Climate Change Science?
National Academy of Sciences Global Warming Report Fails to Live
Up to Its Billing
by Gerald Marsh
"Greenhouse gases are accumulating
in Earth's atmosphere as a result of human activities, causing
surface air temperatures and subsurface ocean temperatures to
Thus begins the summary of the June 2001
National Academy of Sciences report "Climate Change Science,"
which made headlines across the world for (supposedly) providing
additional "proof" that mankind is causing global warming.
But the headline writers didn't read
the fine print.
This often quoted, categorical statement
is not supported by the rest of the NAS report - or the scientific
report of Working Group I of the Intergovernmental Panel on Climate
Change (IPCC), the United Nations body frequently cited as a
key authority on global warming.
Two sentences later in the NAS summary,
readers are told that "The changes observed over the last
several decades are likely mostly due to human activities, but
we cannot rule out that some significant part of these changes
are also a reflection of natural variability." "Likely
mostly due to human activities"? "Some significant
part"? Given these qualifications, and the very large uncertainties
in the science, how could the National Research Council (NRC)
- the research arm of the NAS - approve such a categorical opening
The NAS report is a summary rather than
a critical review of the IPCC reports. It was prepared and approved
in less than a month after the White House submitted its formal
request. NRC reports, to quote Richard Lewontin of Harvard University,
"always speak with one voice. Such reports... can produce
only a slight rocking of the extremely well gyrostabilized ship
of state, no matter how high the winds and waves. Any member
of the crew who mutinies is put off at the first port of call."1 In
other words, there is a forced consensus, one that tends to provide
an oversimplified picture of the state of scientific research
and of the uncertainties.
One must dig carefully through the report
to discover that water vapor and cloud droplets are in fact the
dominant cause of greenhouse warming. We are not told, however,
what fraction of the greenhouse effect is due to water vapor
and clouds.2 Nor are we told that carbon dioxide is a minor
greenhouse gas - one that accounts for less than ten percent
of the greenhouse effect - whose ability to absorb heat is quite
limited.3 Adding more carbon dioxide to the atmosphere
only increases greenhouse warming very slowly. Similarly, decreasing
the amount of carbon dioxide in the atmosphere only decreases
greenhouse warming very slowly.
Thus, the relatively small changes in
the emission of carbon dioxide agreed to in the Kyoto Protocol
would have an insignificant impact on global warming. The provisions
of the Protocol seem singularly innocent of this fact.
The NAS study also notes that increased
radiation from the sun could be responsible for a significant
part of climate change during part of the industrial era. But
the study does not tell us that the warming due to the increase
in solar output4 is comparable to that alleged to be a consequence
of the 25% rise in atmospheric carbon dioxide concentration since
the end of the 18th century. Because carbon dioxide is a minor
greenhouse gas, and increased carbon dioxide concentration in
the atmosphere does not proportionately increase its greenhouse
effect, this rise has had only a minimal impact on the earth's
Most people assume that the rise in atmospheric
carbon dioxide is due to human activity. However, our understanding
of the carbon cycle is so poor that we cannot be certain this
is the case.5 Nonetheless, deforestation and the burning of
fossil fuels (which, on a yearly basis, comprises only some three-and-a-half
percent of the two-way exchange of carbon between the earth and
its atmosphere), most likely does contribute to the increased
concentration of this gas.
In 1976, when the earth had been cooling
for some three decades, "mainstream scientists" believed
that we were sliding into a new ice age. There has been significant
improvement in modeling the ocean and atmosphere since then,
but the predictions of these models still do not form a sound
basis for public policy decisions. As put by Ahilleas Maurellis
of the Space Research Organization Netherlands, "Until we
understand the full picture, perhaps the best reaction to global
warming is for everybody to just keep their cool."6
# # #
Gerald Marsh, a physicist,
is a member of the National Advisory Board of The National Center
for Public Policy Research. He served with the U.S. START delegation
and was a consultant to the Office of the Chief of Naval Operations
on strategic nuclear policy and technology for many years. He
is on the Editorial board of the Bulletin of the Atomic Scientists.
Comments may be sent to [email protected].
1 Richard Lewontin, "Genes in the Food!,"
New York Review of Books, June 21, 2001.
2 J. T. Houghton, et al., eds, Climate Change: The IPCC
Scientific Assessment, Cambridge University Press, Cambridge,
1991. Notice that the IPCC estimate of 60-70% is for a clear
sky, thereby neglecting the contribution from water vapor in
clouds. The clear sky greenhouse effect, measured in watts per
square meter is 146 w/m2; clouds contribute an additional 33
w/m2 to the clear-sky value, an increase of 23% over the IPCC
estimate. See also M. Z. Jacobson, Fundamentals of Atmospheric
Modeling, Cambridge University Press, Cambridge, 1999.
3 Houghton, et. al., Section 2.2.2.
4 A. Eddy, Science 192, 1189, 1976; E. N. Parker, Nature
399, 416, 1999; E. W. Cliver, et al., Geophysical Research Letters
25, 1035, 1998; T. J. Crowley and K. Y. Kim, Geophysical Research
Letters 23, 359, 1996; G. C. Reid, Journal of Geophysical Research
96, 2835, 1990; E. Friis-Christensen and K. Lassen, Science 254,
698, 1991; J. Lean, et al., Geophysical Research Letters 22,
3195, 1995 and R. A. Kerr, Science 271, 1360, 1996.
5 W. M. Post, et al., "The Global Carbon Cycle,"
American Scientist 78, 310, 1990.
6 Ahilleas Maurellis, Physics World, February 2001.