NASA satellites have been peering down at the Earth for more than 20 years, measuring ocean and atmospheric temperatures and tracking natural phenomena such as forest fires. In a new report by the Goddard Space Flight Center, NASA scientists say their analysis of all that data shows a strong link between higher global temperatures and the frequency and severity of forest fires.
“Our ability to track fires in a concerted way over the last 20 years with satellite data has captured large-scale trends, such as increased fire activity, consistent with a warming climate in places like the western U.S., Canada and other parts of Northern Hemisphere forests where fuels are abundant,” says Doug Morton, chief of the Biospheric Sciences Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Where warming and drying climate has increased the risk of fires, we’ve seen an increase in burning.”
The El Niño Southern Oscillation
One of the most accurate predictors of forest fires in North America is ocean temperatures in the Pacific ocean, a phenomenon known as the El Niño Southern Oscillation. Jim Randerson is an Earth system scientist at the University of California – Irvine who has studied fires both in the field and with satellite data in South America, Central America, parts of North America, Indonesia, Southeast Asia, and equatorial Asia.
“ENSO is a major driver of fire activity across multiple continents,” Randerson says. “The precipitation both before the fire season and during the fire season can be predicted using sea surface temperatures that are measured by NASA and NOAA satellites.”
High Temperatures & Low Humidity
The data shows that high temperatures and low humidity increase the likelihood of both natural fires from lightning strikes and fires caused by human activity. Hotter temperatures lead to more thunderstorms, which increase the likelihood of lighting.
“In the Western U.S., people are accidentally igniting fires all the time,” Randerson says. “But when we have a period of extreme weather, high temperatures, low humidity, then it’s more likely that typical outdoor activity might lead to an accidental fire that quickly gets out of control and becomes a large wildfire.” An example is the deadly Carr fire that struck California in 2018. The cause of that fire is believed to have been sparks from an aluminum alloy wheel as it dragged across the pavement after a blowout.
Higher Nighttime Temperatures
Higher average temperatures don’t just occur in the daytime when the sun is shining. Higher overnight temperatures also lead to a greater risk of fires. “Warmer nighttime temperature allow fires to burn through the night and burn more intensely, and that allows fires to spread over multiple days where previously, cooler nighttime temperatures might have weakened or extinguished the fire after only one day,” Doug Morton says.
Fire Feedback Effects
Fires add carbon dioxide to the atmosphere in a number of ways. First, they release the carbon stored in trees as they burn. Second, the trees destroyed by fires decompose over time, releasing more carbon. The smoke from fires contains particulates — the so-called black carbon that can embed in snow packs and hasten their melting. Those black particulates also absorb solar energy which adds to global warming. Those same particulates can travel thousands of miles downwind and contribute to respiratory and circulatory disease among humans and other animals.
Loss of vegetation from fires can contribute to destructive mudslides as well. Fires can also lead to melting of the permafrost, releasing large amounts of methane into the atmosphere, which further exacerbates global heating.
More Research Leads To Better Understanding
Fires of all types reshape the landscape and the atmosphere in ways that can resonate for decades. Understanding both their immediate and long term effects requires long term global data sets that follow fires from their detection to mapping the scale of their burned area, to tracing smoke through the atmosphere and monitoring changes to rainfall patterns.
“As climate warms, we have an increasing frequency of extreme events. It’s critical to monitor and understand extreme fires using satellite data so that we have the tools to successfully manage them in a warmer world,” Randerson says.
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