Policy Peril Segment 4 – Sea Level Rise

In An Inconvenient Truth, Al Gore warns that global warming could raise sea levels by 20 feet, and he implies that this could happen quite suddenly–in our lifetimes or those of our children.

Specifically, on pp. 204-206 of the book version of AIT, Gore warns that if half the Greenland Ice Sheet and half the West Antarctic Ice Sheet melted or broke up and slipped into the sea, some 100 million people living in Beijing, Shanghai, Calcutta, and Bangladesh would  “be displaced,” “forced to move,” or “have to be evacuated.”  Is there any truth to it?

Today’s clip from CEI’s film Policy Peril: Why Global Warming Policies Are More Dangerous Than Global Warming Itself, again features Dr. Patrick Michaels of the Cato Institute, former Virginia State Climatologist, author of several superb books (most recently, Climate of Extremes: The Global Warming Science They Don’t Want You to Know), and prolific blogger on World Climate Report.

Here are my previous posts in this series:

To watch today’s video clip, click here. To watch Policy Peril from start to finish, click here.

The text of today’s excerpt immediately follows. It includes some graphics from the film and footnotes to the pertinent scientific literature.

Dr. Patrick Michaels: This even as there is a purported large melt of ice from Greenland. It turned around — the thermohaline circulation became stronger. [1] 

Narrator: Hmm. These facts are inconvenient only for the makers of An Inconvenient Truth. But who can forget the scenes where a 20-foot wall of water rolls across the world’s coastal communities. In the book version [of AIT], Gore says, “If Greenland melted or broke up and slipped into the sea–or if half of Greenland and half of Antarctica melted or broke up and slipped into the sea–sea levels worldwide would increase by 18 to 20 feet.” Reality check! How much ice is Greenland shedding?

Dr. Michaels: The actual loss of ice from Greenland is about 25 cubic miles per year. [2] Now, if that seems like a lot, there are about 700,000 cubic miles of ice on Greenland. The loss rate is four-tenths of one percent of its ice mass, per century. I didn’t say per year. I didn’t say per decade. I said four-tenths of one percent per century[3]

Narrator: That translates into how much sea-level rise?

Dr. Michaels: If you take a look at the IPCC’s latest volume, by the year 2100, they have two inches of sea-level rise resulting from the loss of Greenland ice. Not two feet. Not 20 feet. Two inches! [4] That’s the “consensus of scientists,” okay. Whether or not we believe in consensus science, that’s what they say.

Narrator:  Gore says global warming could melt half of Greenland. Is that plausible?

Dr. Michaels: The United Nations [IPCC] projects that if we raise carbon dioxide to four times the background level–that would be about 1,100 parts per million, right now we’re at about 385 parts per million–and maintain that for 1,000 years, that Greenland would lose about half its ice in a millennium. [5] Now, we don’t have enough fossil fuel to maintain that concentration for 1,000 years.

Narrator: Gore also says half the ice sheet could break off because of “moulins.” For me, this was the scariest part of  An Inconvenient Truth. Moulins are cracks that channel meltwater from the surface of the ice sheet to the bedrock below. By lubricating the bedrock, moulins could destabilize the ice sheet, Gore says. [6]


Well, a recent study in Science magazine lays that fear to rest. A small meltwater lake poured down a moulin at a flow rate exceeding that of Niagara Falls. [7] Yet, Science magazine reports, “For all the lake’s water dumped under the ice that day, and all the water drained into new moulins in the following weeks, the ice sheet moved only an extra half meter near the drained lake.” [8] An extra half meter. [9]


[1] The thermohaline circulation “became stronger.” Dr. Michaels (Pat to his friends] just finished debunking Gore’s claim that ice melt from Greenland will inject enough fresh water into the North Atlantic to disrupt the thermohaline circulation (THC, a.k.a. oceanic “conveyor belt”), which most scientists–though not Richard Seager of Columbia University’s Lamont-Doherty Earth Observatory–believe is responsible for Europe’s mild winters. There was a brief scare about THC shutdown a few years ago when Bryden et al. (2005) reported that the Atlantic branch of the conveyor belt slowed by 30% between 1957 and 2004. But one year later, Richard Kerr of Science magazine reported on new data showing that the Bryden study was a “false alarm.” In fact, Dr. Michaels says, alluding to Boyer et al. (2006) and Latif et al. (2006), the THC became stronger. The Center for the Study of Carbon Dioxide and Global Change reviews Latif et al. (2006) here, and reviews many other THC studies. I discuss Gore’s warming-causes-cooling fantasy on pp. 11-12 of my April 2007 testimony before the Colorado Republican Study Committee.

[2] The estimate of 25 cubic miles of Greenland ice loss per year comes from Luthcke et al. (2006), a study summarized here on NASA’s Web page.

[3] Greenland has approximately 3 million cubic kilometers of ice. To convert cubic kilometers into cubic miles, you multiply the number of cubic kilometers by 0.2399. Hence, Greenland has about 719,000 cubic miles of ice. It is losing about 25 cubic miles of ice per year, which translates into a rate of 2,500 cubic miles per century. 2,500 is 4/10ths of 1% of 719,000.

[4] In the IPCC’s mid-range emissions scenario (A1B), Greenland ice loss contributes between 1 centimeter (cm) and 8 cm of sea-level rise in the 21st Century; in the IPCC’s high-end emissions scenario (A1FI), Greenland ice loss contributes between 2 cm and 12 cm per year (IPCC AR4 WGI, Chapter 10: Climate Change Protections, Table 10.7, p. 820). Translating into inches, Greenland ice loss contributes between 0.4 and 3.1 inches in mid-range A1B emissions scenario and between 0.7 and 4.7 inches in A1FI high-end emissions scenario.

[5] Pat here refers to Ridley et al. (2005), as reviewed in Chapter 10 of IPCC AR4 WGI, on p. 830. The figure below shows what the researchers project would happen to Greenland’s ice if carbon dioxide concentrations increase to four times pre-industrial levels and stay there for 3,000 years.


[6] Gore’s photograph and diagram of moulins come from Zwally et al. (2002), published in Science magazine.


In AIT, Gore animates the diagram so that the ice sheet begins to break apart at the E.Q. (equilibrium) line. This is thoroughly misleading. The E.Q. line of an ice sheet is the elevation at which glacier melting and snow accumulation are equal. Above the E.Q. line, snow accumulation exceeds ice melt; below it, ice melt exceeds snow accumulation. The E.Q. line is not a fault line or fissure in the ice.

More importantly, Zwally et al. (2002) is not evidence of an impending ice sheet crackup. The researchers found that moulins associated with summer ice melt accelerate glacial flow, but only by a few percent. For example, the flow rate of one outlet glacier increased from 31.3 cm/day in winter to 40.1 cm in July, falling back to 29.8 cm in August, increasing annual movement by about 5 meters. Apocalypse not!

[7] In a study updating the Zwally team’s research, Joughin et al. (2008) found somewhat more glacier acceleration associated summer ice melt and moulins. However, the study’s bottom-line conclusion is pointedly non-apocalyptic:

Surface-enhanced basal lubrication has been invoked previously as a feedback that would hasten the ice sheet’s demise in a warming climate. Our results show that several fast-flowing outlet glaciers, including Jakobshavn Isbrae, are relatively insensitive to this process . . . Our results thus far suggest that surface-melt enhanced lubrication will have a substantive but not catastrophic effect on the Greenland Ice Sheet’s future evolution.

[8] In a companion article (cited in this Policy Peril excerpt), Science magazine reporter Richard Kerr quotes Pennsylvania State University glaciologist Richard Alley on moulin-induced ice sheet lubrication:

“Is it run for the hills, the ice is falling into the ocean?” asks Alley. “No, it matters but it’s not huge.”

 Kerr goes on to observe, as noted above, that an entire 4 km-long, 8 m-deep melt-water lake disappeared down a moulin in about 1.4 hours–at an average rate of 8,700 cubic meters per second, “exceeding the average flow rate of Niagara Falls.” Yet, despite all the water dumped under the ice that day and all the water drained into new moulins in the following weeks, the ice sheet moved only “an extra half meter near the drained lake.” 

[9] To put the extra half meter of glacial movement in perspective, consider that the Greenland Ice Sheet extends 2,530 kilometers (1,570 miles) North-South and has a maximum width of 1094 kilometers (680 miles) near its northern margin.

In a segment of Policy Peril immediately following today’s film excerpt, Pat also discusses studies in Science magazine indicating that the West Antactic Ice Sheet (WAIS) is more stable than scientists previously believed. The researchers found that outlet glaciers drag debris under the ice that piles up into “wedges.” These hidden land forms then prop up and stabilize the ice shelf.


The significance? Scientists once worried that sea-level rise of just a few feet could lift the WAIS off its island moorings, hastening its break up and demise. However, as Anderson (2007)  reports in Science magazine, in a review of Anandakrishnan et al. (2007) and Alley et al. (2007) and their discovery of  stabilizing land forms under the WAIS, “At the current rate of sea level rise, it would take several thousand years to float the ice sheet off its bed.”

A more recent study by Pollard and DeConto (2009), reviewed by the Center for the Study of Carbon Dioxide and Global Change, concludes that “the WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5ºC.” How long would that take? 

In a companion article, Huybrechts (2009) estimates that, “The required ocean warmings, on the order of 5ºC, may well take several centuries to develop.” He asserts that “such an outcome could result from the accumulation of greenhouse-gas emissions projected for the twenty-first Century, if emissions are not greatly reduced.” His source here, however, is simply the IPCC report with its questionable assumptions about climate feedbacks and sensitivity. Huybrechts continues:

The implied transition time for a total collapse of the West Antarctic ice sheet of one thousand to three thousand years [in Pollard and DeConto (2009)] seems rapid by Antarctic standards. But it is nowhere near the century timescales of West Antarctic ice sheet decay based on simple marine ice-sheet models. 

And one to three thousand years is certainly nowhere near the years-to-decades innundation of the world’s coastal communities that Al Gore conjures up in An Inconvenient Truth.