One of the great challenges in assessing the meaning of changes in Arctic climate and other environmental conditions is putting today’s observations in long-term context. This is as true for the bubbling emissions of methane from the frozen, but warming, sea bed as for sea ice around the North Pole. Two recent studies of methane emissions from frozen sea-bed sediments, including one published in Science and described in The Times today, found substantial bubbling flows of methane, a potent greenhouse gas, were reaching the atmosphere. In its news release, the National Science Foundation, which helped underwrite the research, described the emissions as taking place “ at an alarming rate.”
But are these emissions new, or simply newly observed? Does this mean that the Arctic system is coming unglued, and that a great outpouring of this heat-trapping gas is about to upend the global climate system?
Despite portentous headlines — including one on the news release from the University of Alaska, Fairbanks, saying “ Arctic seabed methane stores destabilizing…” — there is no evidence (yet) that what is happening is fundamentally new or destabilizing, at least according to some of the scientists most closely tracking levels and sources of this gas from the poles to the tropics. Here’s how Ed Dlugokencky, one of the top federal scientists tracking methane trends, summarized the situation in an e-mail message:
Are these emissions new, brought on by increasing temperature of bottom waters, or have they been there unnoticed for decades or longer? Based on our atmospheric observations, I suspect they have been there. We saw an increase in CH4 growth rate in 2007 in the Arctic (likely from very warm temperatures in wetland regions increasing microbial CH4 production), but it did not increase in 2008.
Also, the difference in annually averaged CH4 between Arctic and Antarctic latitudes is a sensitive indicator of changing CH4 emissions at high northern latitudes. The only persistent large change in this difference we’ve observed was from 1991 to 1992 when the economy of former Soviet Union collapsed. The difference has varied since then, but has not recovered.
Dr. Dlugokencky has told me previously that, for the moment, it appears that methane releases from warming Arctic soils and other sources constitute a potentially amplifying warming influence, in which warming releases more gases that contribute to further warming. Such a “positive feedback” adds to the logic for working to limit human-driven warming, many climate scientists say.
But Dr. Dlugokencky, like quite a few other scientists assessing Arctic warming, sees no evidence for a “ tipping point” beyond which this cascades uncontrollably. That doesn’t mean this is impossible, just that there’s no evidence pointing to such a prospect.
Martin Heimann, who wrote an accompanying analysis in Science and is a researcher at Germany’s Max Planck Institute for Biogeochemistry, sent this cautionary note:
Indeed, at this point, it is impossible to tell whether these Arctic emissions are directly caused by recent Arctic warming or whether they have been persistent over at least much of the Holocene. This can only be answered from longer time series; complemented, maybe by borehole measurements in this shelf permafrost. Therefore, these new emission estimates do not allow yet a quantification of the permafrost methane-climate feedback.
Personally, I do believe that this feedback exists, but it doubt very much that it is “catastrophic” with large emissions over relatively short time scales (20-50 years) as implied by the “tipping point” metaphor. Even under strong warming the melting of permafrost takes time and the release of greenhouse gases will be quite gradual and will manifest itself as increased leakages.
Can society grasp the basics here without having to be pummeled with messages overstating the case? Given the seductive power of the front-page thought, scientists, their institutions and grant providers can — wittingly or unwittingly — drive overheated media coverage that, in the end, can kick back and undercut credibility.
One thing that would help clarify Arctic trends and their causes is more monitoring of methane on the ground in and around the Arctic, Dr. Dlugokencky and other researchers say.