Climate change is making wildfires worse, increasing both their number and severity. For as bad as the fire seasons in recent years might seem, things are actually projected to get much worse as global average temperatures continue to climb, roughly doubling in scope the problems we’re seeing today.
How climate change causes an increase in wildfires
There are a number of variables related to climate change that make severe wildfires more likely. Any one of these factors alone can contribute to the problem, but collectively they amount to a perfect storm.
The most obvious is heat: warmer temperatures mean hotter air and parched vegetation, creating the conditions ideal for wildfires. “The warmer atmosphere sucks more moisture from plants and soil,” writes Craig Welch. “To cut their losses during droughts, trees close their pores in their leaves, called stomata, or shed leaves entirely. But that limits the CO2 they take in, leaving them both hungry and parched all at once. When it’s especially hot, they even leak some of the water they’re desperate to retain.” (Welch, 2022, p. 56)
Summers are not only hotter, but warmer temperatures are starting earlier in the season and lasting longer. “As winter wanes and leaves start to peek out from branches, trees draw more water from the soil and move it into the sky–a process called evapotranspiration,” writes Jonathan Lambert. When this process begins earlier in the season, as has been happening due to climate change, it leaves soils dryer in the summer throughout much of the Northern hemisphere, contributing to dry spells and leaving vegetation parched. (Lambert, 2020) A seemingly minor change like starting this process a week sooner and extending the warm weather a week later into the season can have a dramatic effect. With each passing year, vegetation falls a little further behind on this water balance, making it a lot more vulnerable.
Warmer temperatures also allow clouds to hold more water vapor, which results in uneven rainfall. Certain areas get drenched with a lot of rain that falls in a short period of time and then runs off, while other areas are starved of precipitation. So you end up experiencing opposing problems simultaneously: drought over large areas and flooding problems in others. These conditions can also result in more dry lightning: fire-igniting bolts that strike the ground in the absence of any rain.
Shifting temperatures are also disrupting the balance of forest ecosystems, resulting in unhealthy forests. For example, the bark beetle invasion that’s been killing trees in bulk shifts farther north as average annual temperatures rise in the Northern latitude. Which means more forests filled with dead trees, creating the fuel for massive wildfires. Invasive species such as cheatgrass can add kindling for fires.
Determining climate change’s role in wildfires
Calculating the effect climate change has on wildfires is complicated, because forest fires are affected not just by heat, drought and levels of precipitation but also by wind, humidity, and other factors. That said, there’s no doubt it is playing a role.
For example, a study of the 2019 wildfires in Australia found that climate change increased the risk by at least 30%. “We think it is much larger than that,” says lead author Geerk Jan Van Oldenborgh, “but we can’t prove that until we find out why there is this discrepancy between the observations and the climate models.”
It’s estimated extreme fires are around 4-times more likely than they were prior to 1900. (Fountain, 3-5-2020) A large chunk of this increase is due to global warming. Climate change is likely to make extreme blazes like Australia’s 2019 wildfire season 3-times as common, increasing from once every 17 years to once every 6 years. (Gramling, 2020)
Unfortunately, wildfires are one of those self-reciprocating cycles in climate change. Burning forests release more carbon into the atmosphere. A 2021 study found global carbon emissions from forest fires increased 60% since 2001. Fires in Canada alone now produce more emissions than every country except the U.S., China an India. (The Week, 11-8-2024, p. 21) The 2019 Australian wildfires created the loftiest and largest cloud of smoke ever measured, sending plumes of aerosols into the atmosphere that are on par with the strongest volcanic eruptions in the past 25 years. (Science News, 1-16-2021, p. 4)
Wildfires also burn the trees that normally soak up carbon. So in a vicious cycle, the more wildfires there are, the more it fuels climate change, which leads to even more severe wildfires.
“We’re using terms like ‘mega’ and ‘giga’ to describe wildfires,” says University of Tasmania epidemiologist Fay Johnston, a leading wildfire smoke researcher, “but it’s really just the beginning. If we don’t do anything about climate change, we ain’t seen nothing yet.” (Gorney, 2021)
References:
- Fountain, H. (2020, March 5) “Warming contributed to wildfires, study finds,” New York Times, A6
- Gorney, C. (2021) “Where there’s fire, there’s toxic smoke,” National Geographic, April, pp., 60-77
- Gramling, C. (2020, March 28) “Australian fires tied to climate change,” Science News, 197(6):6
- Lambert, J. (2020) “Early spring dries summer soils,” Science News, Feb. 1, 197(2):14
- Welch, C. (2022) “Heat and drought are killing forests. But we can limit the damage if we change course now.” National Geographic, May, pp. 34-73