Agreement polar ice sheets are melting

By Ken Perrott 02/12/2012

Many climate scientists felt the conclusions on effects of global warming in the 2007 IPCC review were too conservative. One reason was the estimation of likely melting of ice sheets and its effects.

Problem was that there was insufficient knowledge to draw definite conclusions. And the measurements of changes in ice sheets just wasn’t accurate enough.

That’s now changed and a large number of experts agree global warming has caused loss of ice from these ice sheets. And this has contributed to measured increases in sea level.

Richard A. Kerr reports in Science (see Experts Agree Global Warming Is Melting the World Rapidly):

“Forty-seven glaciologists have arrived at a community consensus over all the data on what the past century’s warming has done to the great ice sheets: a current annual loss of 344 billion tons of glacial ice, accounting for 20% of current sea level rise. Greenland’s share—about 263 billion tons—is roughly what most researchers expected, but Antarctica’s represents the first agreement on a rate that had ranged from a far larger loss to an actual gain. The new analysis, published on page 1183 of this week’s issue of Science, also makes it clear that losses from Greenland and West Antarctica have been accelerating, showing that some ice sheets are disconcertingly sensitive to warming.”

He’s referring to the major paper by Andrew Shepperd and others, A Reconciled Estimate of Ice-Sheet Mass Balance.

Over recent years climate change deniers/contrarians/sceptics have cherry picked data to counter any suggestion that the earth’s large ice sheets are melting. They have pointed to increased amounts of ice in Eastern Antarctica to balance reports of massive losses of ice in the Arctic. (Have a look at this animation to see how such data can be cherry picked). Similarly they have tried to hide concern of the loss of land ice by stressing reports of local increases in sea ice.

But the paper by Shepperd et al. combined data from satellite altimetry, interferometry, and gravimetry measurements. This provides more reliable estimates of changes in the ice sheets, and gives some detail of these changes. This figure from the paper gives an idea of the detail of their findings. It shows that all the major regions of the polar ice sheets except one (East Antarctica) have lost mass since 1992. The authors also estimate that mass loss from the polar ice sheets has contributed roughly 20 percent of the total global sea level rise during that period (at a rate of 0.59 ± 0.20 millimeter year−1 ).

Figure S1 from Shepperd et al.: Cumulative ice mass change of West Antarctica ((WAIS) East Antarctica (EAIS), Greenland (GrIS), and the Antarctic Peninsula (APIS).

And to underline the fact that denier claims of amounts of ice increasing in Antarctica are false, NASA recently displayed this figure showing data from Antarctica from their satellite measurements

Monthly changes in Antarctic ice mass, in gigatones, as measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 to 2011. Image credit: NASA-JPL/Caltech; NASA GSFC; CU-Boulder; Technical University of Munich; Technical University of Denmark; Delft University of Technology, Aerospace Engineering, Netherlands; Durham University, UK; Leeds University, UK

Could those climate change deniers/contrarians/sceptics please stop hiding behind claims that gains by Antarctic ice sheets balance losses from ice sheets in Greenland and the Arctic.

They don’t.

See also:
Science: Major Regions of Polar Ice Have Been Shrinking Since 1992
Polar Ice Sheets Losing Mass, Several Methods Show
New Study Shows Global Warming Is Rapidly Melting Ice at Both Poles
Human-Caused Climate Change Signal Emerges from the Noise
Study: Polar ice sheets in Antarctica, Greenland melting 3 times faster than in ’90s
Ice Sheet Loss at Both Poles Increasing, Study Finds
Projections of sea level rise are vast underestimates
“Hard” “Authoritative” Evidence Of Climate Change Begins To Overwhelm Even Fox

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0 Responses to “Agreement polar ice sheets are melting”

  • Agreed that some polar ice sheets are melting but this is actually trivial. What is important is which ones and what is causing it. Right off the bat, I must tell you that there is no global warming today and there has not been any for sixteen years. Hence, they are not melting because of any global warming. In the Antarctic only the West Antarctic Ice Sheet (WAIS) shows significant warming thanks to its geographic circumstance. It sits upon an archipelago and its ice cliffs drop directly into the ocean on three sides of it. Hence, it is open to the vagaries of ocean currents and has been subject to periodic collapses since the Pleistocene. These are recorded in sediments of the Ross Sea. A large amount of melt-water cascaded into the Ross Sea 18,000 years ago, again 10,500 years ago, again 5,000 years ago and then again 1,500 years ago. At the present time the ice facing the Amundsen Sea is being undermined by warm water rising up from below as prevailing winds blow away the cold surface water. It would not surprise me much if this will lead up to another potential collapse. But the large East Antarctic ice mass is not melting at all but even gained a little mass from snowfall. The story with the Arctic is entirely different. Although there is no global warming today the Arctic is an exception to the rule. Arctic warming started suddenly at the turn of the twentieth century, after two thousand years of slow, linear cooling. It paused in mid-century from 1940 to 1970, then resumed, and is still going strong. There was no concurrent increase of atmospheric carbon dioxide when it started and this rules out the greenhouse effect as a cause of warming. That is because the absorbance of carbon dioxide in the infrared is a property of the gas and cannot be changed. If you want it to do more warming you must put more gas in the air and this did not happen. It is likely that the cause of this warming is a rearrangement of the North Atlantic current system at the turn of the century that started to bring warm Gulf Stream water into the Arctic ocean. There are numerous observations of warming and currents entering the Arctic in the twenties and thirties. Recent warming has been directly measured by oceanographic observations, and climate history based on foraminiferal cores and Arctic lake deposits has been determined. The mid-century pause in warming can be easily understood if the previous configuration of currents temporarily returned. Such abrupt changes are impossible for any greenhouse warming to execute. The actual warming has been several times faster than global warming theory based on the greenhouse effect has predicted. This shows itself most noticeably in the reduction of sea ice cover over the years. IPCC AR4 report, for instance, grossly underestimated the rate of Arctic sea ice loss within the last 30 years. It is clear that their predictions about the Arctic simply cannot be trusted. And that goes for their other warming predictions too. In 2007 they thought that warming in the twenty-first century will proceed at the rate of 0.2 degrees per decade. So far, there has been none and there is no reason to think that this will change anytime soon.

    • Arno – this sounds like a current denial mantra “I must tell you that there is no global warming today and there has not been any for sixteen years.”

      Climate change is a trend picked up only over several decades. That’s required to extract any trend from the noise.

      Consequently the denier trick of finding statistically non-significant changes over 10 years or so is pretty obvious. “Hide the increase” I think they call it.

      And its ludicrous to make judgements of IPCC projections for this century by considering only 10 years and ingnoring the details of the scenarios the IPCC used for the different projections.

      As for the land-based ice sheets – these have decreased for the Antarctic Peninsula, West Antarctica and Greenland.

      Perhaps you should go back and read the post. I mentioned the conservative position of AR4 and why. It’s not a matter of trust – its a matter of the lack of reasonable data at the time for that review. Hence the large uncertainty. It is studies like this which will enable a better estimate of the effects of climate change and we should notice such assessments firming up in the next review.

      I think you are straw-clutching when you claim the pattern of global temnoperatures from 1940-1970 “rules out the greenhouse effect as a cause of warming.” It doesn’t – global temperatures were, and are, a complex result of several natural and man-made effects. We can understand the changes during that period by considering all the effects together, including greenhouse gases and particulates derived from human activity.