The Current Wisdom
NOTE: This is the first in a series of monthly posts in which Senior Fellow Patrick J. Michaels reviews interesting items on global warming in the scientific literature that may not have received the media attention that they deserved, or have been misinterpreted in the popular press.
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.
The Iceman Goeth: Good News from Greenland and Antarctica
How many of us have heard that global sea level will be about a meter—more than three feet—higher in 2100 than it was in the year 2000? There are even scarier stories, circulated by NASA’s James E. Hansen, that the rise may approach 6 meters, altering shorelines and inundating major cities and millions of coastal inhabitants worldwide.
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Figure 1. Model from a travelling climate change exhibit (currently installed at the Field Museum of natural history in Chicago) of Lower Manhattan showing what 5 meters (16 feet) of sea level rise will look like.[/caption]In fact, a major exhibition now at the prestigious Chicago Field Museum includes a 3-D model of Lower Manhattan under 16 feet of water—this despite the general warning from the James Titus, who has been EPA’s sea-level authority for decades:
Researchers and the media need to stop suggesting that Manhattan or even Miami will be lost to a rising sea. That’s not realistic; it promotes denial and panic, not a reasoned consideration of the future.
Titus was commenting upon his 2009 publication on sea-level rise in the journal Environmental Research Letters.
The number one rule of grabbing attention for global warming is to never let the facts stand in the way of a good horror story, so advice like Titus’s is usually ignored.
The catastrophic sea level rise proposition is built upon the idea that large parts of the ice fields that lay atop Greenland and Antarctica will rapidly melt and slip into the sea as temperatures there rise. Proponents of this idea claim that the United Nations’ Intergovernmental Panel on Climate Change (IPCC), in its most recent (2007) Assessment Report, was far too conservative in its projections of future sea level rise—the mean value of which is a rise by the year 2100 of about 15 inches.
In fact, contrary to virtually all news coverage, the IPCC actually anticipates that Antarctica will gain ice mass (and lower sea level) as the climate warms, since the temperature there is too low to produce much melting even if it warms up several degrees, while the warmer air holds more moisture and therefore precipitates more snow. The IPCC projects Greenland to contribute a couple of inches of sea level rise as ice melts around its periphery.
Alarmist critics claim that the IPCC’s projections are based only on direct melt estimates rather than “dynamic” responses of the glaciers and ice fields to rising temperatures.
These include Al Gore’s favorite explanation—that melt water from the surface percolates down to the bottom of the glacier and lubricates its base, increasing flow and ultimately ice discharge. Alarmists like Gore and Hansen claim that Greenland and Antarctica’s glaciers will then “surge” into the sea, dumping an ever-increasing volume of ice and raising water levels worldwide.
The IPCC did not include this mechanism because it is very hypothetical and not well understood. Rather, new science argues that the IPCC’s minuscule projections of sea level rise from these two great ice masses are being confirmed.
About a year ago, several different research teams reported that while glaciers may surge from time to time and increase ice discharge rates, these surges are not long-lived and that basal lubrication is not a major factor in these surges. One research group, led by Faezeh Nick and colleagues reported that “our modeling does not support enhanced basal lubrication as the governing process for the observed changes.” Nick and colleagues go on to find that short-term rapid increases in discharge rates are not stable and that “extreme mass loss cannot be dynamically maintained in the long term” and ultimately concluding that “[o]ur results imply that the recent rates of mass loss in Greenland’s outlet glaciers are transient and should not be extrapolated into the future.”
But this is actually old news. The new news is that the commonly-reported (and commonly hyped) satellite estimates of mass loss from both Greenland and Antarctica were a result of improper calibration, overestimating ice loss by some 50%.
As with any new technology, it takes a while to get all the kinks worked out. In the case of the Gravity Recovery and Climate Experiment (GRACE) satellite-borne instrumentation, one of the major problems is interpreting just what exactly the satellites are measuring. When trying to ascertain mass changes (for instance, from ice loss) from changes in the earth’s gravity field, you first have to know how the actual land under the ice is vertically moving (in many places it is still slowly adjusting from the removal of the glacial ice load from the last ice age).
The latest research by a team led by Xiaoping Wu from Caltech’s Jet Propulsion Laboratory concludes that the adjustment models that were being used by previous researchers working with the GRACE data didn’t do that great of a job. Wu and colleagues enhanced the existing models by incorporating land movements from a network of GPS sensors, and employing more sophisticated statistics. What they found has been turning heads.
Using the GRACE measurements and the improved model, the new estimates of the rates of ice loss from Greenland and Antarctica are only about half as much as the old ones.
Instead of Greenland losing ~230 gigatons of ice each year since 2002, the new estimate is 104 Gt/yr. And for Antarctica, the old estimate of ~150 Gt/yr has been modified to be about 87 Gt/yr.
How does this translate into sea level rise?
It takes about 37.4 gigatons of ice loss to raise the global sea level 0.1 millimeter—four hundredths of an inch. In other words, ice loss from Greenland is currently contributing just over one-fourth of a millimeter of sea level rise per year, or one one-hundreth of an inch. Antarctica’s contribution is just under one-fourth of a millimeter per year. So together, these two regions—which contain 99% of all the land ice on earth—are losing ice at a rate which leads to an annual sea level rise of one half of one millimeter per year. This is equivalent to a bit less than 2 hundredths of an inch per year. If this continues for the next 90 years, the total sea level rise contributed by Greenland and Antarctica by the year 2100 will amount to less than 2 inches.
Couple this with maybe 6-8 inches from the fact that the ocean rises with increasing temperature, temperatures and 2-3 inches from melting of other land-based ice, and you get a sum total of about one foot of additional rise by century’s end.
This is about 1/3rd of the 1 meter estimates and 1/20th of the 6 meter estimates.
Things had better get cooking in a hurry if the real world is going to approach these popular estimates. And there are no signs that such a move is underway.
So far, the 21st century has been pretty much of a downer for global warming alarmists. Not only has the earth been warming at a rate considerably less than the average rate projected by climate models, but now the sea level rise is suffering a similar fate.
Little wonder that political schemes purporting to save us from these projected (non)calamities are also similarly failing to take hold.
References:
Nick, F. M., et al., 2009. Large-scale changes in Greenland outlet glacier dynamics triggered at the terminus. Nature Geoscience, DOI:10.1038, published on-line January 11, 2009.
Titus, J.G., et al., 2009. State and Local Governments Plan for Development of Most Land Vulnerable to Rising Sea Level along the U.S. Atlantic Coast, Environmental Research Letters 4 044008. (doi: 10.1088/1748-9326/4/4/044008).
Wu, X., et al., 2010. Simultaneous estimation of global present-day water treansport and glacial isostatic adjustment. Nature Geoscience, published on-line August 15, 2010, doi: 10.1038/NGE0938.
