A summary of the United Nations Intergovernmental Panel on
Climate Change Fourth Assessment Report (IPCC Report) was released
on February 2, and many in the media and Congress are citing it as
further evidence that global warming is a dire threat. The full
report, with accompanying scientific assessment and detailed
assumptions, will not be released for several months. However,
caution is warranted in drawing policy conclusions based on this
summary, as the full scientific debate over the IPCC report has not
begun. And while the summary strongly emphasizes mankind's role in
global warming, it has retreated on a number of important
assertions from past reports.
Just a Summary
It should be emphasized that only a short "Summary for
Policymakers" has been released, not the actual report which
contains the underlying scientific assessment. The final version of
the full report is scheduled to come out later this year. IPCC
summaries are written at the direction of political appointees
representing member nations. The limitations and potential biases
of such summaries give reason to withhold judgment until the
scientists actually weigh in--both the IPCC scientists and
especially the independent scientists who will comment on the final
report. That the summary is being so aggressively marketed ahead of
the science is itself reason for caution.
That said, the summary is the only thing most journalists and
politicians read, and the finding that has received the most
attention is that the IPCC is now more certain than in its 2001
report that mankind has contributed to global warming since 1750.
In truth, few so-called skeptics dispute that there has been some
human contribution, so the fact that the summary says the
likelihood is 90 percent or more is not as newsworthy as it first
appears. This upward revision in the certainty that mankind has
impacted the climate should not be confused with an upward revision
in the predictions of consequent harm.
The more important questions have always been the extent of
warming, the seriousness of the consequences, and what responsive
policies make sense.
The summary includes a wide range of assumptions and outcomes,
and thus it is hard to generalize about its predictions. However,
it does appear that estimates of future sea level rise--likely the
greatest concern from warming--are being revised downward.
Estimates range from 0.18 to 0.59 meters (about 7 to 23 inches)
over the course of a century, about a third lower than in the
previous report and well below popular fears of 20 feet or
Again it is still too early to speculate what the final
scientific assessment will say (and how well it will hold up to
scrutiny), but the summary does appear to have backtracked on other
points as well. For example, the last IPCC report emphasized the
so-called "hockey stick" notion that earth's temperature was
relatively stable for a thousand years (the shaft of the hockey
stick) and then shot up in an unprecedented manner in the 20th
century (the blade). Thus, the previous IPCC report discounted the
Medieval Warm Period and subsequent Little Ice Age, implying that
current temperature increases are not due to natural variability.
The hockey stick (and its conclusion that current temperatures are
unprecedented throughout most of recorded history) has come under
scientific attack in recent years, and based on the new summary, it
appears that the IPCC has deemphasized it. How the deletion of the
hockey stick from the upcoming report squares with IPCC's claims of
increased certainty over mankind's impact on climate will be a
significant source of contention.
On the question of whether global warming contributes to
powerful hurricanes like Katrina, the summary hedges quite a bit,
calling the hurricane-warming link "more likely than not" rather
than "very likely" or "likely," as used elsewhere in the summary.
The summary concedes in a footnote that the magnitude of mankind's
contribution was not assessed and that the attribution was based
"on expert judgment" and not formal studies. Again, depending on
what the final report says, activists and politicians who
unequivocally blamed Katrina's devastation on global warming may
have to back off.
Is a Kyoto-Like Solution Wise?
Whatever the risks of global warming identified in the IPCC
Report, global warming policies also carry risks--especially those
policies that emphasize energy rationing as a solution. Separate
from the scientific discussion sparked by the IPCC Report is the
discussion about the appropriate response and, in particular, the
actual merits of a costly program to cap carbon dioxide emissions
from fossil fuel use. This was the approach taken in the Kyoto
Protocol, the multilateral treaty to address global warming. Kyoto
is proving so prohibitively expensive that most of the developed
nations that have signed onto it (Western Europe, Canada, Japan,
but not the United States) have little hope of meeting its looming
targets. The economic burdens of Kyoto, especially on
already-stagnant economies, have proven unacceptable.
Estimates of the cost for U.S. compliance ranged from $100 to
$400 billion dollars annually--enough to have a serious impact on
employment and economic growth. America wisely rejected this
approach. And even assuming the IPCC is right, the Kyoto Protocol
would only avert 0.07 degrees Celsius of warming by 2050, an amount
too small too measure.
The economic damage of energy rationing to developing nations
would be severe, strangling growth and imposing hardships on
billions who are already barely subsisting. It would also slow the
spread of electrification to the nearly 2 billion who do not yet
have it. On the other hand, exempting developing nations from any
Kyoto-style requirements means that carbon emissions will continue
to increase regardless of what the developed world does.
Science should play a big role in global warming policy, and the
full IPCC Report should be a part of that. But economics must also
play a role, lest the U.S. embark on a course that does more harm
Lieberman is Senior Policy Analyst in the Thomas A. Roe
Institute for Economic Policy Studies at The Heritage