(The author is a Reuters market analyst. The views expressed
are his own.)
By Gerard Wynn
LONDON, June 21 A major recent study has put the
cat among the pigeons on climate change, challenging the size of
the problem in the near-term and the role of a recent slowdown
The paper, published in the journal Nature Geoscience in
May, involved scientists from 14 institutions and calculated
that more extreme climate change was now less likely, after
taking into account slower warming in the past decade.
The notion of changing a view as a result of a single decade
of observations is somewhat controversial, given that natural
patterns can span several decades.
And the paper applied a method for estimating future climate
change which is known to produce lower warming estimates than a
corrsponding measure used by the U.N. climate panel, the
Intergovernmental Panel on Climate Change (IPCC) and the
International Energy Agency (IEA).
Either way, the big picture is the same: the Earth is
warming up because of manmade greenhouse gas emissions.
But the more uncertain the science is over the scale of
warming, the less political will there may be.
This is at a time when U.N. climate negotiations have
floundered, the U.S. congress is reluctant to act, and arguably
sceptics playing to the consumer cost of low-carbon energy have
gained more traction at the grassroots level than environmental
The science, for its part, reflects a vastly complicated
climate system and the number of variables at play, although
there is some hope that new research plus observed warming may
resolve some uncertainties by the end of the decade.
The new paper's key conclusion, at least politically, is
that it forecasts the long-term impact of a doubling of CO2
levels on the earth at 2 degrees of warming.
Actual warming may be more, depending on the net effect of
other greenhouse gases and pollution.
The estimate of 2 degrees is lower than the IPCC estimate by
a whole degree and, interestingly enough, precisely in line with
the maximum safety limit that every climate conference for the
past five years has put on warming.
A common benchmark that scientists use to quantify the
climate problem is the amount of warming expected from a
doubling of carbon dioxide levels in the atmosphere.
That includes two related measures.
One is the short-term warming at the moment CO2 levels reach
double their baseline levels, called the transient climate
The other is the "equilibrium climate sensitivity" (ECS), or
temperature change after the Earth has fully responded centuries
later to the same doubling in CO2.
There are several ways to estimate them.
One approach uses complex computer models to imitate the
planet's entire climate system using general circulation models
based on our knowledge of atmospheric and ocean physics.
The models are calibrated to try and reproduce the observed
climate over the temperature record of the past 150 years, and
then simulate future climate change as a result of rising CO2.
An alternative approach is based on an estimate of the
Earth's "energy budget".
It starts with the observed temperature change at the
Earth's surface, and then takes into account other factors which
may brake surface warming, such as the uptake of heat by the
It, too, uses computer models to estimate other influences
such as from manmade pollution, which can cool the Earth.
A computer simulation approach may capture vital unseen
influences on the Earth's climate and so be more nuanced.
By incorporating recent temperature observations, the energy
budget approach is more up to date.
It is hard to say which is more accurate.
Last month's paper - "Energy budget constraints on climate
response" - used an energy budget approach, and found that by
focusing on the most recent decade of temperature observations
it could rule out more extreme warming in their calculated
ranges for ECS and TCR.
The authors accounted not only for lower surface temperature
in the last decade, but also a rapid build up of heat in the
"Recent observations suggest the expected rate of warming in
response to rising greenhouse gas levels ... is likely to lie
within the range of current climate models, but not at the high
end of this range," said lead author Alexander Otto.
The finding that the top end of the temperature range can
now be eliminated is perhaps not especially surprising.
First, warming has slowed compared with the 1980s and 1990s.
Second, it is to be expected that extreme warming values
could be revised downwards: upper estimates are open-ended and
speculative while lower estimates are limited by warming that we
know has already happened, at 0.8 degrees Celsius since the
The more interesting result is that the paper using the
energy budget approach estimated less warming than a computer
simulation relying less on current observation.
The different results have something to do with, first, the
uncertain impact of natural variation in driving climate
changes, and second, the uncertain role of changing cloud cover;
heat uptake in the deep oceans; and manmade pollution which can
cool the Earth.
Scientists take comfort at least that the two methods
produce results in the same range.
The short-term TCR is more relevant - because this is
warming that we will see this century, and it makes less heroic
assumptions about how people will keep a lid on further
emissions in future centuries.
At present emissions rates, CO2 levels will reach double
pre-industrial levels at some point in the second half of the
At that point warming should therefore reach the level
estimated using the TCR measure, plus any extra warming from
other greenhouse gases.
The recent article has a best estimate for TCR of about 1.3
degrees versus 1.8 degrees Celsius using a computer simulation
approach. ("Global warming under old and new scenarios using
IPCC climate sensitivity range estimates", February 2012)
Repeated communiques from U.N. climate conferences have
warned that 2 degrees warming compared with pre-industrial
temperatures is manageable, but no more.
Scientists are saying that we are on track to reach that
level of warming this century, or perhaps not.
Climate change is clearly serious, given hugely costly and
possibly irreversible risks such as sea level rise and deadly
droughts and floods.
And neither scientific approach accounts for the possibility
of climate tipping points, such as the sudden release of
greenhouse gases from the sea bed as a result of warming oceans.
But the science shows a complicated problem which is hard to
pin down, and is therefore struggling to engage voters. And the
more cracks appear in the consensus that climate change demands
urgent action, the less political will there will be to do more.
(Reporting by Gerard Wynn; editing by Patrick Graham)