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Joseph Romm

Joseph Romm

Posted: October 24, 2007 12:09 PM

Global Warming and the California Wildfires


ca-wildfires.jpg



Global warming makes wildfires more likely and more destructive -- as many scientific studies have concluded. Why? Global warming leads to more intense droughts, hotter weather, earlier snowmelt (hence less humid late summers and early autumns), and more tree infestations (like the pine beetle). That means wildfires are a dangerous amplifying feedback, whereby global warming causes more wildfires, which release carbon dioxide, thereby accelerating global warming.

The climate-wildfire link should be a special concern in this country where, since 2000, wildfires have burned an area larger than the state of Idaho.

I write this as my San Diego relatives wait anxiously in their hotel room to find out if their Rancho Santa Fe home has been destroyed. This is a beautiful home that I lived in for a month when I moved to the area in the mid-1980s to study at the Scripps Institution of Oceanography.

Can we say that the brutal San Diego wildfires were directly caused by global warming? Princeton's Michael Oppenheimer put it this way on NBC Nightly News Tuesday:

The weather we've seen this fall may or may not be due to the global warming trend, but it's certainly a clear picture of what the future is going to look like if we don't act quickly to cut emissions of the greenhouse gases.

Thomas Swetnam, University of Arizona climate scientist, who coauthored a major study on the subject (see below) said in 2006:

We're showing warming and earlier springs tying in with large forest fire frequencies. Lots of people think climate change and the ecological responses are 50 to 100 years away. But it's not 50 to 100 years away--it's happening now in forest ecosystems through fire.

I researched wildfires for my book -- hence the "Hell" in Hell and High Water -- and my view is closer to Swetnam's for several reasons.

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First, Southern California is experiencing the "driest year in 130 years of recordkeeping," precisely the kind of extreme weather event we expect from climate change. We are seeing record droughts around the country -- and around the world. Some scientists fear we are at risk of shifting the climate to "a permanent drought by 2050 throughout the Southwest."

Second, we aren't just seeing bad wildfires, we are seeing record-shattering wildfires. The 2005 wildfire season, which ravaged 8.7 million acres, was record-breaking, and the record it broke was from 2000, when wildfires consumed 8.4 million acres. The 2006 wildfire season easily surpassed 2005, with a stunning 9.9 million acres burned. The 2007 wildfire season is also on a pace to beat 2005.

The August 2006 Science cover story, "Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity" (subs. req'd) that Swetnam coathored with three Scripps researchers explicitly examined and then rejected the theory that land-use and fire-supression practices were the cause of the surge in wildfires since the mid-1980s.

Some global warming deniers may cross their fingers and call it all a coincidence and criticize the (few) journalists that even raise the wildfire-climate connection. But in fact, a major 2004 study warned that things will get much, much worse if we don't take action soon to reverse greenhouse gas emissions trends. Researchers at the U.S. Forest Services Pacific Wildland Fire Lab looked at past fires in the West to create a statistical model of how future climate change may affect wildfires. Their work suggests that "the area burned by wildfires in 11 Western states could double ... if summer climate warms by slightly more than a degree and a half" centigrade. On our current emissions path, this is likely to happen by mid-century. By century's end, states like Montana, New Mexico, Washington, Utah, and Wyoming could see burn areas increase five times.

The third reason to worry about the climate-wildfire connection is that wildfires are a classic amplifying feedback, since burning forests release carbon dioxide that accelerates global warming. As the 2006 Science article concludes soberly:

... virtually all climate-model projections indicate that warmer springs and summers will occur over the region in coming decades. These trends will reinforce the tendency toward early spring snowmelt and longer fire seasons. This will accentuate conditions favorable to the occurrence of large wildfires, amplifying the vulnerability the region has experienced since the mid-1980s. The Intergovernmental Panel on Climate Change's consensus range of 1.5° to 5.8°C projected global surface temperature warming by the end of the 21st century is considerably larger than the recent warming of less than 0.9°C observed in spring and summer during recent decades over the western region.

If the average length and intensity of summer drought increases in the Northern Rockies and mountains elsewhere in the western United States, an increased frequency of large wildfires will lead to changes in forest composition and reduced tree densities, thus affecting carbon pools. Current estimates indicate that western U.S. forests are responsible for 20 to 40% of total U.S. carbon sequestration. If wildfire trends continue, at least initially, this biomass burning will result in carbon release, suggesting that the forests of the western United States may become a source of increased atmospheric carbon dioxide rather than a sink, even under a relatively modest temperature-increase scenario. Moreover, a recent study has shown that warmer, longer growing seasons lead to reduced CO2 uptake in high-elevation forests, particularly during droughts. Hence, the projected regional warming and consequent increase in wildfire activity in the western United States is likely to magnify the threats to human communities and ecosystems, and substantially increase the management challenges in restoring forests and reducing greenhouse gas emissions.

My thoughts are with my San Diego relatives and the stunning half-million evacuees -- a Katrina-like exodus. We are simply running out of time to stop all of the carbon cycle feedbacks from intensifying and to stop these devastating, record-breaking wildfires from becoming the normal climate.

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