Yesterday we talked about the big stuff–temperature rises, sea level rise, droughts, floods and storms. Today we’ll shift focus a bit and talk about ice.
There are three major accumulations of ice on Earth–Greenland, the Arctic Ocean and Antarctica. The National Snow and Ice Data Center is the go-to source for information about ice.
According to their 2015 Year in Review, “December ended with Arctic sea ice extent tracking between one and two standard deviations below average, as it did throughout the fall. This caps a year that saw the lowest sea ice maximum in February and the fourth lowest minimum in September. In Antarctica, December sea ice extent was slightly above average but far below the exceptionally large ice extents recorded for December 2013 and 2014. A slow-down in the rate of Antarctic sea ice growth in July was followed by near-average extents in the subsequent months.”
Arctic Sea Ice
For the ice covering the Arctic Ocean, it’s the mirror image of surface temperatures. Where global average air temperatures are bouncing on top of a plateau reached in 1998 (the pause which apparently is ending), Arctic ice levels are bouncing on top of a recently reached (and by no means permanent) floor. Both metrics have stabilized within a band of values, but nobody knows if they will stay there for any length of time.
“The record-low Arctic maximum occurred on February 25, 2015 and was among the earliest seasonal maxima in the 37-year satellite record. It was likely a result of very warm conditions in the Sea of Okhotsk and the Barents Sea (4 degrees Celsius or 7 degrees Fahrenheit above average), and low ice extent in the Bering Sea in March (when the maximum would more typically occur). The fourth lowest Arctic minimum occurred on September 11, 2015 and was likely a consequence of very warm conditions in July and an increasingly young and thin ice cover.”
Antarctic Sea Ice
The year will be remembered for a return to average levels for Antarctic sea ice extent after more than two years of record and near-record highs.
Again according to NSIDC, “From February 2013 through June 2015, Antarctic sea ice was at record or near-record daily extents. Antarctic sea ice set consecutive record winter maxima in 2012, 2013 and 2014. But during this year’s austral mid-winter period, Antarctic sea ice growth slowed. Since then, extent in the Southern Hemisphere has generally been slightly above average.”
The Antarctic Ice Sheet
The Antarctic Ice Sheet covers nearly 14 million square kilometers (5.4 million square miles), and is divided into three sections: the East Antarctic Ice Sheet, the West Antarctic Ice Sheet, and the Antarctic Peninsula. A recent paper by Zwally et al (a paper being vigorously challenged by scientists with activist leanings) says, “Mass changes of the Antarctic ice sheet impact sea-level rise as climate changes, but recent rates have been uncertain. Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82 ± 25 Gt a–1, reducing global sea-level rise by 0.23 mm a–1.”
“Parts of Antarctica are losing mass faster than before,” says Jay Zwally, a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a paper to appear in the Journal of Glaciology1. “But large parts have been gaining mass, and they’ve been doing that for a very long time.” According to Nature.com, “So much ice is piling up in the vast expanses of East Antarctica that, overall, it counterbalances the losses seen at glaciers thinning elsewhere on the frozen continent. It will take decades for Antarctic melting to overtake the mass gains and begin contributing substantially to sea-level rise.”
Essentially, the Western Ice Sheet, one of the smaller sheets, is losing ice quite rapidly. However the huge, huge Eastern Ice Sheet is gaining more ice than the WAIS is losing. For now.
The Greenland Ice Sheet covers roughly 1.7 million square kilometers (650,000 square miles).
Melt can occur at surprisingly high elevations on Greenland ice sheet. For example, observation stations operated by PROMICE regularly record melting at an altitude of 1,800m near Kangerlussuaq in western Greenland – even during cool summers.
2015 started off cold in Greenland but an unusually high melt occurred in July. SMB in the chart below refers to Surface Mass Balance:
Greenland is losing mass at about 250bn tonnes per year. That sounds like a lot, but it means that in the past decade, Greenland has lost less than 1% of its ice. We’re not going to lose the Greenland Ice Cap any time soon–scientists estimate that it would take 3000 years of global warming to lower the ice there by 50%.
However, as the Greenland ice sheet sits on land, meltwater that flows into the oceans will contribute to sea level rise. This is currently adding around 0.7mm a year to global sea levels, but if the ice loss continues from Greenland, this will likely increase through the 21st century.
Conclusion to Part 2
In the Arctic, sea ice minimums (and recently the maximums) decreased from 1979 to about 2008 and then stabilized roughly where they are now. Nobody really knows if it will stay at this ‘new normal’, return to previous highs or move on to even lower levels.
This obviously won’t affect sea level, but an ice free Arctic summer would undoubtedly have an impact on regional weather patterns. In addition it would contribute to global warming by having sun drunk in by open water as opposed to being reflected back into space by ice. If the more pessimistic scientists are correct, that could happen sometime within the next 30 years.
Really, not much of note is happening in either Greenland or Antarctica. When and if the Western Antarctic Ice Sheet finally collapses (as has been predicted for mechanical reasons since the 1920s–climate change is not involved except at the margins), we will all take notice. It will cause significant sea level rise. However, it hasn’t started yet and when it does start it is expected to take 25-50 years, giving us some time to prepare.
Both Greenland and Arctic ice are now being watched more carefully to see the impact of the soot coming out of China’s chimneys. It changes the albedo of the ice it lands on and hastens melting. Let’s send a Care Package of smokestack scrubbers to Beijing ASAP.