Greenland is melting that quickly.....

A REBUTTAL OF "THE GREENLAND-ANTARCTICA MELTING PROBLEM DOES NOT EXIST" ASSERTION BY C. OLLIER, CCNet 1.11.07

Andrew Glikson and Barry Brook [geospec@iinet.net.au]

Dear Benny

 

We refer to C. Ollier's assertion "The Greenland-Antarctica melting problem does not exist" (CCNet 1.11.07).

 

We would have been delighted to concur, were it not for the already large and rapidly growing body of empirical and direct observational evidence for accelerated melting of the Greenland and west Antarctic ice sheets, occurring now.

 

Ollier states: "Hansen is a modeller and his and his scenario for the collapse of the ice sheets is based on a false model. Hansen has a model of an ice sheet sliding along an inclined plane, lubricated by meltwater, which is itself increasing because of global warming."

 

First, Hansen et al.'s papers are based on direct observations, both of current atmospheric changes and glacial/interglacial records (see J. Hansen et al., Roy. Soc. London, 16 January, 2007; J. Hansen et al., Proc. Natl. Acad. Sci. 101,16109, doi10.1073/pnas.0406982101 (2006); J. Hansen et al., Science 308, 1431, 2005). The advantage of using past information of ice sheet dynamics is that, whilst no certainty exists that models realistically represent all relevant processes, observed geophysical responses to climate change during the glacial-interglacial cycles provide a fundamental basis for calibration of current climate change.

Second, Ollier takes little account of recent glaciological studies in Greenland, which indicate internal ice sheet fracture (mullion) dominated dynamics (Bamber et al., 2007, 'Rapid response of modern day ice sheets to external forcing' Earth and Planetary Science Letters, Vol 257, p 1-3). The internal collapse of ice sheets, coupled with outflow glaciers, which surround both Greenland and west Antarctica, and the reduced albedo caused by vast pools of surface melt water result in accelerated loss (see Steffen K., Huff R., 2002. A record maximum melt extent on the Greenland ice sheet in 2002. Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder, CO 80309-0216)] and Steffen K., Nghiem S.V. Huff, R. and Neumann G. 2004. The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations. Geophysical Research Letters, 31 (20), L2040210. 1029/2004GL020444).

Satellite gravity and microwave measurements indicate a doubling of Greenland ice melt areas per decade (NASA 2006; Greenland ice loss doubles in past decade, raising sea level faster, news release, 16 Feb. http ://earthobservatory.nasa.gov/Newsroom/ Nasa News/2006/2006 021621 775.html). Rates of ice loss of the Greenland ice sheet have increased, involving an increase in spring melt area of 16% from 1979 to 2002. Satellite scanning of the Antarctic ice sheet during the period from April 2002 to August 2005 found that it's mass decreased at a rate of 152±80 cubic km per year. Most of this mass loss came from the West Antarctic Ice Sheet. GRACE-based estimates identify ice loss of 77±14 km3/year in the West Antarctic and a gain of 80±16 km3/year in Enderby Land in the East Antarctic.

Due to sparse distribution of measurement stations in Antarctica, the balance between ice melt and snow fall is not clear. However, a recent review of this topic in Science (Shepherd & Wingham 2007, 315, 1529-1532 DOI: 10.1126/science.1136776) concluded: "...much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade. In both continents, there are suspected triggers for the accelerated ice discharge-surface and ocean warming, respectively-and, over the course of the 21st century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models."

 

The IPCC 2007 documents a near doubling of sea level rise from 0.18±0.05 cm/year in 1961-2003 to 0.31±0.07 cm/year in 1993-2003, and combined melting of Greenland and Antarctic ice sheets of 0.019 cm/year to 0.041 cm/year. The IPCC states: "The remainder of the ice loss from Greenland has occurred because losses due to melting have exceeded accumulation due to snowfall."

 

Ollier states: "The very ice cores that are used to determine climates over the past 400,000 years also show that the ice sheet has grown over that period by accumulation of stratigraphic layers of snow, and has not been deformed or remelted." We wonder how does Ollier reconciles this statement with the fact that the ice core record of Greenland goes only to the last interglacial? (Willerslev et al. 2007, Science 317, 111-114, DOI: 10.1126/science.1141758).

Ollier refers to the Vostok and EPICA ice cores from internal and marginal parts of East Antarctica as "evidence" no significant melting occurred during the interglacials. However, the point is irrelevant. The East Antarctic ice sheet is believed to be comparatively stable, whereas concern hinges on rapid melting of the West Antarctic, where the base of the ice sheet lies beneath sea level, and on Greenland, where accelerated melting is taking place across large parts of the ice sheet.

 

An accelerated melting of continental ice sheets is hardly surprising, given the extreme reduction in Arctic sea ice extent from 5.6 million square km in September 2005 to 4.13 million square km in September, 2007 - namely MORE THAN 10 PERCENT IN 2 YEARS (http://nsidc.org/ accessed October, 2007).

 

In the article "The Big Melt" (http://www.carbonequity.info/docs/arctic.html), D. Spratt summarizes the current climate change scenario in the following terms:

(1) Climate change impacts are happening at lower temperature increases and more quickly than projected by the IPCC;

(2) the Arctic's floating sea ice is headed towards rapid summer disintegration as early as 2013, a century ahead of the IPCC projections;

(3) The rapid loss of Arctic sea ice will hasten the disintegration of the Greenland ice sheet, and a rise in sea levels by even as much as 5 metres by the turn of this century is possible.

 

Given the accelerated increase in the level of greenhouse gases, mean global temperatures (particularly at high latitudes, where temperatures have increased at three times the global average), the current reduction of the Arctic sea ice (22% over the last 2 years), pole-ward migration of climate zones and weather systems, as is affecting southern Australia, and the role of anthropogenic emissions (some 300 billion tons carbon since the industrial revolution), the spectre of rapid meter-scale sea level rise (Rahmstorf 2007, Science 315, 368) is a major source of concern.

It is the current unprecedented observations, and accelerating trends - not the modelled projections - which now speak clearly on the scope and urgency of this problem.

 

Andrew Glikson, Australian National University

Barry Brook, University of Adelaide