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Methane Emitted by Humans Vastly Underestimated: Study

From a good vantage point and weather permitting, anyone can take in the view and see for miles on end. But what about taking a sample of air from an ice core and peering into the 18th century?

(CN) – From a good vantage point and weather permitting, anyone can take in the view and see for miles on end. But what about taking a sample of air from an ice core and peering into the 18th century?

Over the last 200 years starting with the Industrial Revolution, humans have pumped large amounts of methane into Earth’s atmosphere. A study published Wednesday in the journal Nature says previous estimates have grossly underestimated just how much humans have contributed to global warming with fossil fuels use and greenhouse gas trapped in the atmosphere.

But the findings also indicate greater reduction of emissions from humans is within our grasp.

Greenhouse gases trapped in Earth’s atmosphere vary. Carbon dioxide lingers for about a century while methane has a shorter shelf-life of about nine years, according to the study authors from the University of Rochester.

Methane can be broken down into two categories, biological and fossil methane, and can be categorized by identifying the radioactive isotope carbon-14. Naturally occurring methane released from wetlands, landfills, rice fields and livestock falls into the biological category; the fossil variety has been hidden away for millions of years in hydrocarbon deposits and released through natural geologic seeps or more commonly by humans and drilling. The fossil methane does not have carbon-14, according to study authors.

The team used a sample from an ice sheet in Greenland that dated to before the start of the Industrial Revolution. The results show methane emissions at 1.6 teragrams (a teragram understood to represent 1 trillion grams) per year – far less than the 38 to 58 teragrams per year that had been previously estimated.

Which means human emissions of methane are 25% to 40% higher than previously estimated.

Co-author Vasilii Petrenko, earth and environmental science professor at the University of Rochester, said in a statement it has been a struggle for the scientific community to understand the amount of methane emitted by humans that goes into the atmosphere.

“We know that the fossil fuel component is one of our biggest component emissions, but it has been challenging to pin that down because in today's atmosphere, the natural and anthropogenic components of the fossil emissions look the same, isotopically,” said Petrenko.

Postdoctoral associate Benjamin Hmiel and collaborators found that biological or naturally occurring methane made up most of what was found in the atmosphere up until around 1870.

That’s when fossil fuels entered the equation. According to the study authors, naturally released fossil methane are about 10 times lower than previous research reported, which would mean the manmade fossil footprint or presence in the atmosphere is much higher than previously measured.

Because methane has a much shorter lifespan in the atmosphere, he’s optimistic about the study’s findings.

“I don't want to get too hopeless on this because my data does have a positive implication: most of the methane emissions are anthropogenic, so we have more control. If we can reduce our emissions, it's going to have more of an impact,” said Hmiel.

Hmiel and Petrenko did not immediately respond to emails for follow up questions on their study results.

Categories / Environment, Science

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