Written by Max Michalec, ESLLC 2016-2017
Across the west there has been a dramatic trend over the last decade. Forest fires are burning longer and stronger than ever before. Last year the Forest Service spent over half of its annual budget fighting fires. The increase in fires can be attributed to climate change, with increased temperatures comes increased fuel aridity and more destructive fires. Climate change is not the only factor affecting the scope of recent fires. Fire suppression policies practiced by the government over the last hundred years have led to increasingly dense and fire prone forests. To determine how much the increase in fires is directly related to human caused climate change scientists from the University of Idaho and Columbia University have calculated how much of the increased scope and intensity of Western wildfires is caused by these affects. The study showed that since 1979, climate change is responsible for over half of the dryness of Western forests and the increased length of the fire season. Since 1984, these factors have enlarged the cumulative forest fire area of the United States by 16,000 square miles. That is about the size of Massachusetts and Connecticut combined.
Large fires (>300 acres) are responsible for over 95 percent of the area burned by wildfires in the United States in a given year according to the US Forest Service. These fires are frequently correlated with specific mesoscale (~5-1000 km) and broad scale (>1000 km) atmospheric circulation, temperature, and moisture patterns across regions of the U.S. The short-term weather conditions that are conducive to severe fires (i.e. fire weather) are manifestations of these patterns.
Climate warming associated with elevated levels of greenhouse-gas may create an atmospheric and fuel environment that is more conducive to large severe fires. The consensus view of the Intergovernmental Panel on Climate Change is that projected higher summer temperatures across the U.S. will likely increase the annual window of high fire risk by 10-30%. This may lead to an increase in area burned in Canada of 74-118% by the year 2100. General circulation model studies from USGS and other agencies suggest that fire occurrence or area burned could increase across North America under an increased CO2 environment because of increases in lightning activity, the frequency of surface pressure and associated circulation patterns conducive to surface drying, and fire-weather conditions in general that are conducive to severe wildfires.
Peterson, D.L.; Millar, C.I.; Joyce, L.A.; Furniss, M.J.; Halofsky, J.E.; Neilson, R.P.; Morelli, T.L. 2011. Responding to climate change in national forests: a guidebook for developing adaptation options. US Forest Service General Technical Report PNW-GTR-855, Pacific Northwest Research Station, Portland, OR.