President Obama’s carbon plan announced this summer finally moves the United States to take much needed steps toward reducing emissions of carbon dioxide, but unfortunately the plan largely ignores the low-hanging fruit to slow the rate of global warming: reducing emissions of methane, another type of carbon.
The president’s focus on carbon dioxide is perhaps no surprise, given the environmental community’s decades-long emphasis on this as the most important greenhouse gas. But rapid advancements in the scientific understanding of the role of methane as a driver of global warming strongly show the danger of tunnel vision on carbon dioxide.
In scientific terms, the important 2013 fifth synthesis report from the Intergovernmental Panel on Climate Change concludes that current global emissions of methane equal or exceed the global emissions of carbon dioxide, when the methane emissions are converted to their equivalency for causing global warming using an integrated 10-year time period. The actual mass of methane emitted is less than carbon dioxide, but at this decadal time scale methane traps more than 100 times more heat per mass emitted. Over 20 years, methane still traps 86 times more heat; over 100 years, 34 times more heat.
In other words: methane is a very potent form of carbon in the atmosphere.
Other research shows that because of lags in the climate system, reducing carbon dioxide pollution will have little or no influence on the rate of global warming over the coming several decades. Even in the advent of aggressive carbon dioxide controls, the planet will continue to warm to dangerous temperatures of 2.7 degrees Fahrenheit above the pre-industrial baseline within the next 15 years or so and to 3.6 degrees within 40 years. On the other hand, the Earth’s climate responds much more quickly to reductions in methane and we can greatly slow the rate of global warming during the critical next few decades by reducing methane emissions, according to a paper published in Science in 2012.
Why are these next few decades critical? As the planet warms by 2.7 to 3.6 degrees, the risk of reaching tipping points in the climate system that lead to runaway global warming become significantly greater. Some of the feedbacks that can lead to this runaway warming include melting of the Arctic permafrost and melting of methane clathrates (frozen deposits of methane) on the continental shelves of the oceans. Both of these greatly increase the “natural” flux of methane to atmosphere. The planet has already lost almost 20 percent of the area of frozen tundra over the past 20 years due to global warming, according to the National Oceanic and Atmospheric Administration, and much of this area has turned into wetlands that emit large quantities of methane. And a Swedish research cruise this summer along the continental shelf of the Arctic Ocean north of Siberia documented large amounts of methane bubbling into the atmosphere, quite likely a result of melting clathrates as the Arctic Ocean warms.
Natural gas, including both production and delivery to consumers, is the largest source of methane emissions in the United States, and increasing evidence shows that these methane emissions are growing with more development of shale gas and oil. For instance, measurements of methane concentrations in the atmosphere made from space by satellite show large increases over the major shale gas and oil plays as they were developed between 2006-2008 and 2009-2011, according to a paper to be published this fall in the American Geophysical Union’s journal Earth’s Future. My own research shows that methane emissions give natural gas – and particularly shale gas – a larger greenhouse gas footprint than coal when considered over the critically important time scale of the next few decades.
By ignoring methane, Obama’s carbon plan has the paradoxical result of encouraging replacement of coal with gas, which will aggravate global warming in the short term. We clearly need to reduce emissions of both carbon dioxide and methane. And the pathway is clear: a rapid transition to relying solely on renewable energy sources and using state-of-the art technologies to use energy more efficiently. Any other energy policy will be disastrous for the planet.
Howarth, Ph.D. is the David R. Atkinson Professor of Ecology and Environmental Biology at Cornell University.