The Global Warming Policy Foundation doesn’t understand second derivatives!

I noticed the following tweet from the Global Warming Policy Foundation

Polar Ice Melt May Be Natural Event http://t.co/XrPKOjIY9c via @sharethis

— The GWPF (@TheGWPF) July 16, 2013

The link goes to a press release also stating that the Polar Ice Melt May be a Natural Event.

The press release itself seems to simply copy what was probably released by some university press office, but the title and tweet are clearly intended to imply that the melting observed in the polar regions is natural and not a consequence of anthropogenic global warming (AGW).

This press release appears to be referring to a recent Nature Geoscience paper called Limits in detecting acceleration of ice sheet mass loss due to climate variability. Below I include the abstract of the paper

The Greenland and Antarctic ice sheets have been reported to be losing mass at accelerating rates1, 2. If sustained, this accelerating mass loss will result in a global mean sea-level rise by the year 2100 that is approximately 43 cm greater than if a linear trend is assumed2. However, at present there is no scientific consensus on whether these reported accelerations result from variability inherent to the ice-sheet–climate system, or reflect long-term changes and thus permit extrapolation to the future3. Here we compare mass loss trends and accelerations in satellite data collected between January 2003 and September 2012 from the Gravity Recovery and Climate Experiment to long-term mass balance time series from a regional surface mass balance model forced by re-analysis data. We find that the record length of spaceborne gravity observations is too short at present to meaningfully separate long-term accelerations from short-term ice sheet variability. We also find that the detection threshold of mass loss acceleration depends on record length: to detect an acceleration at an accuracy within ±10 Gt yr−2, a period of 10 years or more of observations is required for Antarctica and about 20 years for Greenland. Therefore, climate variability adds uncertainty to extrapolations of future mass loss and sea-level rise, underscoring the need for continuous long-term satellite monitoring.

So, this is not about ice loss as such, it is about whether or not it is accelerating. The claim in the paper is that to determine if the acceleration is a long-term trend, 10 years or more is needed for Antarctica while 20 years or more is needed for Greenland. There’s no real disagreement about whether the ice mass loss in the polar regions is being driven by AGW (it is) there is simply some debate about whether or not the recent acceleration is a natural fluctuation or an indication of a human-induced acceleration. The basic point being that if we want to determine the long-term trends for Antarctic and Greenland ice-mass-loss we need to know if this acceleration is just a short-term variation or not. If not, the resulting sea-level rise by 2100 will be smaller than if it is a long-term acceleration of the ice-mass-loss.

Watts Up With That (WUWT) seems to be making a similar mistake by claiming Dueling press releases on ice melt – one says ‘uncertainty is large’ the other quantifies a number. This post compares two press releases about two different papers, one of which is the one I discuss above. This WUWT post certainly makes a big deal out of the suggestion in the above paper that the “uncertainty is large”. Sure, but there’s not much uncertainty about whether or not melting is taking place in Antarctica and Greenland. There’s just uncertainty about whether or not it is accelerating and hence there is uncertainty about the associated sea-level rise in 2100.

The other study quoted in the WUWT post seems to be a study that combines the Earth’s climate history with computer models to predict what sea-level rises we should expect for certain increases in surface temperature. The study I discuss above was, on the other hand, using satellite observations of the polar ice to determine the rate of change and possible acceleration. They’re essentially different types of studies. One was trying to establish if we could make a prediction about sea-level rises at a given point in time in the future (based on current loss rates and accelerations) the other was trying to determine the total sea-level rise after a given change in surface temperature using past climate history and computer models.

If Anthony had given this some thought he should have realised that these two studies are probably entirely consistent with each other. I will be generous and accept that the GWPF and WUWT may simply have misunderstood these studies rather than them intentionally mis-representing what these studies were suggesting. Others may, of course, disagree with this assessment.