Atop the world lies a thinning veil of ice. A gossamer lid covering a deep, dark Arctic Ocean. It is a reflector screen for incoming solar radiation during the months-long-day of Polar Summer. And a recent NASA study shows that this heat shield is starting to fail.
Ever since the late 1970s an Arctic warming at 2-3 times the rate of the rest of the globe has set off a 13.3 percent decline of sea ice at end summer during each and every following decade. And that cumulative loss is having an extraordinary impact. For the white, reflective ice cover by September has now, on average, fallen by nearly 50%. What remains is a thinner ice cover. One full of holes and interspersed with great and widening expanses of dark water.
Dark water and thinner, less contiguous, ice absorbs more of the sun’s heat. NASA notes that this added absorption can have far-flung impacts:
While sea ice is mostly white and reflects the sun’s rays, ocean water is dark and absorbs the sun’s energy at a higher rate. A decline in the region’s albedo – its reflectivity, in effect – has been a key concern among scientists since the summer Arctic sea ice cover began shrinking in recent decades. As more of the sun’s energy is absorbed by the climate system, it enhances ongoing warming in the region, which is more pronounced than anywhere else on the planet.
For years, polar scientists have been warning of signs this powerful amplifying feedback was speeding an already drastic warming for the Arctic environment. Now, a 15 year satellite survey conducted by NASA provides direct evidence that this is indeed the case — with the Arctic now absorbing 5% more incoming solar energy than it did in the year 2000.
(Click Image to Enlarge. Left frame shows summer sea ice fraction change with measures in dark blue showing a greater than 50% loss on average. Right frame shows changes in absorbed solar radiation with most of the Arctic showing a 5 watt per meter squared or greater increase in solar radiation absorption and sections of the Beaufort Sea peaking at 50 watts per meter squared additional solar radiation absorption. Image source: NASA.)
Averaged over the Arctic, the failing summer sea ice and newly revealed dark waters absorb an extra 10 watts per meter squared of solar heat radiation. That extra heat is equivalent to having a 10 watt light bulb burning on every square meter of the Arctic Ocean surface throughout the entire polar summer. Twenty four hours per day, seven days a week for the seasonal period.
In some regions, like the Beaufort Sea near Northern Canada and Alaska, the extra heat absorption is as much as 50 watts per meter squared greater than year 2000 levels. An extraordinary increase in Arctic Ocean heat uptake and, perhaps, one of the chief reasons why higher Latitude ocean surface temperatures have tended to range so high in recent years.
It’s a massive realignment of the Earth’s radiative balance and one that has occurred in only a relatively short period.
NASA scientists are quick to caution that to fully take into account climate variability, the study will need to continue for another 15 years. But when taking into account the massive 35 year drop off in sea ice since 1979, it appears likely that radiative balance changes are even greater than the 15 year NASA study indicates.
(NSIDC sea ice extent losses for Arctic since 1979 showing a 13.3% decadal rate of decline. Image source: NSIDC. Note NSIDC adds a linear trend line. However, historic rates likely show a more rapidly down curving melt progression — see image below.)
Overall, this loss of sea ice and related increased heat absorption has pushed melt season onset times a full week sooner than 1982 onsets 32 years ago. Earlier melt season starts lead to more heat absorption — a classic feedback cycle also recognized in the new NASA report.
In addition, the report links added Arctic Ocean summer heat absorption to loss of older, thicker ice observed throughout the Arctic region. Since 2000, more than 1.4 million square kilometers of 3 meter or thicker ice has melted out of the Arctic Ocean system. That ice has been replaced by coverages of less than 2 meters in thickness — another aspect of amplifying warming feedbacks at play in the Arctic.
Walt Meier, a sea ice scientist at NASA Goddard Space Flight Center in Greenbelt Maryland, notes:
Having younger and thus thinner ice during winter makes the system more vulnerable to ice loss during the summer melt season.
Whether these amplifying feedbacks will result in ice free summer conditions sooner rather than later is still a matter of some discussion among scientists. Following the 13.3 percent per decade trend puts us at ice free summers sometime around 2030-2035. But the large swings in annual variability could result in an earlier year in which ice free conditions occur. In addition, some scientists assert that amplifying heat feedbacks in the Arctic are enough to result in ice free summers as soon as 2017 to 2020.
To this point it may be worth considering that the 13.3 percent per decade rate may be steepening as is hinted at in the below long term graph:
(Long term melt trend compiled by Larry Hamilton. Image source: Here.)
Regardless of timing, the historic loss of Arctic sea ice is already resulting in dramatic impacts to the Earth’s radiative balance and to the distribution of global surface heat absorption. A circumstance that a number of studies have implicated in changing Jet Stream patterns and enhanced meridional (north to south and south to north) air flows.
Links:
Satellites Measure Increase of Sun’s Energy Absorbed in the Arctic
Hat tip to TodaysGuestIs
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