Guest post by David Middleton
The thaw is happening far faster than once expected. Over the past three decades the area of sea ice in the Arctic has fallen by more than half and its volume has plummeted by three-quarters (see map). SWIPA estimates that the Arctic will be free of sea ice in the summer by 2040. Scientists previously suggested this would not occur until 2070. The thickness of ice in the central Arctic ocean declined by 65% between 1975 and 2012; record lows in the maximum extent of Arctic sea ice occurred in March.
The most worrying changes are happening in Greenland, which lost an average of 375bn tonnes of ice per year between 2011 and 2014—almost twice the rate at which it disappeared between 2003 and 2008 (see chart). This is the equivalent of over 400 massive icebergs measuring 1km on each side disappearing each year. The shrinkage is all the more perturbing because its dynamics are not well understood. Working out what is going on in, around and underneath a supposedly frigid ice sheet is crucial to understanding how it will respond to further warming and the implications of its demise for rising global sea levels (see article).
375 billion tonnes per year… Oh my!
400 massive icebergs measuring 1km on each side disappearing each year… Oh no!!!
Wait a second… Those sound like big numbers… But how big are they compared to the Greenland ice sheet?
The USGS says that the volume of the Greenland ice sheet was 2,600,000 km3 at the beginning of the 21st century.
According to the “ice sheet goeth” graph, since 2001, Greenland lost about 3,600 gigatonnes of ice or about 3,840 km3 … That equates to a 16 km x 16 km x 16 km cube of ice (3√ 3,840 = 15.66). That’s YUGE! Right? Not really.
It’s not even a tiny nick when spread out over roughly 1.7 million square kilometers of ice surface. That works out a sheet of ice less about 2 meters thick… Not even a rounding error compared to the average thickness of the Greenland ice sheet.
- 2,600,000 km3 / 1,700,000 km2 = 1.53 km
The average thickness of the Greenland ice sheet is approximately 1.5 km (1,500 meters). 2 meters is about 0.15% of 1,500 meters.The thickness of the Greenland ice sheet is truly apparent on this radar cross section:
From a thickness perspective, 2 meters looks like this:
Using The Economist ratio of 400 km3 to 375 gigatonnes, 2,600,000 km3 works out to 2,437,500 gigatonnes. When some actual perspective is applied, it is obvious that “the ice sheet goeth” nowhere:
Despite all of the warming since the end of Neoglaciation, the Greenland ice sheet still retains more than 99% of its 1900 AD ice mass.
Multiple Choice Quiz
Fill in the blank:
Alarmists are _________ perspective.
- a) allergic to
- b) ignorant of
- c) willfully ignoring