Norway climate sensitivity research not yet peer-reviewed
- 28 Jan 2013, 17:36
- Roz Pidcock
A press release last week appeared to present the results of new
research suggesting earth's climate is not as sensitive to carbon
dioxide as scientists previously thought.
But Carbon Brief has been told that the findings came from
research by a PhD student in Oslo which has not yet been published
or accepted for publication by a scientific journal. The results
cited in the press release may change before publication, we were
The Research Council of Norway last week published a press
release entitled '
Global warming less extreme than feared?'.
It suggested it could be easier to contain global warming at the
accepted target of two degrees Celsius above pre-industrial levels
than "many experts have feared".
As you might expect with a story like this, the news release
sparked a deal of media interest.
The Express picked up the story, with the
headline "More signs that global warming is just hot
In the absence of a link to a published paper, Andrew Revkin
at New York Times blog
Dot Earth surmised the press release
referred to an
earlier paper by the Norwegian research
group, released at the end of last
But Professor Magne Aldrin, co-author on that
paper, told us today the press release refers to part of a PhD
thesis that remains "not published or accepted for
publication in a journal".
Temperature projections are based on scientists' best
estimates of climate sensitivity. This means how much warming a
doubling of carbon dioxide above pre-industrial levels will
In the Intergovernmental Panel on Climate Change (IPCC)'s
AR4, scientists estimated a likely range for
climate sensitivity of two to 4.5 degrees, with the most likely
value around 3 degrees. The range of uncertainty reflects the fact
that there are some key bits of the climate system - particularly
clouds - which aren't yet well represented by climate
What does the press release say?
The press release summarises research by Terje Bernsten,
professor at the University of Oslo and a
lead author on the IPCC's Fourth Assessment
Report in 2007.
It suggests rapid warming in 1990s led scientists to
overestimate climate sensitivity. Since about 2000, global mean
temperature has been rising more slowly.
According to the Norwegian research, using data up to the
year 2000 in the scientists' model produced an estimate of climate
sensitivity of 3.9 degrees Celsius. But when temperature data after
2000 were included, the estimate came right down to
Or at least, that's what the press release says,
"It is the focus on this post-2000 trend
that sets the Norwegian researchers' calculations on global warming
In the press release, the findings carry the
endorsement of Professor Caroline Leck of Stockholm University, who
"These results are truly sensational. If
confirmed by other studies, this could have far-reaching impacts on
efforts to achieve the political targets for climate."
In suggesting a climate sensitivity estimate of 1.9 degrees
Celsius, the Norwegian research would not necessarily be
inconsistent with the IPCC's estimates - but it's definitely at the
But it may be a bit premature to ask how they can be
reconciled. We have been told that the findings presented in the
press release have not yet been accepted for publication by a
scientific journal - and so are not yet peer reviewed.
Dr Magne Aldrin, co-author on the 2012 paper with Terje
Berntsen, told Carbon Brief today:
"The results mentioned in the press
release by the Research Council of Norway is taken from [a] PhD
thesis ... from March 2012 and that part of [the] PhD thesis is not
published or accepted for publication in a journal."
Aldrin told us last December that the group's newest
findings - an extension of the analysis in the PhD thesis - were
under review with the Journal of Climate. He told us today that is
still the case, adding that the PhD thesis findings should be
thought of as "preliminary" and that the "final result is not ready
yet". He continued:
"[W]e currently work on a revised
version [of our climate sensitivity estimate], and the final
results may differ from those given in the PhD thesis ... since we
have extended our analysis further. The new paper has not yet been
So it appears from this the press release is based on work
that has not yet been peer-reviewed, and the findings which the
group do intend to publish may differ from those reported in the
This might raise the question of how the press release came
to be produced.
This isn't the first time the argument has been made that
the IPCC has overestimated climate sensitivity - and such arguments
usually involve looking back at how the climate has responded in
Professor Richard Lindzen has suggested that climate
sensitivity could be as low as 0.7 degrees - but his views have
prompted wide disagreement
from other scientists. Using temperature observations since
a paper from last year by Magne Aldrin
co-authored by Bernsten estimates an average climate sensitivity of
about two degrees. Another
study which looked at temperature data since the
last glacial maximum estimated a median value of 2.3 degrees -
which is at the lower limit of the IPCC range.
But the most likely value is around 3 degrees according to
the IPCC, and it appears from leaked drafts of the newest IPCC
report that their assessment of the science hasn't changed
significantly since 2007.
In a piece for climate science blog Skeptical
Dana Nuccitelli suggests that the model in the new
Norwegian study could be too reliant on short term variability. He
also says the researchers could be underestimating climate
sensitivity by failing to include the role of the deep ocean, below
Where does all this leave us?
There is a debate going on in the scientific community about
climate sensitivity. Although there is a most likely value
according to the IPCC, higher (and lower) values for climate
sensitivity cannot be ruled out.
New scientific research will no doubt continue to refine and
challenge the IPCC's estimate - and it may be that when these new
results are eventually published they do suggest a lower figure for
But this episode underlines the problems of so-called
science by press release. With such a complex and sometimes
controversial topic, research findings need to be carefully
treated. As with all scientific research, if results are not yet
published or peer reviewed, they are worth treating as
If nothing else, that might have helped avoid the confusion
of the last few days.
Update - There's
a good post on Andy Revkin's Dot Earth blog which kindly
cites this blog. Revkin has got more reaction from scientists, and
a lot more detail on the study. Worth a read. We had also said a
study estimated a mean value of climate sensitivity of 2.3 degrees
- we should have said median.