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Even with exaggerated assumptions of sensitivity, the IPCC has to down-grade alarm

The United Nations’ Intergovernmental Panel on Climate Change
will shortly publish the second part of its latest report, on the
likely impact of climate change. Government representatives are
meeting with scientists in Japan to sex up—sorry, rewrite—a summary
of the scientists’ accounts of storms, droughts and diseases to
come. But the actual report, known as AR5-WGII, is less frightening than its predecessor seven
years ago.

The 2007 report was riddled with errors about Himalayan
glaciers, the Amazon rain forest, African agriculture, water
shortages and other matters, all of which erred in the direction of
alarm. This led to a critical appraisal of the report-writing
process from a council of national science academies, some of whose
recommendations were simply ignored.

Others, however, hit home. According to leaks, this time the
full report is much more cautious and vague about
worsening cyclones, changes in rainfall, climate-change refugees,
and the overall cost of global warming.

It puts the overall cost at less than 2% of GDP for a 2.5
degrees Centigrade (or 4.5 degrees Fahrenheit) temperature increase
during this century. This is vastly less than the much heralded
prediction of Lord Stern, who said climate change would cost 5%-20%
of world GDP in his influential 2006 report for the British

The forthcoming report apparently admits that climate change has
extinguished no species so far and expresses “very little
confidence” that it will do so. There is new emphasis that climate
change is not the only environmental problem that matters and on
adapting to it rather than preventing it. Yet the report still
assumes 70% more warming by the last decades of this century than
the best science now suggests. This is because of an overreliance
on models rather than on data in the first section of the IPCC
report—on physical science—that was published in September

In this space on Dec. 19, 2012, I forecast that the IPCC was
going to have to lower its estimates of future warming because of
new sensitivity results. (Sensitivity is the amount of warming due
to a doubling of atmospheric carbon dioxide.) “Cooling Down Fears of Climate Change” (Dec.
19), led to a storm of protest, in which I was called
“anti-science,” a “denier” and worse.

The IPCC’s September 2013 report abandoned any attempt to
estimate the most likely “sensitivity” of the climate to a doubling
of atmospheric carbon dioxide. The explanation, buried in a
technical summary not published until January, is that “estimates
derived from observed climate change tend to best fit the observed
surface and ocean warming for [sensitivity] values in the lower
part of the likely range.” Translation: The data suggest we
probably face less warming than the models indicate, but we would
rather not say so.

The Global Warming Policy Foundation, a London think tank,
published a careful survey of all the reliable studies
of sensitivity on March 5. The authors are British climate
scientist Nic Lewis (who has no academic affiliation but a growing
reputation since he discovered a glaring statistical distortion
that exaggerated climate sensitivity in the previous IPCC report)
and the Dutch science writer Marcel Crok. They say the IPCC’s
September report “buried good news about global warming,” and that
“the best observational evidence indicates our climate is
considerably less sensitive to greenhouse gases than climate
scientists had previously thought.”

Messrs. Lewis and Crok argue that the average of the best
observationally based studies shows the amount of immediate warming
to be expected if carbon dioxide levels double after 70 years is
“likely” to be between one and two degrees Centigrade, with a best
estimate of 1.35C (or 2.4F). That’s much lower than the IPCC
assumes in its forthcoming report.

In short, the warming we experienced over the past 35
years—about 0.4C (or 0.7F) if you average the measurements made by
satellites and those made by ground stations—is likely to continue
at about the same rate: a little over a degree a century.

Briefly during the 1990s there did seem to be warming that went
as fast as the models wanted. But for the past 15-17 years there
has been essentially no net warming (a “hiatus” now conceded by the
IPCC), a fact that the models did not predict and now struggle to
explain. The favorite post-hoc explanation is that because of
natural variability in ocean currents more heat has been slipping
into the ocean since 2000—although the evidence for this is far
from conclusive.

None of this contradicts basic physics. Doubling carbon dioxide
cannot on its own generate more than about 1.1C (2F) of warming,
however long it takes. All the putative warming above that level
would come from amplifying factors, chiefly related to water vapor
and clouds. The net effect of these factors is the subject of
contentious debate.

In climate science, the real debate has never been between
“deniers” and the rest, but between “lukewarmers,” who think
man-made climate change is real but fairly harmless, and those who
think the future is alarming. Scientists like Judith Curry of the
Georgia Institute of Technology and Richard Lindzen of MIT have
moved steadily toward lukewarm views in recent years.

Even with its too-high, too-fast assumptions, the recently
leaked draft of the IPCC impacts report makes clear that when it
comes to the effect on human welfare, “for most economic sectors,
the impact of climate change will be small relative to the impacts
of other drivers,” such as economic growth and technology, for the
rest of this century. If temperatures change by about 1C degrees
between now and 2090, as Mr. Lewis calculates, then the effects
will be even smaller.

Indeed, a small amount of warming spread over a long period
will, most experts think, bring net improvements to human welfare.
Studies such as by the IPCC author and economist Professor Richard
Tol of Sussex University in Britain show that global warming has
probably done so already. People can adapt to such change—which
essentially means capture the benefits but minimize the harm.
Satellites have recorded a roughly 14% increase in greenery on the
planet over the past 30 years, in all types of ecosystems, partly
as a result of man-made CO2 emissions, which enable plants to grow
faster and use less water.

There remains a risk that the latest science is wrong and rapid
warming will occur with disastrous consequences. And if renewable
energy had proved by now to be cheap, clean and thrifty in its use
of land, then we would be right to address that small risk of a
large catastrophe by rushing to replace fossil fuels with
first-generation wind, solar and bioenergy. But since these forms
of energy have proved expensive, environmentally damaging and
land-hungry, it appears that in our efforts to combat warming we
may have been taking the economic equivalent of chemotherapy for a

Almost every global environmental scare of the past half century
proved exaggerated including the population “bomb,” pesticides,
acid rain, the ozone hole, falling sperm counts, genetically
engineered crops and killer bees. In every case, institutional
scientists gained a lot of funding from the scare and then quietly
converged on the view that the problem was much more moderate than
the extreme voices had argued. Global warming is no different.

By Matt Ridley | Tagged:  rational-optimist  wall-street-journal