Listeners to Radio 4’s Today programme – and this includes much of the political elite – will have been alarmed to be told that “the Arctic could be ice-free on a summer’s day by the end of the decade”.
Yet the evidence for this “trend” turns out to be drawn from less than two years worth of data.
Dr Seymour Laxon of University College London raised the alarm using radar altimeter observations made by the European-funded Cryosat-2 satellite, a project he helped devise. This allows scientists to gain more accurate mapping of the sea floor and also sea ice extent and thickness.
Cryosat-2 began observing the Arctic ice cap in October 2010, and has been acquiring data since. So scientists have two winter seasons and one summer season on which to base any claims.
Is this a problem? Actually, according to the European Space Agency, it is. “Three to four years of data from Cryosat-2 can be averaged to reduce the ‘noise’ due to currents and tides and better chart the permanent topography related to marine gravity,” it stated.
Using less than three or four years of data is frowned upon – and that’s official.
In addition, Dr Laxon himself recommends using much longer timescales. As he wrote in a 2003 paper (High interannual variability of sea ice thickness in the Arctic region Laxon, Peacock and Smith, Nature), “the sea ice mass can change by up to 16 per cent within one year” and “this variability must be taken into account when determining the significance of trends”.
So how can Dr Laxon now justify using an inadequate data set to make a long-term claim? Alas, we don’t know. The tenacious questioning that Today typically gives to guests was suspended for this segment, and Laxon was received with the deference a Pope receives when lecturing his cardinals. The claim went unchallenged.
Arctic ice is cited by catastrophists as a potential “tipping factor” (or “hysteretic threshold behavior”) for two reasons. Cooler water may affect oceanic circulation, with consequences for countries south of the ice cap. And less ice may decrease the albedo.
Yet the true picture is complicated. Ice extent has varied much more dramatically in the past, long before global-warming skeptical Top Gear was conceived or broadcast. Research published in the peer-reviewed Canadian Journal of Earth Sciences [PDF, 1.1MB] in 2008 looked at the Western Arctic, and noted that “the amplitude of these millennial-scale changes in sea-surface conditions far exceed those observed at the end of the 20th century”.
Without causing a tipping.
Climate policy blogger Ben Pile has put together a roundup of “ice free” Arctic claims. “The alarmist story is allowed to proceed in spite of facts, and without scrutiny or criticism,” he observed.
Scientists despair of the public’s waning interest in climate change, and like to blame disinformation. They only have themselves to blame.