Thursday, 20 July 2017

Sea Ice Coverage Has Fallen Off a Cliff

Global Sea Ice Coverage Has Fallen Off a Cliff — Impacts Likely to Be Wide-Ranging

19 July, 217


Frozen water.
It’s an important aspect of our world. One that is essential to maintaining a stable climate and, by extension, the health of modern civilizations. Today, due to a continued warming of the globe, every form of frozen water — be it frozen water locked in glaciers, snow, or sea ice — is under threat. And we are almost daily reminded of new losses coming from these needed collections of cold.
Recently, however, one of these subsets of global ice has taken a very serious blow. For this past year, as ocean and land surfaces warmed to above 1 C warmer than late 19th Century averages, has seen a precipitous fall in the coverage of global sea ice. And we are now in uncharted territory as the Earth’s sea ice extent, area, and volume have fallen to never before seen lows.

(Sea ice area [upper right], extent [upper left], and volume [lower graphs] have all seen very serious declines that have now lasted for a full year. Since reflective sea ice is an important regulator of global and regional climates, the impacts of such a considerable loss is likely to be both long-term and wide-ranging. Image source: Global Sea Ice.)

Total sea ice area and extent have now ranged between 2 and 3 million square kilometers below the 38 year average for about a year now. That’s a region of sea ice larger than Greenland which has been removed from the face of the Earth now for the better part of four seasons. Global sea ice volume losses are now in the range of 12,000 cubic kilometers — each cubic kilometer roughly equal to a moderate-sized mountain. These are very considerable losses. 

But perhaps more ominous than the losses themselves is the fact that they seem to be sticking around — locking in a permanent warming-related-change to the Earth System, its weather and environment.

To be clear, there are some things that sea ice loss does not directly impact. And the first of which is sea level rise. Because sea ice already floats on the surface of the ocean and because it already displaces water, melting sea ice does little to change the level of the ocean surface directly.
(A very informative video describing ice albedo feedback. We do not, however, support some of the video’s sponsors who, unfortunately, appear to be ubiquitous.)

That said, there are many things that sea ice loss does affect. And the first is global temperature balance. Sea ice serves as both a reflective shield that throws back the sun’s heat during summer and as an insulator that locks warmer ocean waters below during winter. 
Remove a significant portion of the global sea ice, as we have done, and you’ll end up with oceans that both draw in more heat during the warmer months and bleed out more stored ocean heat into the atmosphere during the winter.
Such heat will be both stored and delivered exactly where it can do the most harm — in the polar regions. And, as a result, recently ice-liberated oceans will warm more rapidly in areas that are directly adjacent or close to the very large glaciers covering Greenland and Antarctica. As such, though melting sea ice has no direct, immediate impact on sea level rise, it can create an added pressure for the loss of land-bound and sea-fronting glaciers that will raise ocean levels if they melt.
(Arctic sea ice loss feedbacks produce complex and far-reaching impacts to the entire Arctic system. Image source: National Science Foundation.)

Arctic regions also face considerable added heat pressure to permafrost, boreal forests, and other carbon stores as a result of Arctic Ocean albedo feedbacks due to sea ice loss. In addition, warm pools of ocean water in the far north will aid in further destabilizing already-altered weather patterns. So sea ice loss is likely to continue to result in a worsening of the Jet Stream excursions that have already contributed to extreme weather — particularly in the Northern Hemisphere.

But perhaps the most concerning impact of sea ice loss is an alteration to seasonal temperature exchange. More heat absorbed by oceans during summer and then ventilated back to the atmosphere during fall and winter will tend to result in a lag in global cooling into the fall season even as winter will tend to warm.

(A roll-back of sea ice results in much warmer temperatures over nearby permafrost zones. This week, 81.5 F [27.5 C] temperatures are predicted for parts of the Yamal Peninsula — a region that has recently drawn attention for its newly discovered methane blow-holes. Image source: Earth Nullschool.)

Such a lag enhanced by sea ice loss is arguably already in play in the Northern Hemisphere — where increasing rates of heat exchange between the tropics and middle latitudes and the pole have already been observed. However, if Southern Hemisphere sea ice remains reduced, a similar heat exchange and polar amplification pattern is likely to begin setting up there as well.
The upshot is that the observed considerable loss of global sea ice coverage is likely to produce harmful or disruptive feedbacks in the Earth’s climate system in the near term. Stresses to the other frozen systems of the world will tend to increase as a result. Extreme weather events are at risk of worsening. Rates of polar warming could escalate. And disruptions to traditional seasonality will tend to become more apparent.


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