07 July 2007

Fire Alarm: Global Warming and Wildfires

Wildfire is seen approaching Old Faithful Village, Yellowstone National Park, in 1988. CREDIT: NPS PHOTO from http://www.sciencemag.org/content/vol313/issue5789/images/medium/927-2-med.gif

Fires Increase Due To Global Temperature Rise

While everybody talks about the threat posed by stronger hurricanes due to global warming (see this earlier post ), the greater danger in the American West is from increased number and severity of forest fires. (Fires are likely to increase in other regions as well: Australia, the Mediterranean basin, and so forth.)

The increase in temperature (0.9 degrees C over recent decades) is primarily responsible for the significant increase in wildfires in the West since the '80s.
Recent research shows that warmer temperatures appear to be increasing the duration and intensity of the wildfire season in the West. Since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999.

Research by Westerling et al. (2006) shows that the increase in western U.S. forest wildfires is correlated with warmer spring and summer temperatures, reduced precipitation associated with warmer temperatures, reduced snowpack and earlier spring snowmelts, and longer, drier summer fire seasons. Climate models indicate that these trends are part of plausible climate change scenarios (Running 2006), implying a further increase in the risk of large, damaging forest wildfires in parts of the western U.S.

These simulations unanimously project June to August temperature increases of 2° to 5°C by 2040 to 2069 for western North America. The simulations also project precipitation decreases of up to 15% for that time period. Even assuming the most optimistic result of no change in precipitation, a June to August temperature increase of 3°C would be roughly three times the spring-summer temperature increase that Westerling et al. have linked to the current trends. Wildfire burn areas in Canada are expected to increase by 74 to 118% in the next century, and similar increases seem likely for the western United States. (Running, 2006)
An analysis by Westerling & Bryant predicts significant increases in wildfire damage in Northern California forests as global warming continues. They conclude that this may make "wildfire a particularly important source of potential climate change impacts for the state." So though you might escape hurricanes or sea-level rise by moving to the foothills, you can't run from global warming.

[See update link to 2012 Climate Central report below.]

The Really Bad News

According to Running (2006), wildfires add an estimated 3.5 × 1015 g to atmospheric carbon emissions each year, or roughly 40% as much as fossil fuel carbon emissions. If climate change is increasing wildfire increases in this source of carbon emissions will accelerate the buildup of greenhouse gases and could provide a feed-forward acceleration of global warming.

In other words, the warmer it gets, the more and larger wildfires in western forests, releasing more CO2 to the atmosphere, resulting in more global warming, which might increase fire numbers, duration, and intensity even more.

In the long run the increase in wildfires in western montane forests will change the composition of plant communities, so that in time the Rockys of Colorado may look like the Sangre de Cristo Mountains of New Mexico look today.


Westerling et al., 2006. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. http://www.sciencemag.org/cgi/content/full/313/5789/940

Running, 2006. Is Global Warming Causing More, Larger Wildfires?

Westerling & Bryant, in prep. Climate Change and Wildfire in California. http://ulmo.ucmerced.edu/~westerling/pdffiles/07CC_WesterlingBryant.pdf

Update 2012-09-19:
Recent report confirms substantial increase in major fires, and predicts more in the future. Report here. Reuters article here.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

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Courtney said...

Fires in the WEST! Hmmm...I am 50 years old and that has been the story for the last 50+ years and many of the ecosystems in the Western US are based upon fire as part of that system.

This is extrapolation of the data on Global Warming is another Sky Scraper built on a cloud.

D. Wheat said...

The sources cited above show that there has been a substantial increase in fire numbers, intensity, and the length of the fire season in the last two decades. This is correlated with global warming rather than with land use or forestry practice changes. These are guys who study wildfires in detail for their whole careers. Take a look at the sources before you pooh-pooh the conclusions.