Humans use fire for heating, cooking, managing lands and, more recently, fueling industrial processes. Now, research from the University of Colorado has found that these various means of using fire are inversely related to one another, providing new insight into how people are changing the face of fire. The results were published in the journal Philosophical Transactions of the Royal Society B and presented at a meeting of the Royal Society in London as part of a discussion on fire and mankind.

Over time, the majority of human fire use has shifted from indigenous burning to agricultural burning to fossil fuel burning. The findings show that locations on the planet with high fossil fuel emissions and biomass burning emissions are rare, suggesting an inverse relationship in which an increase in one causes a decline in the other.

"We call this the 'combustion ladder' - where fire management shifts towards using more efficient and safer forms of combustion that may ultimately exclude open use of fire in the landscape," said Jennifer Balch, director of Earth Lab and assistant professor in the Department of Geography at CU-Boulder and lead study author.

The new study, which incorporates satellite data on fire with fossil fuel emissions data from a 14-year period between 1997 and 2010, marks one of the first times this shift has been tested with global data.

"One important next step is to distinguish between natural landscape fires, fires started accidentally by humans and fires deliberately started as part of land management," said Andrew Scott, a professor at the Royal Holloway University of London and a co-author of the study.

"Despite our push to contain combustion, there are still fires in places that can be very damaging," said Balch. "We've tried the experiment in the U.S. of trying to remove fire completely, and it doesn't work. We spend two to three billion dollars every year fighting fires. In the western U.S. in particular, we live in flammable places, and must learn to coexist with fire."

Other co-authors on the new study include Chelsea Nagy of CU-Boulder; Sally Archibald of the University of the Witwatersrand (South Africa); David Bowman and Grant Williamson of the University of Tasmania (Australia); Max Moritz of the University of California, Berkeley; and Christopher Roos of Southern Methodist University.