Global warming makes wildfires more likely and more destructive — an amplifying climate feedback that releases more carbon into the atmosphere. The full committee of the Senate for Energy and Natural Resources is having a hearing on the subject today. You can get live video here — click on Live Webcast.
I’m looking forward to this hearing since one of the witnesses is Dr. Thomas Swetnam, Director of the Laboratory of Tree Ring Research and Professor of Dendochronology, University of Arizona. He coathored the August 2006 Science cover story, “Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity” ($ub. req’d). The abstract is viewable online — here is the conclusion:
These results have important regional and global implications. Whether the changes observed in western hydroclimate and wildfire are the result of greenhouse gas-induced global warming or only an unusual natural fluctuation is beyond the scope of this work. Regardless of past trends, 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.
We are running out of time to stop these feedbacks from intensifying.