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The sun sets on the fire

Paul Wellman

The sun sets on the fire


Gap Fire: A Sign of Global Warming?

Climatologists Talk Causes of California’s Wildfire Onslaught


Parked on East Camino Cielo road last Thursday evening, near La Cumbre Peak, Santa Barbara surveyor Jacob Hecter watched stiff winds shoot spires of flame into the sky above the Goleta hills. Squinting into the sun, he asked a question with which many Californians can doubtless identify: does the fact that it’s early July and the state has already been besieged by 1,783 separate fires, including the Gap Fire and the massive Big Sur conflagration have something to do with climate change?

The answer is yes and no, say climate scientists. The current onslaught of wildfire “is what we’ve been projecting to happen, both in short-term fire forecasts and the longer term patterns that can be linked to global climate change,” said Ron Neilson, a professor at Oregon State University and bioclimatologist with the USDA Forest Service. Neilson, who for the last fifteen years has also worked for the UN’s Intergovernmental Panel on Climate Change (IPCC), cautioned that “with any single event you can’t say unequivocally that it’s climate change, or that it’s natural variability.” However, he said, “What I would tell people is that what they’re experiencing is very consistent with global warming.”

Wildfires in the western U.S. now occur more frequently, last longer, and cover more ground than they did in the past. A 2006 study published in Science found that since 1986, the number of major wildfires has increased by 400 percent, and the amount of land these fires burned increased by 600 percent, compared to the period from 1970 to 1986.

Until recently it was often assumed that spiking population growth and expanding land use patterns were mainly to blame for any increase in the number of big fires. But the Science study, which was conducted by researchers at the Scripps Institute and the UC Merced, concluded that these factors have had “relatively little effect.” Instead, the authors wrote, the change has come about mainly because summers have gotten longer, hotter, and drier. “The transition has been marked by a shift toward unusually warm springs, longer summer dry seasons, drier vegetation, and longer fire seasons.”

To date, the Science study is the most comprehensive look at past fire-patterns, but since its publication it has been buttressed by a steady stream of surveys and climate models indicating that global warming is making wildfires in the West more common and more severe. These projections tend to cite the same chief causes - hotter, drier weather lasting for longer periods. A new report conducted by the U.S. Climate Change Science Program - a federal agency directed by President Bush - and issued to Congress by the USDA, warns that arid areas (such as Santa Barbara) are “90-95 percent likely” to experience increases in fire risk in coming decades due to global warming. The report notes that over the course of the 20th century the global average temperature rose by 1 degree Fahrenheit. During the 21st, it’s projected to rise 3-10 degrees.

Not all of the connections between climate change and fire risk are immediately obvious. For example, climate models show that in coming decades rain will increasingly appear in the form of downpours, and the oscillation between wet and dry periods will lengthen. The implication this has for ecosystems - and their vulnerability to fire - is not good, because during prolonged periods of heavy rain, undergrowth is allowed to store up water and put on leafage. The problem, Neilson said, is that when that’s followed by a period of drought, the chances for a big fire are multiplied.

If you think about what happens to an ecosystem if it goes wet-dry-wet-dry for years, it just kind of putters along,” Neilson said. “It finds an equilibrium. But if you take exactly the same years and rearrange them so they go wet-wet-wet followed by dry-dry-dry, the ecosystem grows and puts on more and more leaf area. And then you start having dry years, and you have way more leaf area than can be supported by the available water. So the whole ecosystem dries out, and either it dies, gets attacked by insects, or gets hit by fire.” According to Neilson, Santa Barbara is less vulnerable to this phenomenon than other, more forested parts of the West; nevertheless, he said, it’s still a significant threat.

Another unfortunate aspect of the interaction between climate change and wildfires is the fact that the latter are responsible for a huge proportion of annual carbon emissions - up to forty percent in the U.S.- and this, in turn, fuels the former. As a recent article in New Scientist put it, “If climate change is increasing wildfire, these new sources of carbon emissions will accelerate the buildup of greenhouse gases and could provide a feed-forward acceleration of global warming.”

This year’s fire forecast - it can be accessed on the U.S. Forest Service website - is one of the worst in recent memory. California is expected to be especially hard hit. “This is one of the most intense fire periods we’ve forecast in the last half a dozen years,” Neilson said, “and the interesting thing is that we don’t even forecast lightening, which touched off most of the California fires.”

In a sense it doesn’t seem to matter how closely conflagrations like the Gap Fire can be linked to climate change. What is relevant is that big wildfires are more likely because there’s less rain and snowmelt than there used to be, and hotter average temperatures, and both of these developments will worsen as global warming intensifies. That seems to be the take home message most climate scientists are trying to impart, and they appear to have a receptive audience in the public. As he surveyed the blaze from his perch near La Cumbre Peak Thursday evening, Hecter was philosophical about its possible connection to climate change. “Whether that’s global warming or not, it’s ugly,” he said. “And it’s only July.”

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