Scientists take the Mail on Sunday to task over claim that warming is half what IPCC said last time
- 16 Sep 2013, 15:40
- Roz Pidcock
The Mail on Sunday yesterday claimed the international climate
community is conceding the world hasn't warmed as much since the
middle of last century as previously thought. We ask climate
scientists what they make of the story.
A major new report on the state of the climate is due imminently
from the Intergovernmental Panel on Climate Change (IPCC). An involved process of review
by experts and governments worldwide is coming to a close, and the
first part of the
report is set for release at the end of next week.
Last week, a draft summary of the document was
journalists. In yesterday's Mail on Sunday, climate skeptic
journalist David Rose claims to have seen information in the
summary which "reveals scientific forecasts of imminent doom were
The Mail on Sunday
piece is entitled 'World's top climate scientists confess:
Global warming is just HALF what we said'. It follows a series of
articles Rose has written for the Mail on Sunday recently
which, taken together, suggest that the fundamentals of climate
science are being thrown into doubt.
Telegraph quickly repurposed the Mail on Sunday article under
the headline, 'Top climate scientists admit global warming
forecasts were wrong'. Meanwhile,
The Australian went a step further with a story headlined 'We
got it wrong on warming, says IPCC'.
Rate of warming not halved
The Mail on Sunday gives the story a generous double page
spread, and repeats many of the same arguments Rose has made in
pieces. So let's focus on what's new - the central claim of the
article that scientists have cut their assessment of warming since
the middle of last century by half.
The Mail on Sunday says:
"Back [in 2007], [the IPCC] said that
the planet was warming at a rate of 0.2 degrees Celsius every
decade … But the new report says the true figure since 1951 has
been only 0.12 Celsius per decade - a rate far below even the
lowest computer prediction"
Dr Richard Allan, a climate scientist at the University of
Reading, tells us this statement is quite simply wrong. He says
Rose has mixed up the numbers in the last IPCC report.
"The main claim by David Rose in the
Mail on Sunday is that rate of global warming since 1951 has been
halved since the last IPCC report. This is completely
In 2007, the IPCC said the rate of warming since 1951 had been
not 0.2 but
0.13 degrees Celsius per decade. If the new report says 0.12
degrees Celsius, as the Mail on Sunday suggests, this is a very
minor revision of 0.01 degrees.
Professor Myles Allen from Oxford University, who is quoted
pretty heavily in the piece, posted a comment below the
article pointing out Rose's error. He said:
"Neither the IPCC in 2007 nor the
current crop of climate models ever suggested that the world has
been, or should have been, warming at 0.2 degrees per decade since
1951. So the headline should have been "Global warming is just 92
percent of what we said it was", on an apples-for-apples
And Dr Ed Hawkins, a climate scientist at Reading University,
"The trend over the past 50 years [the
Mail on Sunday] says is in [the new IPCC report] is almost
identical to the [last report in 2007] so the article's headline
and premise that global warming is half of what was said ... is
So where does the 0.2 degree per decade figure come from?
Richard Allan tells us it does appear in the last IPCC report, but
refers to a 15-year period in the run up to the report's release,
not the warming per decade since 1951. He says:
"The 0.2 degrees Celsius per decade
figure relates to an observed warming over the period 1990-2005
which clearly cannot be compared with the period since 1951".
So the two figures Rose compares are not measuring the same
thing. As the Met Office's Richard Betts tweeted
yesterday: "Rose created a headline by misrepresenting [the 2007
The Mail on Sunday's error has led one or two other journalists
astray, and resulted in some fairly confused media coverage.
Telegraph appears to have repeated the Mail on Sunday story
wholesale. But the paper was forced to make a swift correction
yesterday after suggesting the 2007 IPCC report claimed warming
since 1951 had been 1.3 degrees per decade - ten times the actual
This was quickly changed online to the correct figure of 0.13
degrees per decade. The change is likely to leave readers confused
by what the article is actually claiming, as it now reads:
"The "summary for policymakers" of the
report, seen by the Mail on
Sunday, states that the world is warming at a rate of 0.12
degrees Celsius per decade since 1951, compared to a prediction of
0.13 degrees Celsius per decade in their last assessment published
As Richard Allan tells Carbon Brief:
"That's 0.01 degrees Celsius per decade
difference, which makes the title [Top climate scientists admit
global warming forecasts were wrong] seem completely ridiculous and
is an embarrassment to the serious reporting of climate change
The Mail on Sunday also suggests climate models overestimate how
much warming we will get in the future and by extension, the need
to bring emissions down.
In 2007, the IPCC
estimated a doubling of carbon dioxide above pre-industrial
levels was likely to raise global temperature by between two and
4.5 degrees Celsius, with a best estimate of three degrees. This
value is called climate sensitivity.
The Mail on Sunday says the new IPCC report "admits it is
'likely' [climate sensitivity] may be as little as 1.5 degrees
Celsius - so giving the world many more decades to work out how to
reduce carbon emissions before temperatures rise to dangerous
It remains to be seen exactly what the new report says about
The New York Times reported recently that the lower end of the
range of likely values has come down from two to 1.5 degrees since
the last report. We will have to wait for the report's publication
to see how the IPCC has tackled the issue.
But Myles Allen tells us Rose's suggestion that a revision of
the lower bound estimate on climate sensitivity could take the
pressure off efforts to reduce emissions is "patently absurd". He
"I have explained [this reasoning] to
David several times, and he does understand this, so he also
understands that any revision in the lower bound on climate
sensitivity does not affect the urgency of mitigation."
Richard Allan gives a good explaination of this point on his
University of Reading blog,
"[A]rguing over a few tenths of a
degree in climate sensitivity at the bottom of the range masks
the real issue which is the expected substantial climate change in
response to the continued emissions of greenhouse gases, which are
at present following the
worst case emissions scenarios."
The future of the IPCC
The piece also quotes Myles Allen, an IPCC lead author, in such
a way as to suggest Allen thinks the IPCC design and process is
flawed. Rose writes:
"One of the report's own authors,
Professor Myles Allen … last night said this should be the
last IPCC assessment - accusing its cumbersome production process
of 'misrepresenting how science works'.
For the record, Allen tells us he supports the continued work of
the IPCC to assess climate science:
"I did not say this should be the last
IPCC report, I said that in my view producing a massive volume once
every six years has become counterproductive … I would favour much
shorter annual update reports, plus special reports on specific
The IPCC won't comment on new material in the report before it
cautioning against drawing conclusions from the draft as the
findings are still subject to change. With the official version of
the summary for policymakers out next Friday, at least there's not
long left to wait now.