Joanne Nova posts about a new paper (Frezzotti et al 2013)on Antarctica; her headline … Antarctica gaining Ice Mass – and is not extraordinary compared to 800 years of data. If all you did was read her headline, you might be tricked into thinking that global warming was not happening, a conclusion that is not shared by the paper’s authors.
The paper “A synthesis of the Antarctic surface mass balance during the last 800 yr” is reporting on Surface Mass Balance (SMB) in Antarctica. Nova confuses this with the Total Mass Balance of Antarctica, an entirely different property. In typical fashion Nova draws her own conclusion … “As far as we can tell, the Antarctic Ice Sheet (AIS) is growing”, – something the research paper does not say or support.
Surface Mass Balance = New Snow
Total Mass Balance = New Snow – Ice Melt
SMB is a measurement of how much new snow accumulates on the existing ice sheets each year, whilst Total Mass Balance is calculated from the New Snow minus Ice Melt. Frezzotti 2013 suggests SMB is around 2,100 Gigatons per year, but the paper does not attempt to calculate the amount of melted ice; this was not the purpose of this paper. It only sought to examine the SMB.
Nova mistakenly (stupidly?) thinks that the SMB (Deposits) represents the Total Change in Mass (Deposits – Withdrawals) and makes a comparison between the 2,100 Gigatons amount (Deposits) against that of a previous presentation for Total Mass Balance (Deposits – Withdrawals) …
The Surface Mass Balance appears to be growing at 2100Gt/year (though this is much higher than the ICESAT satellite estimates of Zwally which estimate a net gain of 49Gt/year.)
Climate model projections based on increasing greenhouse gas concentrations predict a warmer atmosphere containing higher levels of water vapour, suggesting that the Antarctic snowfall is expected to increase. Thus, the SMB of the AIS will negatively contribute to sea level rise … Approximately 75% of the predicted precipitation increase will fall in peripheral areas with surface elevations below 2250m (Genthon et al., 2009). Recent satellite observations indicate an accelerating ice loss in these peripheral areas due to ongoing and past glacier acceleration, implying that the contribution of ice sheets to sea level rise increases over time …
Of course, if you’re stupid enough to look only at Deposits and ignore the melting ice, then yes, you’ll draw the conclusion (like Nova has) that the Antarctic is growing. But what does real science have to say?
Antarctic Ice is NOT Growing
Nova references a presentation report (by Zwally – not a published journal paper, but something that was put together as serious effort to understand what is happening in Antarctica). This presentation estimated an net gain of 49Gt per year, and because that suggested Antarctica was growing, this presentations was an immediate hit around denialist websites. But what happened next?
The data in the presentation didn’t agree with other research, the experts, including Zwally, re-examined al of the data and produced this report … A Reconciled Estimate of Ice-Sheet Mass Balance .. which says …
We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.
The Antarctic is melting. The accumulating snow is not compensating for the loss of melting ice.
A good scientific view is obtained by not just cherry picking one piece of data or one report (like Nova does), but by considering all lines of evidence.
In the last few decades, glaciers at the edge of the icy continent of Antarctica have been thinning, and research has shown the rate of thinning has accelerated and contributed significantly to sea level rise.
New ice core research suggests that, while the changes are dramatic, they cannot be attributed with confidence to human-caused global warming, said Eric Steig, a University of Washington professor of Earth and space sciences.
… The same is not true for the Antarctic Peninsula, the part of the continent closer to South America, where rapid ice loss has been even more dramatic and where the changes are almost certainly a result of human-caused warming, Steig said.
New research from the Antarctic Peninsula shows that the summer melt season has been getting longer over the last 60 years. Increased summer melting has been linked to the rapid break-up of ice shelves in the area and rising sea level.
A new 1000-year Antarctic Peninsula climate reconstruction shows that summer ice melting has intensified almost ten-fold, and mostly since the mid 20th Century. Summer ice melt affects the stability of Antarctic ice shelves and glaciers.
A new study funded by the National Science Foundation (NSF) finds that the western part of the massive West Antarctic Ice Sheet (WAIS) is experiencing nearly twice as much warming as previously thought.
None of these articles were presented by Nova, instead she chose one because she mistakenly believed it showed Antarctica had been increasing in mass. Instead she just demonstrated her lack of basic knowledge. A great example of why you should defer to the experts rather than bloggers – yes that includes myself. I’ll be delighted if people read the science directly from the source rather than interpreted by bloggers biased by a political agenda.