Reference
Riano, D., Moreno Ruiz, J.A., Isidoro, D. and Ustin, S.L. 2007. Global spatial patterns and temporal trends of burned area between 1981 and 2000 using NOAA-NASA Pathfinder. Global Change Biology 13: 40-50.
Background
Increased wildfires are often said by climate alarmists to be caused by global warming, because somewhere on earth it is always possible to find such a trend; and in some of these cases, it is possible that rising temperatures may indeed have been involved. But what is learned when the entire world is surveyed?
What was done
The authors present "an analysis of the spatial and temporal patterns of global burned area with the Daily Tile US National Oceanic and Atmospheric Administration-Advanced Very High-Resolution Radiometer Pathfinder 8 km Land dataset between 1981 and 2000."
What was learned
For several areas of the world, there were indeed significant upward trends in land area burned. Some parts of Eurasia and western North America, for example, had annual upward trends as high as 24.2 pixels per year, where a pixel represents an area of 64 km2. These increases in burned area, however, were offset by equivalent decreases in burned area in tropical southeast Asia and Central America. Consequently, in the words of Riano et al., "there was no significant global annual upward or downward trend in burned area." In fact, they say "there was also no significant upward or downward global trend in the burned area for any individual month." In addition, they say that "latitude was not determinative, as divergent fire patterns were encountered for various land cover areas at the same latitude."
What it means
Although one can identify parts of the world that experienced increases in land area burned over the last two decades of the 20th century, for the globe as a whole there was absolutely no relationship between global warming and total area burned over this period.