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Norway climate sensitivity research not yet peer-reviewed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 told.

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 air".

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 year.

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".

Climate sensitivity

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 cause.

In the Intergovernmental Panel on Climate Change (IPCC)'s last report, 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 models.

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 1.9 degrees.

Or at least, that's what the press release says, suggesting:

"It is the focus on this post-2000 trend that sets the Norwegian researchers' calculations on global warming apart."

In the press release, the findings carry the endorsement of Professor Caroline Leck of Stockholm University, who says:

"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."

Unpublished data

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 low end.

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 accepted."

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 press release.

This might raise the question of how the press release came to be produced.

Lower sensitivity?

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 the past.

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 1850, 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 Science, 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 700 metres.

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 climate sensitivity.

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 preliminary.

If nothing else, that might have helped avoid the confusion of the last few days.

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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.

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