Reference
Yang, J., Tian, H., Tao, B., Ren, W., Kush, J., Liu, Y. and Wang, Y. 2014. Spatial and temporal patterns of global burned area in response to anthropogenic and environmental factors: Reconstructing global fire history for the 20th and early 21st centuries. Journal of Geophysical Research: Biogeosciences 119: 249-263.
Background
The authors begin by noting that fire is a critical component of the biosphere that "substantially influences land surface, climate change and ecosystem dynamics." And, therefore, they say that to accurately predict fire regimes in the 21st century, "it is essential to understand the historical fire patterns and recognize the interactions among fire, human and environmental factors." But until now, they indicate that few efforts have been directed to studying long-term fire histories and the roles played by anthropogenic and environmental factors on a global scale.
What was done
In an attempt to provide what had previously been lacking in this regard, Yang et al., as they describe it, "developed a 0.5° x 0.5° data set of global burned area from 1901 to 2007 by coupling the Global Fire Emission Database version 3 with a process-based fire model and conducted factorial simulation experiments to evaluate the impacts of human, climate and atmospheric components."
What was learned
The seven scientists found that (1) "the average global burned area was about 442x104 km2/yr during 1901-2007," with (2) "a notable declining rate of burned area globally (1.28x104km2/yr)," that (3) "burned area in the tropics and extra-tropics exhibited a significant declining trend, with no significant trend detected at high latitudes," that (4) "factorial experiments indicated that human activities were the dominant factor in determining the declining trend of burned area in the tropics and extra-tropics," that (5) "climate variation was the primary factor controlling the decadal variation of burned area at high latitudes," that elevated CO2 and nitrogen deposition (6) "enhanced burned area in the tropics and southern extra-tropics," but that (7) they "suppressed fire occurrence at high latitudes."
What it means
All things considered, Yang et al.'s study makes it crystal clear that mankind's various activities constitute by far the most important single factor among the many that have resulted in a net century-long history of ever-decreasing global burned area.