• Rice paddies, such as these terraced ones, are contributing to methane production. (Pixabay)Source: Pixabay
Some of the worst emissions culprits are not what you’d think.
By
Signe Dean

7 Oct 2016 - 3:28 PM  UPDATED 7 Oct 2016 - 3:28 PM

Earlier this month a new study drew attention to a largely ignored source of damaging greenhouse gases.

It turns out that the water reservoirs we keep for hydroelectric plants and irrigation are emitting 25 per cent more methane than previously thought, according to researchers from Washington State University.

Pools of methane

All these massive water pools that are a valuable part of our infrastructure have been producing roughly 1 gigaton of carbon dioxide equivalent emissions every year - that’s 1.3% of all human-produced greenhouse gases.

Methane, the second most abundant greenhouse gas after CO2, has even greater global warming potential, currently estimated to contribute 15 per cent to overall warming effects on the planet - and it’s the most significant gas coming out of our reservoirs.

“We had a sense that methane might be pretty important but we were surprised that it was as important as it was,” said Bridget Deemer, lead author of the study to be published in the journal BioScience. “It’s contributing right around 80 per cent of the total global warming impact of all those gases from reservoirs. It’s a pretty important piece of the budget.”

The reason reservoirs tend to contribute more methane than natural bodies of water is because they contain large amounts of organic matter, such as plant life swamped by flooding water. As this matter decomposes, it produces carbon dioxide, methane, and nitrous oxide.

“While reservoirs are often thought of as ‘green’ or carbon neutral sources of energy, a growing body of work has documented their role as greenhouse gas sources,” the authors write in their paper, considered to be the current largest study of water reservoir greenhouse gas emissions.

Belching microbes

But if water reservoirs are only just being included in our calculations of greenhouse gas emissions, some already-known methane producers have been ramping up their production of this harmful atmospheric gas.

A team of researchers from US National Oceanic and Atmospheric Administration in Boulder, Colorado, have finally tracked down the methane that’s been surging in our atmosphere since 2007.

They found that methane emissions from fossil fuels - coal mines, gas well leaks - are almost twice larger than what we previously thought. But surprisingly, they are not the culprit of the spike observed in the recent years.

Their study, published in Nature yesterday (6 October), used isotope analysis of air samples collected from around the world, and discovered that methane-producing microbes are in fact behind the current dramatic surge of this gas.

This rice paddy - probably full of methane-producing microbes.

These microbes live in tropical wetlands and heavily irrigated farms such as rice paddies, but it’s still unclear why their emissions are on the rise. However, researchers suggest it could be due to rising temperatures and more rainfall.

When it comes to methane from fossil fuels, this latest analysis actually demonstrates that the industry can really make a difference in mitigating negative effects of climate change - it just has to keep working in the right direction, controlling gas leaks and continuously curbing emissions. 

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