Wildfire response to rapid climate change
24 March 2009, by Matthew Aylott
Scientists investigating the effects of a comet that reportedly exploded over North America 12,900 years ago, find no evidence of widespread fires associated with the impact.
It seems large comets did not cause widespread fires in North America as previously suggested.
It had been suggested that one or more comets exploded over northern North America and sent shockwaves across the continent, triggering wildfires and resulting in the disappearance of North America's biggest animals including the mammoth and saber-toothed tiger.
But new research published in the Proceedings of the National Academy of Sciences finds no evidence of fires at the time of the impact. Instead researchers found clear changes in plant burning and the frequency of wildfires when the climate changed abruptly, particularly as temperatures increased.
At the end of the last Ice Age several sudden events triggered rapid changes to the climate; temperatures above Greenland increased by over 5°C in just a few decades. This temperature jump happened at the end of a 1200-year-long cold period called the Younger Dryas stadial.
Comets not culprits
The new research, conducted by 23 scientists from around the world, was to discover whether wildfires across the continent responded to such rapid warming. They also looked for evidence of continental-scale fires at the beginning of the Younger Dryas cold period 12,900 years ago, the time of the comet impact. To determine the changes in fire activity, pollen samples from charcoal accumulated in sediments of 35 North American lake beds were dated.
The charcoal data suggests an important role for climate, and particularly rapid climate change, in determining levels of fire activity. Charcoal remains indicate temperatures were a few degrees warmer than in North America today and this had a marked effect on the number of fires. They found fires gradually and steadily rose prior to the Younger Dryas cold period and peaked around 13,200 years ago, in response to increasing temperatures. A fact consistent with observed increases in temperature and fires over the past few decades in North America. However, there was no continent-wide fire response at the beginning of the Younger Dryas.
Large scale fires can have a major impact on the economy, population health and can increase global warming. Understanding the impact of rapid climate change on the frequency and severity of wildfires in the past could help us understand the effect current changes in global temperatures will have on future fires.
Co-author Professor Sandy Harrison from the University of Bristol explains, 'Some climate models have shown a shutdown of the thermohaline circulation [the ocean circulation that helps maintain north-west Europe's temperate climate] under future climate scenarios. If this happens, it could have big implications for fires in Europe.'
Harrison adds, 'We hope that our insights into the system will yield useful information for managing and adapting to future environmental changes.'
This research was carried out by an international team of scientists from six different countries and supported by the Natural Environment Research Council's £20 million QUEST (Quantifying and Understanding the Earth System) programme.
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