Post-pandemic reforestation in New World helped trigger Little Ice Age

December 19th, 2008 - 3:53 pm ICT by ANI  

Washington, Dec 19 (ANI): A new analysis has suggested that post-pandemic reforestation in the New World helped trigger the Little Ice Age from 1500 to 1750.

The analysis, by Stanford University researchers detailed the amount of charcoal contained in soils and lake sediments at the sites of both pre-Columbian population centers in the Americas and in sparsely populated surrounding regions.

They concluded that reforestation of agricultural lands, which were abandoned as the population collapsed, pulled so much carbon out of the atmosphere that it helped trigger a period of global cooling, at its most intense from approximately 1500 to 1750, known as the Little Ice Age.

We estimate that the amount of carbon sequestered in the growing forests was about 10 to 50 percent of the total carbon that would have needed to come out of the atmosphere and oceans at that time to account for the observed changes in carbon dioxide concentrations, said Richard Nevle, visiting scholar in the Department of Geological and Environmental Sciences at Stanford.

Nevle and Dennis Bird, professor in geological and environmental sciences at Stanford, synthesized published data from charcoal records from 15 sediment cores extracted from lakes, soil samples from 17 population centers and 18 sites from the surrounding areas in Central and South America.

They examined samples dating back 5,000 years.

What they found was a record of slowly increasing charcoal deposits, indicating increasing burning of forestland to convert it to cropland, as agricultural practices spread among the human populationuntil around 500 years ago.

At that point, there was a precipitous drop in the amount of charcoal in the samples, coinciding with the precipitous drop in the human population in the Americas.

To verify their results, they checked their fire histories based on the charcoal data against records of carbon dioxide concentrations and carbon isotope ratios that were available.

We looked at ice cores and tropical sponge records, which give us reliable proxies for the carbon isotope composition of atmospheric carbon dioxide. And it jumped out at us right away, Nevle said.

We saw a conspicuous increase in the isotope ratio of heavy carbon to light carbon. That gave us a sense that maybe we were looking at the right thing, because that is exactly what you would expect from reforestation, he added.

During photosynthesis, plants prefer carbon dioxide containing the lighter isotope of carbon.

Thus, a massive reforestation event would not only decrease the amount of carbon dioxide in the atmosphere, but would also leave carbon dioxide in the atmosphere that was enriched in the heavy carbon isotope. (ANI)

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