Is the New UN Global Warming Report Too Conservative?

by Brett Clark and John Bellamy Foster

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 0.74C (1.3F) since 
1906.  The IPCC projects a further increase of 
0.4C (0.7F) in warming during the next two 
decades, and an increase (best estimate) of 
1.8-4.0C (3.3-7.1F) 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 

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 3C (5.4F) 
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 1C (1.8F) 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 2-3C (3.6-5.4F) 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 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, 

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 

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 

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 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.