Methane in the Earth's atmosphere is an important greenhouse gas, so far accounting for about 20 percent of the global warming caused by human activity — more than any other gas except CO2. It has a global warming potential of 25 over a 100-year period, meaning that a methane emission will have 25 times the impact on temperature of a CO2 emission of the same mass over the next 100 years. Methane has a big impact over a brief period — a lifetime of about 12 years in the atmosphere — whereas CO2 has a smaller impact for a far longer period of more than 100 years. An estimated 60 percent of the Earth’s methane emissions are attributable to human activity, with landfills, livestock husbandry, fossil fuel development, and rice agriculture as major causes.
Methane is also naturally released by the decay of organic matter in wetlands. Less significant natural sources include termites, oceans, and release from methane deposits buried deep within the Earth. Currently, the amount of methane released by those deposits is slight in comparison to other sources — but shifts in the planet’s stability, of the magnitude expected from continued rapid global warming, could cause massive releases of stored methane. In particular, Arctic methane could prove to be the linchpin for runaway global warming. Thousands of years ago, billions of tons of methane were created by decaying Arctic plants, which now lies frozen in permafrost and trapped in the ocean floor. As the Arctic warms, this methane will likely be freed, greatly accelerating warming.
Analysis of air bubbles trapped in ice sheets shows that methane is more abundant in the Earth’s atmosphere now than at any time during the past 400,000 years. Global average atmospheric concentrations of methane have increased from approximately 700 parts per billion by volume in 1750 — at the time of the Industrial Revolution — to roughly 1,800 parts per billion in 1998. Levels of the gas in the atmosphere had held steady since 1998, then suddenly spiked in 2007, when National Oceanic and Atmospheric Administration studies show they increased by 27 million tons. Researchers confirmed this finding in October 2008; they believe that unusually warm conditions over Siberia affected methane levels in the Northern Hemisphere by increasing the amount of methane produced by bacteria in Siberian wetlands.
Scientists are not sure whether the methane spike signals the beginning of a long-term, massive release or is a one-time blip, but say that given methane’s power to warm the climate, even a small increase is cause for concern.
Unleashing the methane reservoir could potentially warm the Earth tens of degrees; a violent opening of this “methane ice” (also known as clathrates), according to some scientists, may have triggered a catastrophic climate change and reorganization of the ocean and atmosphere around 635 million years ago.
The U.S. Environmental Protection Agency estimates that methane volumes equivalent to taking 90 million cars and light trucks off the road could be achieved globally by 2020 at a cost benefit or at no cost. In the United States alone, that would be the equivalent of taking more than 12 million cars and light trucks off the road. And the EPA analysis doesn’t even include the value of significant air-quality and health benefits that would accompany methane reductions: Studies have found that reducing global methane emissions by 20 percent would save 370,000 lives between 2010 and 2030, due to the decrease in ozone-related cardiovascular, respiratory, and other health impacts.
EPA may be underestimating available no-cost and low-cost methane mitigation options, but even its conservative analysis clearly demonstrates the opportunities available in methane control. Enormous reductions can be achieved with currently available technology, while mandatory greenhouse gas regulation would speed the development and deployment of new technology and mitigation options, making much deeper reductions feasible in the near future.
But the key is rapid action: Methane needs to be dealt with immediately through strong regulation to sharply restrict emissions. Because of the urgency of the problem, and the need to address methane now, longer-term attempts to address the crisis will not be sufficient.
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