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Globe-warming methane emissions may be canceling gains on carbon dioxide

After a period of stability, researchers find a big acceleration — and a complicated challenge for control efforts.

Jackson and Saunois feel that about 60 percent of total emissions worldwide can be classed as anthropogenic, with agriculture contributing about one-third of that; major sectors are beef and rice production.
REUTERS/Marcos Brindicci

Atmospheric levels of methane, long considered the second most threatening of the globe-warming greenhouse gases, have been surging for almost a decade — and at a rate that accelerated steeply in 2014 and 2015.

This is the conclusion of two new papers published Monday, and a presentation Tuesday to the American Geophysical Union’s meeting in San Francisco, in which researchers conclude that that the methane acceleration may be canceling out the benefits of carbon dioxide’s recent slowdown.

Also, that the current emission rates lie far outside the assumptions of all models and forecasts about the pace of global warming and its climate impacts.

A lead author of both papers is Rob Jackson, an earth scientist from Stanford University, who has become known in recent years for his work on many facets of the methane problem. He takes a more complex view than some of the contributions from oil and natural gas production, while raising alarms about leaks from municipal supply lines, and stressing that methane routinely receives too little attention compared to CO2. As Stanford’s announcement of the papers points out,

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Methane’s warming potential is about 28 times greater [than CO2] on a 100-year horizon, and its lifespan in the atmosphere is much shorter. In other words, it can do major damage, but getting it under control could tip the climate change equation relatively rapidly.

“Methane presents the best opportunity to slow climate change quickly,” said Jackson. “Carbon dioxide has a longer reach, but methane strikes faster.”

But methane also presents more complex control problems than CO2 for multiple reasons, these two in particular:

  • While science has a good understanding of atmospheric carbon’s sources, especially emissions from the burning of coal, oil and natural gas, methane emissions come from a range of manmade and natural sources that complicate attribution — not to mention control strategies. Same for methane “sinks” that remove it from the atmosphere.
  • Measurement, too, remains a little rough, which adds additional layers of approximation to most efforts to attribute emissions and design controls.

Jackson and the papers’ main author, Marielle Saunois of France’s Laboratoire des Sciences du Climate et de l’Environnement, are leading voices in the circle of scientists concerned with methane. They are also leaders of the Global Methane Budget project, which every two years publishes an updated report on methane levels in the atmosphere.

This year’s findings were was published in the open-access journal Earth System Science Data, and a separate discussion of the findings and their implications was published simultaneously as an editorial in Environmental Research Letters.

A tenfold rise in emissions rate

Before the rise of industrialization, atmospheric levels of methane are thought to have been in the neighborhood of 700 parts per billion. The new papers put the current level at 1,840 ppb, but the size of that increase is not as significant as the recent growth trend.

From 2000 to 2006, methane levels didn’t change much, increasing about one-half part per billion per year. But that rate grew tenfold in the next nine years, averaging 6.9 ppb from 2007 to 2015, and reaching 12.5 ppb in 2014 before subsiding a bit to 9.9 ppb the following year.

Jackson and Saunois feel that about 60 percent of total emissions worldwide can be classed as anthropogenic, with agriculture contributing about one-third of that; major sectors are beef and rice production because of breakdown processes in the cattle gut and the paddies’ muck. Energy production and mining are thought to produce another third, and the rest comes from sources that include landfills and the burning of both fossil and biofuels.

But there are also many natural sources where human influence is essentially absent, like seabed seeps and decomposition in wetlands, or less direct, like permafrost melt.

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Geographically, methane’s sources are also very different from the carbon associated with industrial fuel consumption; about two-thirds of emissions originate in the tropics, where wetlands are the prime contributor.

Like CO2, atmospheric methane is lowered by various “sinks” — chemical radicals in the air can oxidize it, and soil organisms can consume it — but these, too, are not as well understood as, say, carbon sequestration in trees and other plants.

Part of the rise in methane, the researchers say, could reflect a change in the workings of these sinks. For example, atmospheric concentrations of a methane-killing hydroxyl radical known to have been  increasing since at least the 1970s have been flat since 2006. But nobody really grasps the whole picture.

These various factors notwithstanding, there is no consensus scenario of methane sources and sinks that explains the atmospheric increase since 2007. Recent evidence from atmospheric observations suggests three main contributors for emission changes.

The first element is an increase in biogenic emissions, mostly from agriculture. The second is an increase of fossil-related emissions. The third is a decrease of biomass burning emissions. …

At the regional scale, methane emissions contributing to the observed atmospheric increase since 2006 are most likely tropical, although some mid-latitude regions, such as China, also appear to contribute to the increase. To date, no significant contribution to the atmospheric increase from Arctic regions has been found, except in 2007 and attributable then to a relatively warm and late summer. Contrary to a recent estimate based on three different atmospheric inversions, no trend in U.S. methane emissions is found … and thus a substantial contribution of U.S. shale gas industry to the recent methane atmospheric increase seems unlikely.

How the energy sector contributes

Critics of fracking may find that last point a little hard to swallow, but the Saunois-Jackson work is not the first report this year to make it.

Back in October, a fine perspective piece by John Fialka in E&E News reported on research findings published in the journal Nature that “while gas production has soared in recent years, the industry’s rate of leakage appears to have declined.”

As has been widely discussed, here and elsewhere, shocking amounts of methane have been released through the industry practices of venting raw gas from working wells, from faulty valves and pipeline controls, and from mothballed operations that weren’t sealed properly. However, it appears that because of a combination of new regulations and voluntary changes in practice, that has begun to change, with more progress likely as the U.S. Environmental Protection Agency updates both its measurement approaches and its monitoring.

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Interestingly, Fialka finds that concern over global warming hasn’t been the biggest driver here:

Questions about the impacts of natural gas leaks first surfaced in Washington, D.C., in 2004. U.S. EPA had been concerned for years because the largest component of natural gas is methane, a potent greenhouse gas often released into the atmosphere as the result of human activities. It appears to be artificially warming the Earth.

That issue did not resonate deeply within Congress or the George W. Bush administration, but in 2004, the Government Accountability Office found a related matter that did: Oil and gas production on U.S. public lands generates about $9 billion annually, making it one of the largest non-tax sources of federal funds. The resource is overseen by the Interior Department, which is legally required to collect royalty payments and to make sure the public’s resources are not being wasted….

[GAO found that] the United States had lost $58 million in federal royalty payments in 2008. With proper management, 40 percent of the lost gas might have been recovered and sold. The fugitive emissions of methane and CO2 were comparable to the emissions of 8 million passenger cars or 10 average-sized coal-fired power plants.

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The Saunois-Jackson papers can be read here and here without charge.