August 2012

Arctic Sea Ice:  Why It Matters

On August 26, satellite data analyzed by the U.S. National Snow and Ice Data Center (NSIDC), as well as similar estimates from Norway’s Polar Institute, made it official:  the 2007 record low for summer Arctic sea ice was officially broken, and with nearly an entire month of melting left before the sun sets.

For those of us who follow this annual drama, checking the NSDIC website almost obsessively, yet used to waiting until the very last days of melt before we know the final verdict: the rapid fall of the past two months was a shock.  Yes, we expected this to happen again, just as we expect someday to see that line reach zero.  But I am aware of no ice scientist who expected the record broken like this.

This is news much more for the entire globe, rather than the relatively few cryosphere scientists, policy makers and NGOs.  Why?   Because less sea ice is bad for the stability of the climate on the entire planet.  Here in other words find a few quick explanations as to why the rest of the world should care about that downward line on the NSIDC graph:

– Less sea ice means a darker surface (water) in a place where the sun shines close to 24 hours a day, even this close to the equinox.  Darker surfaces absorb more heat.  This makes the Arctic warmer, and makes even more ice melt, which leads to even more melting, and more warming.

– This greater heat in the Arctic Ocean leads to greater melt of snow and ice on nearby landmasses such as Greenland.  That in turn exposes more dark rock, which also speeds Arctic warming, same as the sea ice.

– Greater melt on land leads to greater sea level rise globally, unlike sea ice melt (think ice cubes in a glass of water).

– Greater warming in the Arctic also leads to more permafrost (on land) and frozen seabed (offshore) melt, which means a higher release of methane and CO2.  Release of these two powerful greenhouse gases speeds global warming further – in methane’s case, quite a bit in the near-term (over the next 10-20 years), leading to – you guessed it – even more warming in the Arctic as well as elsewhere — and from CO2, over centuries.

– A warmer Arctic means a warmer globe simply from what scientists term “heat transport:” if you have a house with a hot attic, the entire house eventually becomes hotter.  The Arctic has served as a “cold attic” for the rest of the globe, a kind of global air conditioning.  As it warms, the nearby regions have less cooling benefit from the Arctic, and the entire globe warms more.

– Most scientists also believe that a warming and melting Arctic leads to greater storminess in the Arctic and nearby regions of the northern hemisphere, as the atmosphere becomes warmer, more humid and less stable.  Certainly this summer In the U.S. northeast, the number and intensity of violent storms seems greater than normal, though the data remain to be analyzed.

Finally, we can take a big-picture, geologic look at the “why should we care” issue:  there is no human record of this little summer sea ice.  It is possible that about 5,500 years ago, or more likely during the Holocene Thermal Maximum 8000 years ago, summer sea ice was at low levels perhaps comparable to today, if not entirely free of summertime sea ice.

However, the only time we can be reliably certain that the Arctic was ice-free in the summer was 125,000 years ago, during the height of the last major interglacial period. That should be the real reason why Arctic sea ice matters to the human condition, because sea level was 4 to 6 meters (13 to 20 feet) higher than it is today, due to partial melting of Greenland and even Antarctic ice
sheets.  Indeed, global averaged temperatures today are getting close to the maximum warmth seen during that last inter-glacial – and CO2 levels today already are higher than they were then, meaning greater warming is already built into the climate system.

Those are more than enough reasons for the whole globe to care about the squiggle of lines moving persistently downward on the NSIDC website (http://nsidc.org/arcticseaicenews/). We should all of us be watching in the weeks, and years, to come.

Pam Pearson

 

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