> http://news.yahoo.com/human-greenhouse-gas-emissions-traced-roman-tim...
> Human Greenhouse Gas Emissions Traced to Roman Times
> By Tia Ghose, LiveScience Contributor | LiveScience.com – 10/5/2012
> By burning wood, humans have been significant contributors to
> greenhouse gas emissions as far back as the Roman Empire, researchers
> say.
> The finding may lead scientists to rethink some aspects of climate
> change models, which assume humans weren't responsible for much
> greenhouse gas before the Industrial Revolution.
> "It was believed that emissions started in 1850. We showed that humans
> already started to impact greenhouse effects much before," study co-
> author Célia Sapart of Utretcht University in the Netherlands said.
> Methane is a potent greenhouse gas with 20 times the warming power of
> carbon dioxide, Sapart told LiveScience. Forest fires, wetlands and
> volcanic eruptions naturally release methane into the atmosphere. But
> human actions, such as raising cattle or burning fossil fuel, now
> account for more than half of the methane released.
> To see how far back humans were producing significant amounts of
> methane, Sapart and her colleagues analyzed ice cores from Greenland.
> Tiny air bubbles trapped in the ice provide a perfect snapshot of the
> atmosphere thousands of years ago: The fraction of heavy and light
> carbon isotopes (atoms of the same element but with different numbers
> of neutrons) inside these air bubbles can not only reveal atmospheric
> levels of methane but tell researchers whether the gas came from
> forest fires, wetlands or other sources. [Giant Ice: Photos of
> Greenland's Glaciers]
> In their Oct. 3 study detailed in the journal Nature, the researchers
> found that methane production was high around 100 B.C., during the
> heyday of the Roman Empire, and waned around A.D. 200 as the empire
> faltered. The methane was released when Romans burned down forest to
> clear land for crops and expanding settlements, Sapart said.
> This time period also coincided with the peak of China's Han dynasty,
> which burned large amounts of wood to forge swords. Once the dynasty
> collapsed around A.D. 200, atmospheric methane levels dropped.
> Methane production also spiked during Europe’s mini-ice age, around
> 1400, as people burned wood to stay toasty inside, she said. Across
> the time period the researchers studied, human activities such as
> growing food or keeping warm were responsible for 20 percent to 30
> percent of the methane released from burning organic matter. Of
> course, the historical methane emissions were still small in
> comparison with modern levels.
> The findings suggest that climate change predictions may need
> tweaking, Sapart said. Prediction models assume baseline, natural
> levels of methane emissions to forecast how human actions will change
> levels in the future. Previously, researchers thought natural events
> produced almost all of the methane prior to industrialization.
> "The big goal of all this is to try to predict how greenhouse gas
> concentrations in the atmosphere are going to evolve in the future,"
> Sapart said. "Already at this period humans were emitting greenhouse
> gases, especially methane, so we need to reconsider what are natural
> conditions.”
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