The company I work for is headquartered in Carlsbad, California, about 30 miles north of San Diego. Needless to say, the office has been closed for several days due to the terrible wildfires raging in southern California. CNN reports that nearly a million people have been evacuated, over a thousand homes have been destroyed, and Qualcomm stadium (home of the San Diego Chargers) has become a refugee center. Monetary damages could easily top one billion dollars.
Just last year Westerlin et al. 2006, Science, 313, 940-943, DOI:10.1126/science.1128834 reported the results of a study of wildfire activity in the western U.S. Here’s the abstract:
Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.
I’m fortunate to live in Maine (for many reasons!) so I wasn’t threatened by the wildfires. But I watched in horror as the fires threatened our headquarters, and couldn’t help but worry that some of my very good friends were in danger. I’ve spoken with a good friend in the area, only to find out that many of our staff have been evacuated, one of our IT professionals has suffered the loss of his home, as have the parents-in-law of one of my all-time best friends.
Westerlin et al. found a fourfold increase of major wildfires and a sixfold increase in the area of forest burned since 1986; this mirrors increases in wildfire activity in Canada (Gillett et al. 2004, Geophys. Res. Lett. 31, L18211). They make it quite clear that their study indicates it’s not just land-use changes, ecological factors, and fuels management that have led to what they call the “sudden” and “marked” increase in wildfire activity. In fact, they note the greatest increases in their data are in regions which are not greatly affected by these factors. They point to the culprit as increased spring and summer temperatures and an earlier spring snowmelt. And the cause for these is clear: global warming.
The best news from San Diego is undoubtedly the response of the people. Of people interviewed on the news, even those who have lost nearly everything — surely a devastating blow — still have only praise for the way the locals have responded, from ordinary citizens (including my good friend with whom I spoke) who have taken friends, neighbors, and strangers into their homes, to firefighters who have endured winds sometimes exceeding 100 mph and 40 hours or more of sleep deprivation, to military personnel who have answered every call with no muss, no fuss, just every bit of help they can provide. I’m well aware of the human capacity for apathy and cruelty. But I’m also aware of the human capacity for activity and kindness. The people of San Diego must be admired for showing us firsthand an example of the finest, an example to be emulated.
The impact of warmer summer temperature on wildfire threat is clear. But what’s not usually appreciated is that warmer temperatures in winter and spring affect the fire threat too, because they affect the timing of the melting of mountain snow and its associated runoff. This is clear in a number of studies, including a survey of rivers in New England (Hodgkins et al. 2003, Journal of Hydrology, 278, 244), and several studies of snowmelt runoff timing in the western U.S. (McCabe et al. 2005, Journal of Hydrometeorology, 6, 476; Regonda et al. 2005, Journal of Climate, 18, 372; Stewart et al. 2005, Journal of Climate, 18, 1136). Snowmelt runoff is a major source of water for both ecosystems and human society. Earlier arrival of snowmelt runoff leads to greater likelihood of drought in summer, and is a contributing cause to water shortages in California. As Westerlin et al. have shown, it’s also a contributing cause to wildfire activity.
Some think of the impact of global warming as being in the distant future, some view it as just around the corner, but the vast majority consider it something for the next generations. Yet those who keep a vigilant eye on the the planet’s fire and ice can see that global warming is right here right now. Global warming didn’t invent wildfires in the American west, they’ve been a threat all along. But considering that the American west has seen a fourfold increase of major wildfires and a sixfold increase in the area of forest burned already, one has to wonder what the future will bring if the climate science community is right, and the planet warms a further 2 to 3 deg.C this century — something which is unprecedented in all of human history.
In the meantime, my thoughts are with my friends in southern California.