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12,900 Years Ago: North American Comet Impact Theory Disproved

Date:
January 27, 2009
Source:
University of Bristol
Summary:
New data disproves the recent theory that a large comet exploded over North America 12,900 years ago, causing a shock wave that traveled across North America at hundreds of kilometers per hour and triggering continent-wide wildfires. Scientists tested the theory by examining charcoal and pollen records to assess how fire regimes in North America changed between 15 and 10,000 years ago, a time of large and rapid climate changes.

Scientists examined charcoal and pollen records for traces of wildfires. Their results provide no evidence for continental-scale fires, but support the fact that the increase in large-scale wildfires in all regions of the world during the past decade is related to an increase in global warming.
Credit: Copyright Tyson Paul

New data disproves the recent theory that a large comet exploded over North America 12,900 years ago, causing a shock wave that travelled across North America at hundreds of kilometres per hour and triggering continent-wide wildfires.

Dr Sandy Harrison from the University of Bristol and colleagues tested the theory by examining charcoal and pollen records to assess how fire regimes in North America changed between 15 and 10,000 years ago, a time of large and rapid climate changes.

Their results provide no evidence for continental-scale fires, but support the fact that the increase in large-scale wildfires in all regions of the world during the past decade is related to an increase in global warming.

Fire is the most ubiquitous form of landscape disturbance and has important effects on climate through the global carbon cycle and changing atmospheric chemistry. This has triggered an interest in knowing how fire has changed in the past, and particularly how fire regimes respond to periods of major warming.

The end of the Younger Dryas, about 11,700 years ago, was an interval when the temperature of Greenland warmed by over 5°C in less than a few decades. The team used 35 records of charcoal accumulation in lake sediments from sites across North America to see whether fire regimes across the continent showed any response to such rapid warming.

They found clear changes in biomass burning and fire frequency whenever climate changed abruptly, and most particularly when temperatures increased at the end of the Younger Dryas cold phase.

"We had the data to look for widespread fires if they had occurred," Jennifer R. Marlon, first author of the study and doctoral student at the University of Oregon said, "but what we saw instead was a general increase in biomass burning whenever the climate warmed."

The lakes containing the charcoal are in Alaska (3 sites), British Columbia (7), U.S. Pacific Northwest (6), the Sierra Nevada (3), northern U.S. Rocky Mountains (6), Southwest (4), Midwest (2), Northeast (3 sites in Quebec), and Southeast (1). Thirty of the samples came from the Global Charcoal Database; another five were drawn from more recent research by co-authors currently studying sediments from the Younger Dryas.

The new study's conclusion that climate is a major control of wildfires matched that of a study published last year in Nature Geosciences by the same researchers on global biomass burning over the last 2,000 years. "Together, Patrick J. Bartlein, a professor of geography at the University of Oregon said, "these studies suggest that episodes of global warming are accompanied by increases in wildfires."

Understanding whether rapid changes in climate have caused wild fires in the past will help understand whether current changes in global temperatures will cause more frequent fires at the present time. Such fires have a major impact on the economy and health of the population, as well as feeding into the increase in global warming.


Story Source:

The above story is based on materials provided by University of Bristol. Note: Materials may be edited for content and length.


Journal Reference:

  1. J. R. Marlon, P. J. Bartlein, M. K. Walsh, S. P. Harrison, et al. Wildfire responses to abrupt climate change in North America. Proceedings of the National Academy of Science, DOI: 10.1073_pnas.0808212106

Cite This Page:

University of Bristol. "12,900 Years Ago: North American Comet Impact Theory Disproved." ScienceDaily. ScienceDaily, 27 January 2009. <www.sciencedaily.com/releases/2009/01/090126173729.htm>.
University of Bristol. (2009, January 27). 12,900 Years Ago: North American Comet Impact Theory Disproved. ScienceDaily. Retrieved October 23, 2014 from www.sciencedaily.com/releases/2009/01/090126173729.htm
University of Bristol. "12,900 Years Ago: North American Comet Impact Theory Disproved." ScienceDaily. www.sciencedaily.com/releases/2009/01/090126173729.htm (accessed October 23, 2014).

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