During the record hot year of 2016, both Arctic and Antarctic sea ice extents took a huge hit.
Extreme warmth in the Arctic helped to produce leading losses there. Values that began during January at 1 million square kilometers below average have steadily declined as the months progressed to near 2 million square kilometers below average. Meanwhile, the Antarctic — which began the year at near average sea ice extent values — saw significant losses as the region grew anomalously warm during austral spring. Today, sea ice extent values surrounding the Antarctic are now also just shy of 2 million square kilometers below average.
(Zachary Labe, one of the most well-recognized up and coming U.S. climate scientists, has produced this graph based on NSIDC recorded global, Arctic, and Antarctic sea ice values. As you can see, global sea ice extent during the hottest year on record has steadily plummeted to near 4 million square kilometers below average as the months progressed. Image source: Zack Labe’s Sea Ice Figures. Data source: NSIDC. You can also follow Zack’s informative twitter feed here.)
In total, global sea ice coverage is now about 3,865,000 square kilometers below average.
If you think that number sounds really big, it’s because it is. It represents a region of lost ice nearly 40 percent the size of the land and water area of the entire United States including Alaska and Hawaii. To visualize it another way, imagine all of the land area of Alaska, California, Texas, Montana, Arizona and New Mexico combined and you begin to get the gist.
Sea Ice Coverage — An Important, But Complex Climate Indicator
Many climate specialists have viewed sea ice as a kind of climate change canary in the coal mine. Sea ice sits upon the warming oceans and beneath a warming atmosphere. And these oceans are now taking up the majority of the heat being trapped in the atmosphere by fossil fuel emissions. Warming ocean surfaces have a higher specific heat value than the air and this greater overall energy capacity in warming regions generates a substantial blow to ice coverage even if the initial water surface temperature swing is only moderate.
Once sea ice is lost for a significant period, a kind of feedback loop comes into play where dark ocean surfaces trap more of the sun’s rays during polar summer than once-white ice coverage — which previously reflected radiation back toward space. This newly absorbed heat is then re-radiated back into the local atmosphere during polar fall and winter — creating an inertial barrier to ice reformation and ultimately generating a big jump in seasonal ocean and atmospheric surface temperatures.
(Highly pronounced ocean surface warming coupled with warm air invasions appears to be generating the extreme losses to sea ice now seen in the Arctic. The Barents Sea, shown above, has seen particularly extreme warming. Note the 11 C above average hot spot near the sea ice edge zone. In the Antarctic, the causes of losses remain uncertain. However, atmospheric warming and shifts in the circumpolar winds appear to be producing this effect even as slightly cooler than average surface waters remain in place — possibly due to storm related Southern Ocean upwelling and increasing fresh water outflows from Antarctic glaciers. Image source: Earth Nullschool.)
This dynamic is particularly pronounced in the Arctic where a thawing ocean surrounded by warming continents tends to readily collect heat even as atmospheric energy transfers from the south, in the form of warm wind events, have grown more pronounced. An effect related to the climate change influence known as Northern Hemisphere Polar Amplification.
In the Antarctic, the stormy Southern Ocean generates up-welling. This dynamic tends to cool the ocean surface even as it transfers heat into the deeper ocean. And increasing stormy conditions surrounding Antarctica related to climate change can intensify this effect. In addition, warm bottom waters melting sea-fronting glaciers in Antarctica produce a lens of fresh water which cools the surface and also traps heat below. So the signal coming from Antarctica with regards to sea ice has tended to be more mixed — with atmospheric warming and changes in wind patterns generating more variable sea ice impacts relative to the Arctic. So this year’s sea ice losses there are more difficult to directly link to climate change.
Zack Labe notes that:
The Arctic sea ice anomaly, however, fits with the ongoing Arctic amplification trend of thinning sea ice and loss of old ice. Additionally, it has been well noted in previous literature (i.e., http://onlinelibrary.wiley.com/doi/10.1029/2010GL044136/full …) concerning the increasing fall temperatures in the Arctic and possible causes.
Major Volume Losses From 2015 to 2016
Despite big losses to sea ice surrounding the Antarctic this fall, it is the Arctic where the damage and risk of further loss is most pronounced. Particularly, reductions to thicker, multi-year ice in the Arctic during 2015 to 2016 have been exceptionally severe:
In the above images, we see a comparison between late November sea ice coverage and thickness as provided by the U.S. Navy ARCc model. The left frame represents late November of 2015 and the right frame represents projected values for November 20, 2016. Note the greatly reduced coverage in the 2016 image. But even more noteworthy is the substantial loss of thicker ice in the Arctic Ocean north of the Canadian Archipelago and Greenland.
These two images tell a tale of a great loss of sea ice volume. One that the sea ice monitor PIOMAS confirms. According to PIOMAS, ice volume values during October were tracking near lowest levels ever recorded. And continued heat into November generates a concern that a period of new record low volume levels may be on the way.
But it’s not just the record low values that should be a concern. It’s the location of the remaining thick ice that’s a worry as well. For a substantial portion of the remaining thick ice is situated near the Fram Strait. Wind and ocean currents tend to push ice out of the Arctic Ocean and through the Fram. Ice tends to then be funneled down along the coast of Greenland and on into the North Atlantic where it melts. So the fact that a big chunk of the already greatly reduced remaining thick ice now sits on the edge of the sea ice version of Niagra Falls is not a good sign.
La Nina Years Tend to Push More Heat Toward the Poles
It is notoriously difficult to accurately forecast sea ice melt and refreeze trends in the various seasonal measures for any given individual year. And even many of the top sea ice experts have had a devil of a time forecasting the behavior of sea ice during recent years. However, one thing remains quite clear — the long term trend for sea ice in the Arctic is one of rapid decline.
(Arctic sea ice ‘Death Spiral’ by Andy Lee Robinson. Image source: Haveland.)
We are now entering a situation where one very warm winter followed by one warmer than normal summer could push Arctic sea ice values to near the zero mark. A situation that could effectively set off a blue ocean event in the near future. A number of prominent sea ice experts have predicted that it’s likely that such a state will be achieved rather soon — by the early 2030s under current trends. Others point toward nearer-term loss potentials. But there is practically no-one now saying, as was often stated during the early 2010s, that a blue ocean event could hold off until the early 2050s.
All that said, the trajectory going into 2017 for the Arctic at present doesn’t look very good. Both sea ice extent and volume are now at or well below the previous low marks for this time of year. Remaining thick ice positioned near the Fram Strait generates a physical disadvantage to the ice in general. In addition, NOAA has announced that La Nina conditions are now present in the Equatorial Pacific. And La Nina events tend to push more ocean and atmospheric heat toward the poles — particularly toward the Arctic.
Note: This article is written as a follow-on to the previous blog post — For The Arctic Ocean Above 80 North, It’s Still Summer in November — and they should be read together for context.
Disclaimer: I asked PhD student Zachary Labe to make a general comment on sea ice trends, to which he generously provided his particular take on the Arctic. I have also made my own best-shot science and observation-based analysis of the situation given current trends. Because of the fact that the present situation is new and evolving, some of my statements may well pass outside the bounds of currently accepted science. The fact that Labe commented in this post does not, in this case, mean that he agrees fully or in part with my particular initial rough analysis of the subject.
Hat tip to Andy Lee Robinson
Hat tip to Cate