Reference
Marlon, J.R., Bartlein, P.J., Carcaillet, C., Gavin, D.G., Harrison, S.P., Higuera, P.E., Joos, F., Power, M.J. and Prentice, I.C. 2008. Climate and human influences on global biomass burning over the past two millennia. Nature Geoscience 1: 697-702.
Background
The authors report that "large, well-documented wildfires have recently generated worldwide attention, and raised concerns about the impacts of humans and climate change on wildfire regimes," noting that "climate-change projections [our italics] indicate that we will be moving quickly out of the range of the natural variability of the past few centuries."
What was done
To see what the global wildfire "range of natural variability" has actually been in this regard, Marlon et al. used "sedimentary charcoal records spanning six continents to document trends in both natural and anthropogenic biomass burning [over] the past two millennia."
What was learned
The international team of researchers reports that "global biomass burning declined from AD 1 to ~1750, before rising sharply between 1750 and 1870," after which it "declined abruptly." In terms of attribution, they say the initial long-term decline in global biomass burning was due to "a long-term global cooling trend," while they suggest that the rise in fires that followed was "linked to increasing human influences." With respect to the final decline in fires that took place after 1870, however, they note it occurred "despite [our italics] increasing air temperatures and population." As for what may have overpowered the tendency for increased global wildfires that would "normally" have been expected to result from the global warming of the Little Ice Age-to-Current Warm Period transition, the nine scientists say they attribute the "reduction in the amount of biomass burned over the past 150 years to the global expansion of intensive grazing, agriculture and fire management."
What it means
In spite of evidence from prior centuries that global warming may indeed have had a tendency to promote wildfires on a global basis (since global cooling had a tendency to reduce them), technological developments during the industrial age appear to have overpowered this natural tendency to the point that man has become a dominant factor for good in actually leading to a decrease in global wildfires over the past century and a half.