Overall, worldwide sea ice totals have been declining over the past few decades. This trend has been led by a massive summer collapse of sea ice in the Arctic. But, on the other side of the world, in Antarctica, sea ice area and extent have been slowly expanding. This seeming contradiction recently spurred researchers to take a closer look at Antarctica to determine why sea ice would be expanding even though worldwide atmospheric and ocean temperatures are on the rise.
What they found was an amazing and complex combination of forces driving a moderate sea ice expansion in the southern hemisphere. Warmer waters coming into contact with submerged glaciers slowly melts the ice. In addition, a warming Antarctic continent disgorges large volumes of water each year. This fresh melt water, flushing into the ocean at a rate of 250 gigatons each year, then expands, covering the ocean surface in a thin layer surrounding Antarctica. Not only does this fresher water freeze at higher temperatures, it keeps warmer waters from rising up to melt the sea ice from below. The result is that sea ice is both insulated and made of fresher water. So until atmospheric and ocean temperatures rise enough to overwhelm this dynamic, Antarctic sea ice will remain protected by insulating processes coming from melting glaciers.
Warmer water trapped in the ocean depths surrounding Antarctica has also played a role in heating the world’s deep oceans. This heating was recently detected in a new study conducted by Kevin Trenberth and colleagues. The study found that a significant portion of the last decade’s heating had been sequestered in the deep ocean. Now it’s apparent that glacial melt in Antarctica may have played a role.
The Arctic sea ice, thus far, hasn’t benefited from a similar insulating process. The result was an 80 percent sea ice volume loss since 1979 and a high risk that sea ice will completely melt one summer between now and 2020. It’s possible that Greenland melt may continue to increase, freshening the Arctic’s waters, and providing a similar benefit at the cost of enhanced sea level rise and more extreme weather. But ocean currents, geography, and salinity dynamics for the Arctic are different from that of the Antarctic. So it is uncertain if melt will play as large a role in insulating northern hemisphere sea ice as it has in the southern hemisphere.
It is worth noting that rapid glacial melt, though it drives more extreme weather events even as it more rapidly increases sea level, tends to put a powerful damper on global temperature increases once glacial melt reaches the 1 meter mark. The heat energy goes more into melting the ice and less into warming the atmosphere and oceans. The negative feedback of fresher ocean waters in the polar regions as well as iceburgs floating in rapid glacial melt zones also has a net cooling effect. The result is that a degree or more of global temperature increases may be ‘held in check’ as the ice melts. Rapid ice melt decades may result in brief periods of relative cooling (where temperature increases back off from 1.5 or 2 degrees above average to around .9 to 1.3 degrees above average).
It’s a balancing effect and trade-off where you end up with more changes to the Earth’s environment and less overall heating in the short-term. This delayed heating effect of ice melt should not be seen as a good sign, however. As mentioned above, it comes at the severe cost of increased weather extremes and more rapid ocean level increases. In the end, once the messy transition decades are passed, a more liquid ocean results in more water vapor in the atmosphere, warmer Arctic and Antarctic environments that pump more greenhouse gasses into the atmosphere, receding glaciers and snow cover reducing the Earth’s reflectivity and adding further warming, and a warmer deep ocean resulting in more ocean methane release.
To get an idea how Greenland and Antarctic melt might dramatically impact world weather while putting a short-term dampening on global warming over the coming decades, take a look at this paper by James Hansen:
It is worth noting that the scenarios examined in the paper come as a result of a relatively moderate increase in human greenhouse gas emissions: the A1B scenario. However, current emissions have increased more along the A1FI scenario which would likely result in even more climate volatility than the Hansen paper suggests.
The thing to take away from this new study is that both the Arctic sea ice collapse and the slower expansion of Antarctic sea ice are caused by the same forcing — human caused global warming — and that the glacial melt now resulting in localized cooling is also driving enhanced sea level rise and more extreme weather.
Please find more information on these new, ground-breaking studies here: