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
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
Thomas Swetnam, University of Arizona climate scientist, who coauthored a
major study on the subject (see below) said in 2006:
I researched wildfires for my book -- hence the "Hell" in Hell
and High Water -- and my view is closer to Swetnam's for several
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
permanent drought by 2050 throughout the Southwest."
Second, we aren't just seeing bad wildfires, we are seeing record-shattering
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.
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
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.