Is the New UN Global Warming Report Too Conservative?

There is now a strong consensus among climate scientists that human activities are the primary forces responsible for the observed warming of the earth’s atmosphere.  The recently released fourth assessment report, Climate Change 2007: The Physical Science Basis, of the United Nations Intergovernmental Panel on Climate Change (IPCC) notes that warming is “unequivocal” and human activities are the cause.  Global average temperature has risen by 0.74°C (1.3°F) since 1906.  The IPCC projects a further increase of 0.4°C (0.7°F) in warming during the next two decades, and an increase (best estimate) of 1.8-4.0°C (3.3-7.1°F) in global average temperature during this century.

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,”  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.

As the temperature increases, a chain reaction is set in motion, amplifying warming tendencies.  The ice caps melt and pools of water are formed.  Rather than reflecting solar radiation, like the white ice does, the blue water absorbs the heat, further accelerating the rate of melting of the adjacent ice cap.  This water also heats the ice below, driving deep holes of warm water within an ice shelf.  The water from melting ice over land, such as in Antarctica and Greenland, sinks deep into the ice, cutting tunnels, known as “moulins.”  When it reaches the land beneath the ice, it both warms the ice underneath and serves as a lubricant that could lead massive amounts of ice to shift and fall into the sea.  The melting of just Greenland’s ice sheet could raise the worldwide sea level 20 feet.  These positive feedback loops can start out slow, but accelerate in time.

In contemplating such changes and increases in the global temperature, James Hansen points out “if you start talking two or three degrees Celsius, then you’re really talking about a different planet from the one we know” (“Gagged Climate Expert,” Living on Earth, February 3, 2006).

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.

The severity of the situation is amplified if we consider the full range of ecological consequences (droughts, flooding, severe storms, loss of biodiversity, etc.) of global climate change, not to mention the array of environmental problems that are emerging as every ecosystem is threatened with collapse.  The scale of ecological destruction — as well as the ongoing nuclear threat — caused the Bulletin of Atomic Scientists recently to move its symbolic “doomsday clock” to five minutes to midnight, two minutes forward from where it was — and twelve minutes closer to cataclysm than in the early 1990s.

In reality, the threat to the planet from the environmental crisis is even more serious than natural-scientific reports suggest (see “Ecology of Destruction,” Monthly Review, February 2007).  This is because there is much more than mere political inertia, as commonly supposed, preventing the world from radically changing course and initiating an alternative scenario to business as usual.  Capitalism is by its very nature an unceasing treadmill of production.  As Karl Marx put it in the nineteenth century: “The division of labor is necessarily followed by greater division of labor, the application of machinery by still greater application of machinery, works on a large scale by work on a still larger scale.  That is the law [driven by competition] which again and again throws bourgeois production out of its old course and which compels capital to intensify the productive forces of labor, because it has intensified them . . . the law which gives capital no rest and continually whispers in its ear ‘Go on!  Go on!'” (Wage Labor and Capital).  There is no conceivable alternative scenario within such a runaway-train system that leads toward a sustainable relation to the environment, much less a just society.  What is needed is nothing less than a worldwide revolution in our relation to nature, and thus of global society itself.

Brett Clark is a frequent contributor to Monthly Review.  He has also published articles in Organization & Environment, Theory and Society, and the Sociological Quarterly.  John Bellamy Foster is professor of sociology at the University of Oregon, author of Marx’s Ecology, Ecology against Capitalism, The Vulnerable Planet, and Naked Imperialism, and editor of Monthly Review.

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