Recent Northern Hemisphere snow cover extent trends and implications for the snow-albedo feedback

Stephen J. Déry & Ross D. Brown

Abstract

Monotonic trend analysis of Northern Hemisphere snow cover extent (SCE) over the period 1972–2006 with the Mann-Kendall test reveals significant declines in SCE during spring over North America and Eurasia, with lesser declines during winter and some increases in fall SCE. The weekly mean trend attains −1.28, −0.78, and −0.48 × 106 km2 (35 years)−1 over the Northern Hemisphere, North America, and Eurasia, respectively. The standardized SCE time series vary and trend coherently over Eurasia and North America, with evidence of a poleward amplification of decreasing SCE trends during spring. Multiple linear regression analyses reveal a significant dependence of the retreat of the spring continental SCE on latitude and elevation. The poleward amplification is consistent with an enhanced snow-albedo feedback over northern latitudes that acts to reinforce an initial anomaly in the cryospheric system.

 

Oceanic gas hydrate instability and dissociation under climate change scenarios

Matthew T. ReaganGeorge J. Moridis

Abstract

Global oceanic deposits of methane gas hydrate (clathrate) have been implicated as the main culprit for a repeated, remarkably rapid sequence of global warming effects that occurred during the late Quaternary period. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, is poorly understood, and existing studies focus on deep hydrate deposits under equilibrium conditions. In this study, we simulate the dynamic response of several types of oceanic gas hydrate accumulations to temperature changes at the seafloor and assess the potential for methane release into the ecosystem. The results suggest that while many deep hydrate deposits are indeed stable under the influence of rapid seafloor temperature variations, shallow deposits, such as those found in arctic regions or in the Gulf of Mexico, can undergo rapid dissociation and produce significant carbon fluxes over a period of decades.

 

So, snow cover extent matches other measures of change; hardly a surprise, but a decent-looking summary of the period. Is there anything contentious in this paper? If not, it is another one to add to the ever-growing list of data supporting recent warming and confirming other observations. Does anyone know of a recent paper calculating the forcing from the albedo effect?

The clathrate ‘problem’ is a sticky one. I wish I could read the whole paper. This is pretty much what has been suggested for a while, that shallow deposits might be vulnerable, but I’d like to know what counts as a ‘rapid seafloor temperature variation’, both in amplitude and rate of change.

If the authors are correct, we have another reason to be concerned about the prospect of oil exploration in the Arctic, a prospect which must be very close, now, given the likelihood of continuing warming (well, in the case of the Arctic, it’s a relative term…). I note that Canada is building a large new deep water harbour in the far North, and also has a new military/observation base planned for Resolute. Goodness only knows what Mr. Putin has planned. It’ll also be interesting to see whether Barrow becomes a ‘boom town’, though after ‘30 days of night‘, some might take a bit of persuading.

 

As a side note, my apologies for relatively little activity recently;  sometimes, life just jumps up and bites you. Thanks to my regular readers and commenters for persisting with me during a ‘dull’ time.

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