Nature Geosci. doi:10.1038/ngeo313 (2008)

Forest fires, whether natural or started by humans, declined worldwide during most of the past 2,000 years in parallel with global cooling. According to a new analysis, biomass burning increased only between ad1750 and 1870, when the climate started to become warmer, populations grew rapidly, land use changed as agriculture intensified, and the industrial revolution raised atmospheric levels of carbon dioxide.

Jennifer Marlon at the University of Oregon, Eugene, and her colleagues used records of charcoal in sediments from 406 lakes, bogs and small hollows across six continents to reconstruct trends in wildfires. Wildfires declined again after 1870 as a result of landscape fragmentation and of fire management in the twentieth century.

The increase in wildfire frequency that has been observed during the past three decades — attributed to current global warming — is not yet represented in the sediment record.