November 1, 2010 11:47PM

The Current Wisdom

The Current Wisdom  is 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.

 More Good News About Sea Level Rise

In the last (and first) installment of The Current Wisdom, I looked at how projections of catastrophic sea level rise—some as high as 20 feet this century—are falling by the wayside as more real-world data comes in. In the last month, there’s been even more hot-off-the-press studies that a) continue to beat down the notion of disastrous inundations, and b) received no media attention whatsoever.

Last month, I featured a new analysis which showed that the calibration scheme for satellite gravity measurements was out of whack, leading to an overestimation loss of glacial ice from Greenland and Antarctica by about 50%.   

This time around, there are two brand-new studies which further dampen the fears of rapid sea level rise spawned by a warming climate.  The one estimates that about 25% of the current sea level rise has nothing whatsoever to do with “global warming” from any cause, but instead is contributed by our increasing removal of fossil groundwater to suit our growing water demands. And the second estimates that the total sea level rise contribution of one of Antarctica’s biggest outlet glaciers—one which has been called “the weak underbelly” of the massive West Antarctic Ice Sheet—is most likely only going to be about 1/2 inch by the year 2100. Neither met the press, which is why you are reading about them here.

Last month we concluded that “things had better get cooking in a hurry if the real world is going to approach these popular estimates [3 to 20 feet of sea level rise by 2100]. And there are no signs that such a move is underway.” Now, there are even more signs that the massive sea level rise candle is flaming out as rapidly as cap-and-trade in an election year.

A team of scientists from the Netherlands, headed by the appropriately surnamed Yoshihide Wada, have been investigating the magnitude and trends of groundwater usage around the world. For millennia, humans  “mined” water under the surface, but the volumes were globally inconsequential.

Wada et al. found many regions, including the Midwestern and Southwestern U.S., in which groundwater extraction exceeds groundwater replenishment. Around the world, Wada et al. found that the total excess was about 30 cubic miles per year in 1960, which rose to about 68 by the year 2000.

What on earth does this have to do with sea-level rise?

Remember that, outside of nuclear reactions, matter is never destroyed.  Water taken out of the ground either runs off to a creek and makes it back to the ocean, or it evaporates.  Because the total water vapor concentration in the atmosphere is constant (depending upon the average temperature of the water/atmosphere interface), the additional evaporation is available for precipitation, adding to that which runs off.   

68 cubic miles of added water to the ocean each year amounts to about three-hundredths of an inch of sea level. Granted, this is a small amount, but (despite the scare headlines emanating from our greener friends), the annual rate of global sea level rise during the past 20 years has only been about 0.12 inches per year.  So groundwater extraction accounts for about a quarter (.03/.12) of the current rate of sea level rise.

This is a rather large bite out of the apple of sea level rise, and it means that estimates of just how much sea level rise is being caused by ongoing global warming have to be slashed.

In a much-hyped paper appearing in Science magazine back in early 2007, Stefan Rahmstorf and colleagues (including NASA’s infamous Cassandra James Hansen, the Nouriel Roubini of climatology), proclaimed that sea level rise is occurring at a rate which was at the very high end of the projections from the United Nations’ Intergovernmental Panel on Climate Change (IPCC)—fuelling claims that the IPCC sea level rise projections from climate change were too conservative.

(Hansen is also the lonely champion of the notion that sea level will rise 20 feet in the next 89 years.  Twenty years ago, he predicted that New York’s Westside Highway would be inundated by now.)[1]

If the Rahmstorf et al. analysis were updated through 2010 and the impact from groundwater depletion figured in, it would turn out that the observed rate of sea level rise from global warming would fall at or below the IPCC’s mid-range projection which ultimately results in about 15 inches of sea level rise by 2100. Such a finding of course would ignite very  little hype—which is why you are reading it here.

Ah, but you say, don’t the global warming doomsayers tell us that  the rate of sea level rise will accelerate rapidly as the climate warms and glaciers atop Greenland and Antarctica slip off into the seas, and so the total rise by the end of the century will be much above a value based on an extrapolation of the present?

The idea—graphically portrayed in Al Gore’s science fiction film—is that summer meltwater will flow down the, say, 10,000 feet required to get to the bottom of Greenland’s ice, and “lubricate” the flowing glaciers.  (Of course, the reason glaciers flow to begin with is because the pressure is so great that the bottom water is liquid, but never mind that fact).

Last time, I noted a recent paper by Faezeh Nick and colleagues that basically pooh-poohed the idea that surface meltwater does this. 

Offing the PIG

Another oft-repeated threat is that there are a plethora of glaciers in Antarctica that are grounded in the oceans, and that higher water temperatures will lead to melting from below that will ultimately “unground” them, floating them and causing rapid retreat.  

Alarmist fingers are most often pointed at Antarctica’s Pine Island Glacier (PIG), the leading candidate to unground and raise sea levels by up to 4.5 feet a relatively short amount of time.  It was Terence Hughes (from University of Maine’s Climate Change Institute, which—surprise—thrives on climate change) in the early 1980s that labeled the PIG as the “weak underbelly” of the West Antarctic Ice Sheet for, in his view, having the biggest potential to contribute a lot of sea level rise in a short amount of time.  Hughes’s belief has become popular of late as the rate of retreat of the PIG increased in the early 1990s.

In 2008,  University of Colorado’s Tad Pfeffer and colleagues projected that the PIG (and the nearby Thwaites glacier) would add between 4.3 and 15.4 inches of sea level rise by 2100.  In early 2010, the reliably alarmist New Scientist headlined “Major Antarctic Glacier ‘Past its Tipping Point’”, inaccurately quoting Oxford’s Richard Katz who actually said “the take-home message is that we should be concerned about tipping points in West Antarctica and we should do a lot more work to investigate” (translation: can I scare you into sending me more money?).

But throwing cold water in the PIG pen are the prolific polar researcher Ian Joughin and his colleagues.  In a new paper published in Geophysical Research Letters, Joughin et al. reported their efforts to simulate the future behavior of PIG using a “basinscale glaciological model” that they verified against a large amount of satellite observations documenting the flow rate and thinning rate of the PIG. Once they were happy that their model depicted the observations correctly, they turned to look at what the future may hold in store.

What they found came as a bit of a surprise. 

Instead of an accelerating retreat, it seems that the PIG’s still-tiny decline may remain constant. Joughin et al., write:

PIG’s dramatic retreat and speedup may not indicate a trend of continued acceleration, and speeds may stabilize at their current elevated levels as thinning continues.

This result ties into another investigation of  recent PIG behavior that was published this summer.  In that one, Jenkins et al. concluded that the geometry of the sea floor upon which the PIG rested is what allowed for a rapid retreat when warming first commenced. In other words, the PIG was predisposed to a rapid response—initially.

When Joughin et al. plug potential future climate change into their glaciological model of PIG, they found that the initial acceleration is not maintained for very long, and instead soon stabilizes. This has large implications. Instead of PIG contributing many inches of sea level this century, they found about a single inch—and that was the worst case.  Joughin and colleagues best estimate is something closer to ½ inch.

Joughin et al. conclude:

While we have not modeled the other [nearby Antarctic] glaciers, PIG is the most rapidly changing and largest contributor to the current imbalance, indicating future model-derived upper bounds on 21st century sea level for the entire region are likely to fall well below the heuristically derived 11-to-39 cm upper bound [Pfeffer et al., 2008].

Hardly catastrophic.

Sooner or later, these facts may penetrate into public consciousness... but until then I hope you’ll continue to consult The Current Wisdom.


Hughes, T. J., 1981, The Weak Underbelly of the West Antarctic Ice-Sheet. Journal of Glaciology, 27, 518–525.

Jenkins, A., et al., 2010. Observations Beneath Pine Island Glacier in West Antarctica and Implications for its Retreat. Nature Geoscience, 3(7), 468–472, doi:10.1038/ngeo890.

Katz, R. F., and  M. G. Worster, 2010. Stability of Ice-sheet Grounding Lines. Proceedings of the Royal Society A, 466, 1597-1620.

Nick, F. M., et al., 2009. Large-scale Changes in Greenland Outlet Glacier DynamicsTtriggered at the Terminus. Nature Geoscience, DOI:10.1038, published on-line January 11, 2009.

Pfeffer, W. T., Harper, J. T., and S. O’Neel, 2008. Kinematic Constraints on Glacier Contributions to 21st-century Sea-level Rise. Science, 321, 1340-1343.

Rahmstorf, S., et al., 2007. Recent Climate Observations Compared to Projections. Science, 316, 709.

Joughin, I., Smith, B. E., and D. M. Holland, 2010. Sensitivity of 21st Century Sea Level to Ocean-induced Thinning of Pine Island Glacier, Antarctica. Geophysical Research Letters, 37, L20502, doi:10.1029/2010GL044819.

Wada, Y., et al. 2010. Global Depletion of Groundwater Resources. Geophysical Research Letters, 37, L20402, doi:10.1029/2010GL044571.


[1] In 1988, author Robert Reiss asked Hansen, whose office is on Broadway, what greenhouse-effect changes would occur in the next twenty years.  He said, among other things, “The West Side Highway [which runs along the Hudson River] will be under water. And there will be tape across the windows across the street because of high winds. And the same birds won’t be there. The trees in the median strip will change.” Then he said, “There will be more police cars.” Why? “Well, you know what happens to crime when the heat goes up.”