. It is also important to promote the sustainable and resilient management of forests and other ecosystems, and to reduce the greenhouse gas emissions that drive climate change and exacerbate fire risk.

In conclusion, wildfires are complex and dynamic phenomena that have multiple causes and consequences for climate change and human and natural systems. Wildfires are influenced by climate change, which can alter the temperature, precipitation, wind, and lightning patterns, and affect the availability and flammability of fuels. Wildfires also have feedback effects on climate change, as they emit greenhouse gases and aerosols that can affect the global and regional climate. Wildfires also have significant impacts on human health, air quality, water resources, ecosystems, and biodiversity, which can vary depending on the fire characteristics, the ecosystem type, and the exposure and vulnerability of people and assets. Wildfires pose serious challenges and risks for the present and future generations, and require coordinated and comprehensive actions to enhance the understanding, monitoring, and prediction of fire behavior and effects, and to implement effective and adaptive strategies for fire prevention, preparedness, response, and recovery. It is also essential to promote the sustainable and resilient management of forests and other ecosystems, and to reduce the greenhouse gas emissions that drive climate change and exacerbate fire risk.