Burning Questions

When Jennifer Marlon and her team charted out the rate at which vegetation has burned over the past 2,000 years, they ended up with a wildly fluctuating graph that resembled a roller-coaster ride. To get to the bottom of these surprising gyrations, the researchers set out to disentangle the gnarly mix of human and climate variables that impact burning. Their study provides the first-ever comprehensive history of burning and recently appeared in Nature Geoscience. Here’s a snapshot of what it found:

Part 1: Small Bumps, Slow Drop From 1 to 1750 A.D., biomass burning declines as the global climate gradually cools.

Part 2: Uphill Beginning in 1750, fires spike sharply. With the dawn of the Industrial Revolution, increased CO2 fertilizes plant growth, adding fuel to the flames. Slash-and-burn agriculture also contributes.

Part 3: The Big Drop In 1870, burning reaches its peak and then falls precipitously. Reduced forest cover, land fragmentation, and fire-suppression policies may be the cause.

Part 4: Another Climb The authors cannot resolve records from recent decades, but other reports show an uptick in forest fires—and this time, climate change may be at fault. With each passing summer, blazes in the West are becoming more devastating. And the trend may not stop until cooling resumes or, more ominously, there’s little left to burn. ❧
—Jessica Leber

Marlon J.R. et al. 2008. Climate and human influences on global biomass burning over the past two millennia. Nature Geoscience 1(10):697-702.