The Current Wisdom only comments on science appearing in the refereed, peer-reviewed literature, or that has been peer-screened prior to presentation at a scientific congress.
Previous editions of Wisdom, which began in 2010, are available at our blog Cato@Liberty (www.cato-at-liberty.org/).
A major pillar supporting the catastrophic vision of climate change is a large and rapid rise in the level of the global oceans. There’s an awful lot of infrastructure and property by the shore – and people who live there. Total insured property values along the Atlantic coast of the U.S. (which includes the Gulf of Mexico) are roughly equal to the nation’s annual GDP.
So should you sell your beach house because of the impending doom? I say yes. You need to beat the rush, put it on the market at a bargain-basement price, and sell it to me. And then I will keep it until the cows come home.
In its Fourth Assessment Report (AR4) published in 2007, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) projected that sea levels would rise somewhere between 7 and 23 inches with a central value of about 15 inches by century’s end. Alarmists were quick to argue that these numbers were far too low because the IPCC did not include dynamic changes that may occur to the vast ice sheets located in Greenland and Antarctica. Since the publication of the AR4, a host of papers (e.g., Vermeer and Rahmstorf, 2009; Grinsted et al., 2009) have been published that suggest that a sea level rise of 3 to 6 feet by the year 2100 is a much more likely expectation than is 15 inches.
But, as we have noted previously in this Wisdom, many of the proposed mechanisms for such a rapid rise — which is caused by a sudden and massive loss of ice from atop Greenland and/or Antarctica — don’t seem to operate in such a way as to produce a rapid and sustained ice release.
But the rapid sea level rise beat goes on. In global warming science, we note, the number of scientific papers with the conclusion “it’s worse than we thought” vastly outnumbers those saying “new research indicates things aren’t so dire as previous projections.” In a world of unbiased models and data, they should roughly be in balance.
This just in: it’s worse than we thought! In research published last month, Eric Rignot and colleagues have combined observations and models to derive a history of the surface mass balance (SMB) of ice (gains from snowfall minus losses from surface melting and glacial discharge) over Greenland and Antarctica. What they find is that over the past two decades, the SMB of ice in both locations has gone from positive (i.e., net gains) to negative (i.e., net loss). In other words, the amount of ice was increasing annually on both landmasses back in the early 1990s, but now ice is currently being lost. And if that were not bad enough, the negative trend in SMB means that the rate of ice loss is increasing (i.e., ice loss is accelerating). The acceleration is about 50% greater in Greenland than it is in Antarctica.
Extrapolating the acceleration forward, Rignot et al. find that the combined ice loss from Greenland and Antarctica becomes the largest contributor to sea level rise by the mid-to-late 21st century, exceeding that from thermal expansion and ice loss from mountain glaciers in other parts of the world. This is a significant finding because in the AR4 the IPCC actually projects that, in combination, Greenland and Antarctica gain ice over the 21st century and thus act to retard the rise in sea level from other contributors. The implication from Rignot et al. is that the IPCC AR4 sea level rise projections for the end of the century (which average about 15 inches) are too low — by about 2 feet. Thus, Rignot et al. lends support for the recent projection of sea level rise over the 21st century of 3 feet or more (e.g., Vermeer and Rahmstorf, 2009; Grinsted et al., 2009).
So please stop here. Read no more, and, in a panic, sell me the house.
The SMB history for Antarctica and Greenland history is very noisy. The magnitude of recent trends (which are derived from less than 20 years worth of data) may not be terribly representative of the value of the long-term trend. Nor is the glacial behavior in Greenland and Antarctica well-understood; recent papers have suggested that a larger speed-up in the rates of glacial flow is likely not sustainable (see previous Current Wisdom articles for more details).
Now there is more.
We (my research team) just published a paper in the Journal of Geophysical Research in which we estimate the history of the extent of surface ice melt (a major component of SMB) in Greenland for the last two and a quarter centuries. Our goal was to provide some longer context it which to place the relatively short period of direct ice melt observations (such as those included in Rignot’s analysis). What we found is that, while the current rate of surface ice melt is high (and increasing), there have been times in the past (primarily from the late 1920s through the early 1960s) during which the ice melt across Greenland was just as high (Figure 1). And, this is important, the period of the lowest ice melt extent across Greenland for more than a century occurred from the early 1970s through the late 1980s – or very near the beginning the time period analyzed by Rignot et al.1
Figure 1. Reconstructed history of the total ice melt extent index over Greenland, 1784�2009. Observed values of the ice melt index (blue solid circles), reconstructed values of the ice melt index (gray open circles), the 10 year trailing moving average through the reconstructed and fitted values (thick red line), and the 95% upper and lower confidence bounds (thin gray lines) (from Frauenfeld et al., 2011).
We describe this in our paper:
