In case you’ve been living under a log, forest fires have been a serious problem lately. So far this year just over 6 million acres have burned nationwide, almost double the ten-year year-to-date average. Out of the 25 currently reported large fires in the US, 17 are burning in the Pacific Northwest, totaling 65,391 acres. The story north of the border has been even more dire. And forests fires aren’t just frightening, they’re expensive. From 1999-2003 the U.S. government alone spent an average of $1.3 billion dollars per year fighting the nation’s wildfires.

Not surprisingly, the U.S. Forest Service has taken a lot of, shall we say, heat recently for its fire fighting policies. Over the long term, suppressing forest fires in the West has allowed undergrowth and other combustible fuels to build up—which leads to bigger conflagrations once fire does break out.

However, a new study by scientists at the University of Washington shows that it is climate, not fuel buildup, that has the dominant influence on the extent and severity of forest fires.

Over the past century, fires have been more frequent and more severe during hotter, drier summers, even during low fuel years, and less frequent and severe during cooler summers with high amounts of ground fuel.

All available climate models predict warmer and drier summers for the Northwest over the next century, with regional temperatures expected to rise .4-.9 degrees fahrenheit per decade in this century (100-200% the rate of increase during the last quarter of the 20th century). As the climate warms, fire seasons will gradually start earlier and end later, and new areas completely unused to the threat of fire will begin to go up in smoke. This is already happening in Washington, where the fire season started 3 months early this year. Furthermore, these climate changes not only cause fires, but also wipe out forest stands by reducing trees’ resistance to diseases and to insects such as the Mountain Pine Beetle. The Climate Impact Group warns that as the region continues to warm, forest coverage in the Cascades could decrease by 20-50%.

So, while forest management practices have certainly contributed to the forest fire problem, the time may have finally arrived when greenhouse gases will replace the chainsaw as the leading threat to the health of Cascadia’s forests.

9/1/04 UPDATE: The Missoulian has a nice follow up piece today.