Science Express: Warming and Earlier Spring Increases Western U.S. Forest Wildfire Activity (July 2006). Science Express is the online advance version of the journal Science.
From the abstract: "We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it to hydro-climatic and land-surface data. Here, we show that large wildfire activity increased suddenly and dramatically 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.
One author, Thomas Swetnam, director of the Laboratory of Tree-Ring Research at The University of Arizona in Tucson: "We're showing warming and earlier springs tying in with large forest fire frequencies. Lots of people think climate change and the ecological responses are 50 to 100 years away. But it's not 50 to 100 years away -- it's happening now in forest ecosystems through fire." :: ScrippsNews : Warming Climate Plays Large Role in Western U.S. Wildfires, Scripps-led Study Shows. (July 6, 2006).
The researchers also suggested that increasing fires could change forests from net consumers of CO2 to net emitters of atmospheric CO2, further adding to global warming and increasing fire danger. More Large Forest Fires Linked to Climate Change (July 6, 2006)
Serendipitously, Dr. Gavin A. Schmidt posted at RealClimate.org a brief explanation of "tipping points" in the context of positive feedback loops in complex systems. He specifically related it to climatological changes and emphasized that in systems as large and complex as the global climate, there are multiple sub-systems in which local or regional tipping points may occur. His posting is relevant to the study noted above, and the author's observation.
He says in his post:
"The idea is that in many non-linear systems (of which the climate is certainly one), a small push away from one state only has small effects at first but at some 'tipping point' the system can flip and go rapidly into another state. This is fundamentally tied to the existence of positive feedbacks and is sometimes related to the concept of multiple 'attractors' (i.e. at any time two different 'states' could be possible and near a transition the system can flip very quickly from one to another). * * * A positive feedback occurs when a change in one component of the climate occurs, leading to other changes that eventually "feeds back" on the original change to amplify it." RealClimate » Runaway tipping points of no return (July 5, 2006)