Near-term evolution of arctic methane release

Those who discuss Arctic methane emissions often jump to dramatic considerations of methane hydrate deposits there. Whether or not we are preconditioning significant hydrate deposits for inevitable future releases should be a major concern, but currently hydrate is likely not the major source of Arctic methane emissions. This tendency to concentrate too much on hydrates is, ironically, not only true of those who sensationalize the threats of sudden warming, but even of those striving to take an extremely measured tone in discussing the inherently huge risks at hand, such as The World Wildlife Fund’s major report, Arctic Climate Feedbacks: Global Implications.

1250, however, being a group focused on near-term climate, is concerned with the potential for relatively small step-increases in Arctic emissions, and how such small steps might interact with our emissions mitigation strategies, altering our immediate options.

What is said too infrequently in such discussions is that an uncomfortably high proportion of current estimated Arctic methane releases come from sources which are very poorly understood, and that could conceivably change considerably in the very near future. For example, both the HIPPO program and researchers at the Wegener Institute have estimated emissions from an unexpected source – the ocean surface itself – which demands far more scrutiny in predicting near-term evolution of Arctic conditions.

This is the opposite of discussing the drama of methane hydrate – it is a very mild source of methane emission, and is very diffuse. However, it is deeply dependent upon sea surface conditions, which are rapidly changing with changes in summer sea ice cover, and thus has high potential for very large changes in its emissions rate in the very near future. The estimates of current emissions make this source currently about the same as the total combined emissions from subsea permafrost, free gas and hydrates which have, cumulatively, been widely discussed in the media, stemming from the research of Natalia Shakhova, Igor Semiletov and others, and usually attributed in the media mistakenly to methane hydrates. The hypothesized but somewhat mysterious biochemistry of this surface production is based on the assumption that shifts in the N:P (nitrogen to phosphorous) ratio (one of the so-called Redfield ratios) make aerobic methanogenesis (that is, the creation of methane in the presence of oxygen) possible in Arctic surface waters, and the estimates are that this is probably releasing about 8 million tons of methane annually now.

Could such emissions suddenly increase? If losses of sea ice induce further emissions from this source, then increases could be quite considerable. It must be remembered that the sea ice extent losses of the coming few years could cover as large a region as all the losses of the last thirty years.

How do we contextualize the current emissions from this source, and their potential for increase, within Arctic total methane emissions today? One reason for current controversy about Arctic methane emissions is because there is little concurrence between the top-down and bottom-up approaches to estimating emissions. Major global methane researchers like Ed Dlugokencky at NOAA use relatively blunt top-down metrics, like the so-called “IPD,” or inter-polar difference, estimating the methane difference from global average stretching from 53º-90ºN (it might be more useful to consider just ~67º-90ºN) and then attempting to further constrain sources through isotopic analysis (unfortunately, not yet a very evolved technique for atmospheric methane readings). On the other hand, there are burgeoning attempts to make bottom-up estimates of Arctic methane releases – for example, Katey Walter Anthony and colleagues for land-based emissions, and Shakohva and Semiletov for some sea-based ones – and from these bottom-up estimates it would appear that current Arctic contributions are likely larger than assumed by top-down estimates. Despite the uncertainties, it would be fair to say that the surface ocean emission of methane is possibly as high as 25% of all current Arctic methane emissions, a fact which is almost never discussed.

Stephen Wofsy of Harvard University, a researcher in the HIPPO program, noted that “We observed that the ocean surface releases methane to the atmosphere all over the whole of the Arctic Ocean.” At the same time, highly detailed research and modelling at the Alfred Wegener Institute suggests that these surface emissions can be traced to Arctic surface waters of Pacific origin only, but this still involves an immense area, and thus the very large expected changes in summer sea ice could very significantly impact these emissions very quickly.

Eric Kort, who led the HIPPO work, has said,

While the methane levels we detected weren’t particularly large, the potential source region, the Arctic Ocean, is vast, so our finding could represent a noticeable new global source of methane. As Arctic sea ice cover continues to decline in a warming climate, this source of methane may well increase. It’s important that we recognize the potential contribution from this source of methane to avoid falsely interpreting any changes observed in Arctic methane levels in the future.

At the same time, we must explore a second feature of potentially immediate Arctic changes in the near future, and the impacts on near-term evolution of methane emissions: namely, what the loss of the sea ice itself will do to atmospheric chemistry in the Arctic. Some research at NASA led by Apostolos Voulgarakis suggested that it could significantly alter atmospheric oxidation rates, which, following the standard work of Prather et al, would then be indistinguishable from having increased atmospheric concentrations of methane.

When one considers these two impacts, entailing both the source and sink side of the Arctic methane cycle, both intimately tied to the state of sea ice which is rapidly diminishing, plus the obvious likelihood for other rapid increases in chronic emissions (which have a 100% chance of increasing, the question being only when and how much) plus ever-increasing risks of abrupt releases as well, it should become apparent that Arctic methane emissions could suddenly increase considerably, even if it is true that methane hydrate emissions are not likely to respond immediately to the initial loss of sea ice cover.

Total potential anthropogenic methane reductions for near-term climate control are generally considered to be about 130 million tons per year, and the current Arctic methane emissions that could be enormously impacted immediately by upcoming ice losses are the ~8 million tons of ocean-wide sea surface production, as well as, perhaps somewhat more moderately, the ~8 million of shelf submarine permafrost talik and seep emissions (through enhanced vertical mixing, etc). Thus, these are already now ~12% as large as potential reductions, and since large-scale changes in regional hydrology, another immediate result from the sea ice loss, could also increase land-based Arctic wetland emissions considerably, it is not at all impossible for the near-term evolution of methane increases in the Arctic to equal a substantial portion of all potential anthropogenic methane reductions, which, in programs like the Global Methane Initiative, are currently scheduled to be cut over two decades or more.

It should become clear that James Hansen’s ‘Alernative Scenario,’ while still possible today, is at high risk of being lost as an effective path forward if we do not act soon. The best course of action is to initiate the most rapid possible cuts to those black carbon emissions most strongly impacting the Arctic, as well as ramping up methane reductions programs as quickly as possible, in the hopes that such negative impacts on the Arctic – which would also clearly lead to more rapid preconditioning of much more serious long-term problems (i.e., larger-scale methane hydrate destabilization) – could be forestalled as long as possible.

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