The Associated Press reports on a recent paper in the journal Science that links wildfires in the Western US to global warming (notice the hedging in the AP article: Wildfires may be linked to global warming). According to the article:
Beginning about 1987, there was a change from infrequent fires averaging about one week in duration to more frequent ones that often burned five weeks or more, they reported. The length of the wildfire season was extended by 78 days.
The researchers said the changes appear to be linked to annual spring and summer temperatures, with many more wildfires burning in hotter years than in cooler years.
They also found a connection between early arrivals of the spring snowmelt in the mountainous regions and the incidence of large forest fires. An earlier snowmelt, they said, can lead to an earlier and longer dry season, which provides greater opportunities for large fires.
The paper is called Warming and Earlier Spring Increases Western U.S. Forest Wildfire Activity. In typical Science magazine style, it is quite readable, albeit brief so if you want further details you have to read other articles by the authors. The authors examined counter-explanations such land-use history (e.g., conversion of forests to grazing that would cause older trees to be cut down to be replaced by younger and skinnier trees called “fuels”) and cyclical changes in temperature (e.g., El-Nino). Their spatial models showed that climate change still was the culprit.
Note also, in the Science article, that climate change doesn’t just mean increasing temperatures but a whole host of interacting changes to the biosphere (FYI: numbers in parentheses below refer to citations in the bibliography):
climatic explanations posit that increasing variability in moisture conditions (wet/dry oscillations promoting biomass growth, then burning), and/or a trend of increasing drought frequency, and/or warming temperatures, have led to increased wildfire activity (13, 14).
…
On decadal scales, climatic means and variability shape the character of the vegetation (e.g., species populations and their drought tolerance (23), and biomass (fuel) continuity (24), thus also affecting fire regime responses to shorter term climate variability). On interannual and shorter time scales, climate variability affects the flammability of live and dead forest vegetation. (13–19, 25)
About the only quibble I have with the model is the assumptions in fitting different data sets together (technically, downscaling and interpolation) but that’s a problem you have with any large computer model, whether it models urban growth, national security risks, or climate change. (Also, they should have made use of a GIScientist because they would probably have seen even larger correlations if they looked at the data topologically.) Other than these issues, this is powerful evidence that climate change effects are being felt now.
(For those of you who’d like to point out that events, such as permafrost melting in Northern North America, are being felt now, let me amend the previous to be this is powerful evidence that climate change effects are being felt now in places where many people live.)
Update: Argh! CBC TV gets it wrong! CBC covered the article on the national news tonight. In the report, a university professor says that the article did not address the drivers of climate change. True, the authors do not address the issue of whether or not climate change is induced by humans. But then the reporter states that the authors don’t say whether the wildfires are due to cyclical weather patterns or from climate change. No. The article clearly rules out cyclical patterns. So much for our insightful reporters.