in median annual averaged area burned in the western United States due to a 1ºC global average temperature increase, using the temperature and precipitation patterns from the corresponding figures in Chapter 4. The increase in median annual area burned ranges from 73% to over 600%, depending on the ecoprovince. Aggregating all 14 ecoprovinces in which fire is most sensitive to temperature variations, the net area burned by the median fire increases from 572,000 ha for the reference period 1970-2003, to 1,800,000 ha with a 1ºC global average temperature increase.

Other investigators using different climate models and a variety also find thata climate change will increase the risk of wildfire throughout the western United States, so long as fuel is not limiting. For example, Spracklen et al. (2009) used output from the GISS AGCM coupled to a slab ocean forced by the A1B emission scenario with an empirical model very similar to that used by Littell et al. (2009); they concluded that climate changes projected for the mid-21st century would result in a 54% increase in total annual area burned compare to that in the late 20th century, and burn areas doubling in the Rockies and Pacific Northwest.

Similar studies have been done to examine how climate change will affect forest wildfires in other regions of the world, including Australia, New Zealand, the southern Mediterranean, and in boreal forests of Canada (IPCC, 2007d). In general, these studies report wildfires will increase over the course of the century due to projected climate changes from one or more of the AR4 climate models using one or more of the marker emission scenarios.

As the time horizon increases, a further complication arises in projecting wildfires because of the importance of fuel availability and quality (moisture content) for determining the likelihood and size of wildfires. Systematic climate changes will inevitably alter the distribution of the vegetation, and significant changes in the vegetation would greatly affect the potential for wildfires and the wildfire area burned. For example, if climate change further dries already arid grasslands, then the grasslands will wither to deserts and fire will no longer be supported. On the other hand, if climate change changes the distribution of pest and pathogens such that forests become diseased, then additional fuel will be made available due to forest dieback (see, e.g., discussion of the bugs in the BC/AK spruce) and fires will be enhanced until the extra fuel is exhausted and replaced by woodlands or grasslands. To date, all of the statistical models for wildfire do not admit changes in vegetation type due to the ecosystem response to climate change.

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