US emitting 50% more methane than EPA calculations: Study

By Salome Phelamei | Last Updated: Tuesday, November 26, 2013 - 20:03

Zee Media Bureau

Washington: The emissions of methane in the United States may be 50% more than the indicated estimates by the US Environmental Protection Agency (EPA), says a new study on Monday.

The study published in this week’s issue of the Proceedings of the National Academy of Sciences says the EPA may not be including all sources of methane gas being released by the US.

Methane- considered as a greenhouse potent was first discovered by Italian physicist Alessandro Volta in November 1776, who, after reading a paper by Benjamin Franklin about “flammable air,” was inspired to search for the substance in the marshes at Lake Maggiore. Volta captured the gas rising from the marsh, and by 1778 had isolated the pure gas. He also demonstrated means to ignite the gas with an electric spark.

“Our numbers for the entire United States are about a factor of 1.5 times larger than the [estimates of] the EPA,” says the study’s co-author Scot Miller, a doctoral student at Harvard University.

The researchers said the most striking discrepancy was in the oil-producing south-central United States, where their results were found to be nearly three times higher than the EPA estimates.

The researchers also said that the dissimilarity in figures from the government ones may be due to difference in methodology.

Methane is released by livestock, natural gas production and distribution, coal mining, among other natural and ma-made activities, but humans are believed to contribute around 60% of the total, explained the authors.

Usually, the EPA uses a “bottom-up” approach that multiplies amounts typically released, for example, by each cow, per unit of coal, or per unit of natural gas sold.

In the new study, researchers instead took the “top-down” measurements, estimating the actual content of methane in the air and then tracing it to its sources using meteorological and statistical analysis. For the study, researchers also took almost 13,000 measurements directly from the atmosphere in 2007 and 2008.

According to Miller, the top-down approach still has its weaknesses.

“When we measure methane gas at the atmospheric level, we’re seeing the cumulative effect of emissions that are happening at the surface across a very large region,” said Steven Wofsy, a Harvard professor and co-author of the PNAS study.

“That includes the sources that were part of the bottom-up inventories, but also the things they didn’t think to measure,” he explained.

According to researchers, methane is the second-most important greenhouse gas after carbon dioxide.



First Published: Tuesday, November 26, 2013 - 19:35

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