My article in the Review section of the Wall
Street Journal:
Later this month, a long-awaited event that last happened in
2007 will recur. Like a returning comet, it will be taken to
portend ominous happenings. I refer to the Intergovernmental Panel
on Climate Change’s (IPCC) “fifth assessment report,” part of which
will be published on Sept. 27.
There have already been leaks from this 31-page document, which
summarizes 1,914 pages of scientific discussion, but thanks to a
senior climate scientist, I have had a glimpse of the key
prediction at the heart of the document. The big news is that, for
the first time since these reports started coming out in 1990, the
new one dials back the alarm. It states that the temperature rise
we can expect as a result of man-made emissions of carbon dioxide
is lower than the IPPC thought in 2007.
Admittedly, the change is small, and because of changing
definitions, it is not easy to compare the two reports, but retreat
it is. It is significant because it points to the very real
possibility that, over the next several generations, the overall
effect of climate change will be positive for humankind and the
planet.
Specifically, the draft report says that “equilibrium climate
sensitivity” (ECS)—eventual warming induced by a doubling of carbon
dioxide in the atmosphere, which takes hundreds of years to
occur—is “extremely likely” to be above 1 degree Celsius (1.8
degrees Fahrenheit), “likely” to be above 1.5 degrees Celsius (2.4
degrees Fahrenheit) and “very likely” to be below 6 degrees Celsius
(10.8 Fahrenheit). In 2007, the IPPC said it was “likely” to be
above 2 degrees Celsius and “very likely” to be above 1.5 degrees,
with no upper limit. Since “extremely” and “very” have specific and
different statistical meanings here, comparison is difficult.
Still, the downward movement since 2007 is clear, especially at
the bottom of the “likely” range. The most probable value (3
degrees Celsius last time) is for some reason not stated this
time.
A more immediately relevant measure of likely warming has also
come down: “transient climate response” (TCR)—the actual
temperature change expected from a doubling of carbon dioxide about
70 years from now, without the delayed effects that come in the
next century. The new report will say that this change is “likely”
to be 1 to 2.5 degrees Celsius and “extremely unlikely” to be
greater than 3 degrees. This again is lower than when last
estimated in 2007 (“very likely” warming of 1 to 3 degrees Celsius,
based on models, or 1 to 3.5 degrees, based on observational
studies).
Most experts believe that warming of less than 2 degrees Celsius
from preindustrial levels will result in no net economic and
ecological damage. Therefore, the new report is effectively saying
(based on the middle of the range of the IPCC’s emissions
scenarios) that there is a better than 50-50 chance that by 2083,
the benefits of climate change will still outweigh the harm.
Warming of up to 1.2 degrees Celsius over the next 70 years (0.8
degrees have already occurred), most of which is predicted to
happen in cold areas in winter and at night, would extend the range
of farming further north, improve crop yields, slightly increase
rainfall (especially in arid areas), enhance forest growth and cut
winter deaths (which far exceed summer deaths in most places).
Increased carbon dioxide levels also have caused and will continue
to cause an increase in the growth rates of crops and the greening
of the Earth—because plants grow faster and need less water when
carbon dioxide concentrations are higher.
Up to two degrees of warming, these benefits will generally
outweigh the harmful effects, such as more extreme weather or rising sea levels, which
even the IPCC concedes will be only about 1 to 3 feet during this
period.
Yet these latest IPCC estimates of climate sensitivity may still
be too high. They don’t adequately reflect the latest rash of
published papers estimating “equilibrium climate sensitivity” and
“transient climate response” on the basis of observations, most of
which are pointing to an even milder warming. This was already
apparent last year with two papers—by scientists at the University of Illinois and Oslo University in Norway—finding a lower ECS
than assumed by the models. Since then, three new papers conclude
that ECS is well below the range assumed in the models. The most
significant of these, published in Nature Geoscience by a team
including 14 lead authors of the forthcoming IPCC scientific
report, concluded that “the most likely value of equilibrium
climate sensitivity based on the energy budget of the most recent
decade is 2.0 degrees Celsius.”
Two recent papers (one in the Journal of the American Meteorological
Society, the other in the journal Earth System Dynamics) estimate that TCR is
probably around 1.65 degrees Celsius. That’s uncannily close to the
estimate of 1.67 degrees reached in 1938 by Guy Callendar, a
British engineer and pioneer student of the greenhouse effect. A
Canadian mathematician and blogger named Steve McIntyre has pointed out that Callendar’s model does a
better job of forecasting the temperature of the world between 1938
and now than do modern models that “hindcast” the same data.
The significance of this is that Callendar assumed that carbon
dioxide acts alone, whereas the modern models all assume that its
effect is amplified by water vapor. There is not much doubt about
the amount of warming that carbon dioxide can cause. There is much more doubt about whether net
amplification by water vapor happens in practice or is offset by
precipitation and a cooling effect of clouds.
Since the last IPCC report in 2007, much has changed. It is now
more than 15 years since global average temperature rose
significantly. Indeed, the IPCC chairman Rajendra Pachauri has
conceded that the “pause” already may have lasted for 17 years,
depending on which data set you look at. A recent study in Nature Climate Change by
Francis Zwiers and colleagues of the University of Victoria,
British Columbia, found that models have overestimated warming by
100% over the past 20 years.
Explaining this failure is now a cottage industry in climate
science. At first, it was hoped that an underestimate of sulfate
pollution from industry (which can cool the air by reflecting heat
back into space) might explain the pause, but the science has gone
the other way—reducing its estimate of sulfate cooling. Now a
favorite explanation is that the heat is hiding in the deep ocean.
Yet the data to support this thesis come from
ocean buoys and deal in hundredths of a degree of temperature
change, with a measurement error far larger than that. Moreover,
ocean heat uptake has been slowing over the past eight years.
The most plausible explanation of the pause is simply that
climate sensitivity was overestimated in the models because of
faulty assumptions about net amplification through water-vapor
feedback. This will be a topic of heated debate at the political
session to rewrite the report in Stockholm, starting on Sept. 23,
at which issues other than the actual science of climate change
will be at stake.
Post-script:
On a blog called Desmog Blog, John Abraham has criticized my
recent article in the Wall Street Journal on climate sensitivity.
Here’s my piece
http://online.wsj.com/article/SB10001424127887324549004579067532485712464.html
And here’s his piece:
http://www.desmogblog.com/2013/09/16/john-abraham-slams-matt-ridley-climate-denial-op-ed-wall-street-journal.
It’s a poor response, characterized by inaccurate representation
of what I said, even down to actual misquoting. In the whole
article, he puts just five words in quotation marks as written by
me, yet in doing so he misses out a whole word: 17% of the
quotation. Remarkable. If I did that, I would be very
embarrassed.
He directly contradicts the IPCC’s report on extreme weather,
which found no link between current storms and man-made climate
change; he is apparently unaware that the rising costs of extreme
weather are entirely caused by rising investment and insurance
values, not rising quantities of extreme weather, as even a small
amount of research would have told him (
http://rogerpielkejr.blogspot.co.uk/2013/08/follow-up-q-from-senate-epw.html);
he falsely claims that I say rising sea levels will be beneficial,
when I wrote no such thing; and he wholly ignores the benefits of
mild climate change, even though I was careful to say that the key
thing is to compare costs and benefits. It is possible that he does
not know the meaning of the word “net”: he certainly shows no
understanding of the concept.
“General
statements about extremes are almost nowhere to be found in the
literature but seem to abound in the popular media,” said
climate scientist Gavin Schmidt of the NASA Goddard Institute for
Space Studies recently. “It’s this popular perception that global
warming means all extremes have to increase all the time, even
though if anyone thinks about that for 10 seconds they realize
that’s nonsense.”
Mr Abraham’s main point is that up to 2 degrees C of
warming is likely to do net harm. For this surprising claim, he
produces no evidence. None. The evidence suggest the opposite –
that less than two degrees of warming will cut excess winter
deaths, increase average rainfall, extend growing seasons and
increase rates of photosynthesis in wild and agricultural
ecosystems. “A global warming of less than 2.5°C could
have no significant effect on overall food production,” says the
UNFCC website.
http://unfccc.int/essential_background/background_publications_htmlpdf/climate_change_information_kit/items/288.php
See links here
http://www.sciencedirect.com/science/article/pii/S0165188913000092%00
and here:
http://wattsupwiththat.com/2010/01/06/winter-kills-excess-deaths-in-the-winter-months/.
And yet it is he who accuses me of “non-science nonsense”. It’s
truly disgraceful that a tenured academic, as I assume Mr Abraham
to be, should make so many mistakes and yet feel free to hurl
unsubstantiated abuse at another human being, however desperate he
may be. In writing about climate change I am careful not to make
unprovoked ad-hominem attacks – until attacked in this way. I
always play the ball, not the man. Mr Abraham, if he wishes to be
taken seriously, should try to do likewise.
Second post-script: I now see there’s another attack on my
article written by Joe Romm at ThinkProgress. It’s a bizarre rant
that completely mischaracterises my article, for example in saying
that I accept a 2C “target” and that I mischaracterise the Ring et
al paper, which I don’t: I accurately report its low sensitivity
finding. Do people like Romm really think that this sort of
straw-man attack is persuasive? The way in which he avoids my main
argument only makes me more convinced that I have a point.