How does Arctic sea ice loss compare to Antarctic sea ice gain?
What the science says...
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Arctic sea ice loss is three times greater than Antarctic sea ice gain.
Have Arctic ice losses truly been balanced by Antarctic gains? The first point to clarify is that we are talking about floating sea ice, not to be confused with land ice. Land ice at both poles and in glaciers around the world is sliding into the ocean at an accelerating rate. This net loss of land ice is contributing to sea level rise.
However, Monckton is clearly referring to sea ice. The rapid decline of Arctic sea ice has indeed coincided with an increase in Antarctic sea ice. But do these two opposite trends cancel out as Monckton suggests? In reality, the upward Antarctic trend is only slight compared to the plummeting Arctic trend. Tamino has crunched the numbers and found the Arctic trend is in fact more than three times faster than the Antarctic one. The net result is a statistically significant global decrease of more than a million km2 or a few percent – would you agree with Monckton that this is “virtually no change”?
Figure 2: National Snow and Ice Data Center (NSIDC) Antarctic, Arctic, and global (sum of the two) sea ice extents with linear trends. The data is smoothed with a 12-month running average.
Sea ice area data shows the same thing as extent data.
Summer and Winter, Apples and Oranges
Monckton compares the Arctic summer to the Antarctic winter, not the most appropriate comparison. Sea ice grows and shrinks seasonally because polar latitudes have vastly more daylight hours in summer than in winter. When ice melts, it makes the surface less reflective and amplifies the warming (as is currently occurring in the Arctic), but this effect can only make a difference when the Sun is up. Thus the most important time of year for sea ice is its annual minimum which occurs at the end of the summer: September in the Arctic but February in the Antarctic.
So how do the two compare?
While the summer Arctic has lost an extent of about 2.5 million km2 (equivalent to the area of Western Australia), the summer Antarctic growth is only 0.3 million km2 (about the size of Victoria). Even that slight upward trend is less than the year-to-year variability; although 2003 and 2008 tied for the highest February extent, 2006 was third lowest. Again, the real world contradicts Monckton’s assertion that changes in the Arctic are being balanced out by the Antarctic.
The Third Dimension
Furthermore, Monckton fails to mention that Arctic sea ice is not only shrinking in extent but also has been thinning rapidly. Although its lowest extent was in 2007, its volume has continued declining since then, hitting another record low in 2010:
The volume data is supported by a sharp decline in thick multiyear ice (Figure 5).
Figure 5: NSIDC Arctic sea ice age from 1983 through 2011 (Source)
Meanwhile there has been a slight increase in Antarctic sea ice volume, but only by about 5,000 km3 (insufficient to offset the Arctic decline shown in Figure 4), and most of it in a few years at the start of the record.
The Polar Prognosis
As thinner and younger ice is easier to melt, the rapid Arctic melt is set to continue; ice-free summers are now probably inevitable. In contrast, the Antarctic increase is occurring despite the warming of the Southern Ocean and is expected to reverse as the warming continues. Antarctic sea ice is just a distraction from the accelerating losses from ice sheets and the looming specter of a sea-ice-free Arctic.
Last updated on 27 November 2011 by dana1981. View Archives