Is the New UN Global Warming Report Too Conservative?

by Brett Clark and John Bellamy Foster

Not surprisingly, this new report, which was the product of hundreds of scientists (150 lead authors with 450 contributing authors) and had to be unanimously approved by 154 governments, including the United States and other major oil-producing countries, is shrouded in controversy. However, rather than arising from global warming naysayers, the principal challenge to the report this time comes from leading climatologists themselves, who view this new IPCC report as too conservative, underestimating the risks of global climate change.

Commenting on the IPCC's record with climate change projections, James Hansen, Director of the NASA Goddard Institute for Space Studies and widely considered to be the world's foremost climatologist, explained that the "IPCC has not overstated or overestimated those changes. The changes of carbon dioxide have been very accurate. Temperatures actually increased somewhat faster than projections. And sea level has increased notably faster than the prior estimates by IPCC" ("Gorilla of Sea Level Rise," Living on Earth, February 2, 2007). Yet, if the IPCC has in no way erred by overestimating the dangers, the same cannot be said with respect to underestimating them. Hansen and other leading climatologists insist that the new IPCC report fails to provide projections of sea level rise that are consistent with rising global temperature.

As the ocean warms due to increasing global temperature, it also expands, causing the sea level to rise. Melting glaciers and ice sheets are also increasing the volume of water. Destabilization of the ice sheets in Greenland and Antarctica would result in big increases -- to be measured in feet rather than inches -- in sea level. Nonetheless, the new IPCC report estimates an increase in sea level of only 18 to 59 centimeters (0.6-1.9 feet) this century -- an estimate even lower than in its 2001 report. Some experts have voiced strong dissent regarding these calculations (see "Experts Slam Upcoming Global Warming Report," CNN.com). Hansen points out that the IPCC center point of 3°C (5.4°F) increase in global average temperature is "inconsistent with the numbers that they gave for sea level," because they do not take into account the contribution of melting ice sheets ("Gorilla of Sea Level Rise").

In an article in Science (January 19, 2007), Stefan Rahmstorf "connects global sea-level rise to global mean surface temperature." In establishing this relationship, Rahmstorf projects a "sea-level rise in 2100 of 0.5 to 1.4 meters [1.6-4.6 feet] above the 1990 level." Hansen and his colleagues at the Goddard Institute observed in an article entitled "Global Temperature Change" published in the Proceedings of the National Academy of Sciences on September 26, 2006, that the temperature of the earth is now at the Holocene maximum and within approximately 1°C (1.8°F) of the maximum temperature of the last million years when the sea level was maybe as much as 5 meters (16 feet) higher than today. At a time when the earth's temperature was 2-3°C (3.6-5.4°F) warmer than today in the Middle Pliocene three million years ago, the sea level was 25-35 meters (80 feet or more) higher. As Hansen notes, based on this and other research:

We do have a lot of information available to us both from paleoclimate; the history of the earth and how ice sheets responded in the past and also the new data from satellites, and on surface measurements on the ice sheets which shows that there are processes beginning to happen there, exactly the processes that we're afraid will accelerate. The last time a large ice sheet melted sea level went up at a rate of five meters per century. That's one meter every 20 years. And that is a kind of sea level rise, a rate which the simple ice sheet models available now just cannot produce because they don't have the physics in them to give you the rapid collapse that happens in a very nonlinear system ("Gorilla of Sea Level Rise").

Larsen BIn "A Worrying Trend of Less Ice, Higher Seas," published in the March 24, 2006, issue of Science, Richard A. Kerr, explained that the melting of the ice sheets and glaciers in Greenland and Antarctica has accelerated in the last ten years. Ice shelves are moving rapidly toward the sea and melting. For example, when the 1,255-square-mile Larsen B ice shelf broke off of Antarctica in 2002, it only took 35 days for it to disappear.

In part, the critique offered by Hansen and other leading climatologists of the new IPCC report stems from the urgency of the matter at hand. "We have," Hansen says, "at most ten years -- not ten years to decide upon action, but ten years to alter fundamentally the trajectory of global greenhouse emissions" -- if we are to prevent such disastrous outcomes from becoming inevitable ("The Threat to the Planet," New York Review of Books, July 13, 2006). One crucial decade, in other words, separates us from irreversible, nonlinear processes that could set in motion the conditions for an entirely new geological age leading to the extinction of a majority of species on the earth and threatening human civilization.


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