INCREASED FIRE RISK ASSOCIATED WITH THE TRIASSIC-JURASSIC BOUNDARY GLOBAL WARMING EVENT

Fire has had a major influence on Earth's systems since the Carboniferous. The composition of forest biomass, as well as its distribution and flammability, are key factors that determine fire regime, such that many of the world's ecosystems can be considered fire-dependant. Numerical models suggest that the annual number of fires in the U.S. will increase by 44%, with a 78% increase in the area burned by fires in response to predicted future climate change (2xCO₂). Here we test the hypothesis that fire activity is likely to increase in response to global warming and aim to provide measured data for testing the output of numerical models of future fire threat. We have used fossil charcoal abundance as a proxy for ancient fire activity across the Triassic-Jurassic global warming event (Tr-J; 200Ma; 3xCO₂), and report a six fold increase in fire activity in the earliest Jurassic of east Greenland. We show that at the same time and location, the vegetation shifted from dominantly broad-leafed to dominantly narrow-leafed plants. In order to examine whether the observed changes in dominant gross leaf morphology could have lead to increased fire activity, modern analogues of the fossil plants from the Tr-J of east Greenland have been tested for flammability using state-of-the-art fire propagation apparatus. Our analyses reveal increased flammability associated with narrow leaf morphologies. On the basis of these results, we attribute the increase in observed fire activity to a climate-driven shift from dominantly broad- to dominantly narrow-leafed morphologies across the Tr-J boundary. In combination, our results suggest that global warming events have the potential to lead to significant increases in fire activity.