DeConto and Pollard – An Antarctic Science (Fiction?) Disaster

Readers may recall the announcement of the PR for the recent paper claiming Sea-Level rise from Antarctic ice sheet could double in WUWT. In a tongue and cheek way, I prefaced it with “Oh Noes!” due to the ridiculous claims being made from model output. I wasn’t the only one seeing this paper as flawed. It’s actually worse than we thought.

Guest essay by Patrick J. Michaels and  Paul C. “Chip” Knappenberger, Center for the Study of Science, Cato Institute

There’s one thing that climate scientists of all stripes and flavors agree would be an unmitigated disaster: A sudden and dramatic melting of land ice, raising sea levels ten feet or so in a century.

Three years ago, it appeared that this monster had been put to bed by Denmark’s Dorthe Dahl-Jensen, when her team drilled all the way down through the ice to Greenland’s bedrock, providing the first reliable data from there concerning the warmest period in recent geological history, known as the Eemian. She found that for six thousand years (roughly from 122,000 to 128,000 years ago) summer temperatures in Northwest Greenland, where her ice core was extracted, averaged a whopping 11°F warmer than the 20^th century average.

Remarkably, she estimated that Greenland only lost 30 per cent of its ice after six millennia. The integrated heat added to the ice over that span was roughly twenty times as much heat as humans could unload on it from greenhouse gases in 500 years, so the Greenland-driven apocalypse just isn’t going to happen.

Dahl-Jensen did note a curious mystery her work had uncovered. It’s well-known, from a number of independent sources, that Eemian sea levels were around twenty feet higher than the current era. Her ice-loss data suggested Greenland could only raise sea levels about one-third of that. The rest of the water had to come from the only other possible source, Antarctica.

The notion of an alarming rise in the ocean coming from there anytime soon has always been difficult to entertain. It is really cold down there and any melting should take a very long time—thousands of years—to do very much.

That just changed. Or at least it just changed in a complex and touchy simulation by Robert DeConto (University of Massachusetts) and David Pollard (Penn State) that made it above-the-fold on the front page of the March 31 New York Times. It seems that they shrunk the time for Antarctica to raise sea levels over ten feet a century from roughly the 50^th century, to the 22^nd (!).

Before the world gets all On The Beach-y about this, maybe there are devils hiding in the paper’s details. Indeed, there’s a forest of horns hidden in the dense but precise prose published in Nature.

For every predicted climate disaster, there has to be some type of climate model to project future temperatures. The authors used two (one for the ocean and the other for land). The first is a commonly employed general circulation model (GCM) from the National Center for Atmospheric Research in Boulder. The second is a less-common, smaller-scale “Regional Climate Model” (RCM) applied over the continent. These were then input into models of ice dynamics, including a new one that took rainfall (it really doesn’t rain in Antarctica now) and sloshed it into the continent’s huge glaciers, creating gigantic crevasses that crack truly ginormous hunks of ice off into the ocean. The new ice dynamics model is extremely sensitive to the settings of its large variety of handles and knobs—the settings of which can only be guessed at as the physics that the model is built upon is not well developed.

And a predicted disaster is only as reliable as the models that go into it.

The ice dynamics model is in its infancy, and the climate models used to generate temperatures around Antarctica are hot. Way too hot.

According to Andrew Monaghan (Ohio State), writing in Geophysical Research Letters: “20th century (1880–1999) annual Antarctic near-surface air temperature trends in the GCMs are about 2.5-to-5 times larger-than-observed.” Monaghan added this warming: “Until these issues are resolved, IPCC projections for 21st century Antarctic temperature should be regarded with caution.” We’re not sure the press got that memo.

Buried near the bottom of the supplementary material supplied to Nature, we can see that the climate model overproduction of warming infects the DeConto and Pollard paper as well. According to the authors, large areas of the continent (not just the well-known warming of the tiny Antarctic Peninsula that points towards South America) should have warmed some 7-15°F by now (Figure 1, left).

They didn’t. According to Ryan O’Donnell and others writing in the Journal of Climate in 2010, summer temperatures have risen since reliable records begin with the 1957 International Geophysical Year, but only about 5-10 per cent of what the RCM says should have been happening in many spots (Figure 1, right).

Figure 1. (left) Total temperature change between pre-industrial condition and the present produced by the DeConto and Pollard climate model; (right) observed trend (˚C/decade) in temperature from 1957-2006 determined by O’Donnell and colleagues (2011). Multiple the latter by five to get an idea of the total temperature change since 1957.

A good climate disaster also requires some guesstimates of how much carbon dioxide is going to increase in the future. The juiciest ones in the new paper assume atmospheric concentrations that even the United Nations’ has acknowledged as substantial outliers. And the paper lets it increase to eight times over the 19^th century background, something no one we know has ever entertained as a basis for future climate scenarios. (We’re currently around four-tenths of the way to a doubling.)

There’s also a scenario where the increase in carbon dioxide is slower and more realistic, and—you guessed it—the end of the world is delayed by several centuries.

Anyway, hit the “send” button and throw all of these models into the computer, and compare to what (we think) happened in the Eemian. It’s there for all to see in the paper’s Figure 3a (our Figure 2): The concatenated models’ gargantuan increases in sea level take place about 1,000 years before they were actually observed.

So there it is. As University of Colorado’s Roger Pielke, Sr., tweeted in response to the paper:

Maybe this is what happens when hypersensitive models are fed unrealistic data.

References:

DeConto, R.M., and D. Pollard. 2016. Contribution of Antarctica to past and future sea-level rise. Nature, 531, 591-597, doi:10.1038/nature17145. http://www.nature.com/nature/journal/v531/n7596/full/nature17145.html

Monaghan, A. J., D. H. Bromwich, and David P. Schneider, 2008. Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models. Geophysical Research Letters, 35, L07502, doi:10.1029/2007GL032630.

O’Donnell, R., N. Lewis, S. McIntyre, and J. Condon, 2011. Improved Methods for PCA-Based Reconstructions: Case Study Using the Steig et al. (2009) Antarctic Temperature Reconstruction. Journal of Climate, 24, 2099-2115.