Karl Popper and Antarctic Ice
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OVER THE PAST THIRTY OR MORE YEARS, the scientific community has become increasingly certain that the introduction of huge amounts of greenhouse gases into the atmosphere is causing average global temperatures to rise, and that this rise will likely lead to a number of undesirable results [IPCC 2007]. However, this claim has caused a great deal of controversy, and has become a key political issue in contemporary American politics. The general public has taken sides, with only 11% of voters being undecided on the question of whether humans are responsible for global warming according to a Rasmussen poll taken last month [Rasmussen 2010]. Unfortunately, the scientific quality of the debate leaves something to be desired. Analyzing the talking points on both sides with any attempt at being comprehensive would require a very long book, so I have chosen to focus on one particular example that illustrates many of the problems involved.
Though slightly less common at the current moment, a popular argument against global warming a few years ago was the apparent growth of the Antarctic ice cap. If global warming were true, the argument ran, then ice in Antarctica ought to be melting instead of accumulating! Senator James Inhofe's official blog on the Senate website ran a typical headline in March, 2008: “Media Hype on ‘Melting’ Antarctic Ignores Record Ice Growth” [Morano 2008]. The post goes on to criticize the hype over the “allegedly dire consequence of man-made global warming,” and to claim that 2007 and 2008 were the “tipping point” where “climate alarmism” was finally starting to be disproven.
If we reconstruct the argument, it goes something like this: global warming predicts an increase in global temperatures. If there is an increase in global temperatures, then ice should melt more easily and there should be less ice on the poles. However, the amount of ice in the Antarctic is increasing. This increase is proof that temperatures are not rising, and therefore that global warming is wrong. To go back to our initial discussion, this is very good Popperian science. You look at the predictions and the actual facts, and if they don't line up, then you throw the theory out. Unfortunately, the reality is much more complicated than that. Every step of that argument is subject to a great deal of legitimate scientific disagreement, and Antarctic ice is not, in fact, a nail in the coffin for the theory of global warming.
The first question is to determine whether the amount of ice in the Antarctic ice sheet is increasing or decreasing. This is, perhaps surprisingly, far from straightforward. A number of different measurement techniques have been used to study the question, and the results have disagreed. In 1992, a review of all of the attempts to measure Antarctic ice determined that no conclusion could be reached at that time, and that the data was consistent with anything from a yearly increase of 600 gigatons to a yearly decrease of 500 gigatons of ice [Jacobs 1992].
Of course, more studies have been done since then. The case for increasing Antarctic ice was bolstered in 2005 when a team led by Curt Davis found that the East Antarctic Ice Sheet “increased in mass by 45 ± 7 billion metric tons per year from 1992 to 2003,” while the West Antarctic Ice Sheet didn't change much [Davis 2005]. They used satellites as well, in their case to measure the altitude of 8.5 million square kilometers of this ice sheet. They found that it was thickening at a rate of about 1.8 centimeters per year.
The results obtained from this study and others like it were good evidence that Antarctica was gaining ice. However, these studies were far from perfect, and there was one big question in particular: What was happening to the ice on the coasts? Coastal ice dynamics are difficult to model, and can have a potentially huge impact if a lot of ice is flowing out to the sea. The Davis study warned at the end that “these results have only sparse coverage of the coastal areas where recent dynamic changes may be occurring. Thus, the overall contribution of the Antarctic ice sheet to global sea-level change will depend on the balance between mass changes on the interior and those in coastal areas.” They cited a 2004 study which used measurement techniques similar to their own on the Western Antarctic coast, and got results that suggested that this discharge of ice was happening at a pretty fast rate [Thomas 2004]. The question boiled down to: Is mainland ice increasing fast enough to outweigh the loss of ice on the coasts? The good money was still on an Antarctic ice increase, but the issue was far from settled.
