A combination of historical ice core data and air monitoring instruments reveals a consistent trend: global atmospheric methane concentrations have risen sharply in the past 2000 years. NASA Earth Observatory image by Joshua Stevens, using data from the EPA. Graphic: Joshua Stevens

By Adam Voiland
8 March 2016

(NASA) – For a chemical compound that shows up nearly everywhere on the planet, methane still surprises us. It is one of the most potent greenhouse gases, and yet the reasons for why and where it shows up are often a mystery. What we know for sure is that a lot more methane (CH4) has made its way into the atmosphere since the beginning of the Industrial Revolution. Less understood is why the ebb and flow of this gas has changed in recent decades.

You can find the odorless, transparent gas miles below Earth’s surface and miles above it. Methane bubbles up from swamps and rivers, belches from volcanoes, rises from wildfires, and seeps from the guts of cows and termites (where is it made by microbes). Human settlements are awash with the gas. Methane leaks silently from natural gas and oil wells and pipelines, as well as coal mines. It stews in landfills, sewage treatment plants, and rice paddies.

In recent years, the gas has started to turn up in some surprising places. Nighttime satellite images show points of light—some of them gas flares—in rural parts of North Dakota, Texas, and Colorado. Mysterious craters venting methane have appeared in Siberia’s Yamal Peninsula. In October 2014, scientists announced they had discovered satellite signals of a methane hotspot over the Four Corners region of the United States. Radar observations have shown bubbles of methane rising from the depths of the Arctic Ocean. And eye-popping videos on the Internet show scientists lighting methane-rich Alaskan lakes on fire.

The long-term, global trend for atmospheric methane is clear. The concentration of the gas was relatively steady for hundreds of thousands of years, but then started to increase rapidly around 1750. The reason is simple: increasing human populations since the Industrial Revolution have meant more agriculture, more waste, and more fossil fuel production. Over the same period, emissions from natural sources have stayed about the same.

But if you focus on just the past five decades—when modern scientific tools have been available to detect atmospheric methane—there have been fluctuations in methane levels that are harder to explain. Since 2007, methane has been on the rise, and no one is quite sure why. Some scientists think tropical wetlands have gotten a bit wetter and are releasing more gas. Others point to the natural gas fracking boom in North America and its sometimes leaky infrastructure. Others wonder if changes in agriculture may be playing a role.

“There is no question that methane is doing some very odd and worrying things,” said Euan Nisbet, an atmospheric scientist at Royal Holloway, University of London. The big question is why. Scientists wonder if they will have the right monitoring systems in place to answer that question adequately. [more]

Methane Matters: Scientists Work to Quantify the Effects of a Potent Greenhouse Gas

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