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February 02, 2007

Follow Up: IPCC and Hurricanes

Posted to Author: Pielke Jr., R. | Climate Change | Disasters | Science + Politics

The IPCC report is out (PDF) and here is what it says about hurricanes (tropical cyclones). Kudos to the scientists involved. Despite the pressures, on tropical cyclones they figured out a way to maintain consistency with the actual balance of opinion(s) in the community of relevant experts.

Here is the discussion of observed changes:

There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures. There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long-term trends in tropical cyclone activity. There is no clear trend in the annual numbers of tropical cyclones.

Interestingly, in a table that discusses attribution of trends to anthropogenic causes it reports that there are some trends observed in some regions in tropical cyclone behavior, writing that these trends "more likely than not" represent the "likelihood of a human contribution to observed trend." But then this statement is footnoted with the following qualification:

Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena based on expert judgement rather than formal attribution studies.

So there might be a human contribution (and presumably this is just to the observed upwards trends observed in some basins, and not to downward trends observed in others, but this is unclear) but the human contribution itself has not been quantitatively assessed, yet the experts, using their judgment, expect it to be there. In plain English this is what is called a "hypothesis" and not a "conclusion." And it is a fair representation of the issue.

The projections for the future are as frequently represented in the literature:

Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs. There is less confidence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.

This comment on the process was offered by Australia's Neville Nicholls, who was one of the authors responsible for drafting the language on tropical cyclones:

"I was disappointed that after more than two years carefully analysing the literature on possible links between tropical cyclones and global warming that even before the report was approved it was being misreported and misrepresented. We concluded that the question of whether there was a greenhouse-cyclone link was pretty much a toss of a coin at the present state of the science, with just a slight leaning towards the likelihood of such a link. But the premature reports suggested that we were asserting the existence of much stronger evidence. I hope that when people read the real report they will see that it is a careful and balanced assessment of all the evidence."

The open atmosphere of negotiations in the IPCC is probably something that should be revised. How anyone can deny that political factors were everpresent in the negotiations isn't paying attention.

Posted on February 2, 2007 05:37 AM


Interesting. It confirms that yesterday's AP 'scoop' was not just misleading but, as some had expected all along, simply wrong ("The IPCC report is a marked departure from a November 2006 statement by the World Meteorological Organization...."). I doubt that AP will withdraw or correct the report. So much for the state of science journalism.

Posted by: Benny Peiser [TypeKey Profile Page] at February 2, 2007 07:05 AM

Benny- Call me a cynic, but my view is that the AP was either tricked into revealing an early draft by those wanting to create pressure on the process from the outside, or the AP was itself engaging in such behavior. The earlier drafts were an "open secret" and even can be found online.

The permeable IPCC negotiating process obviously needs some rethinking, as this case illustrates.

However, on the other hand score one for scientific leadership, as the IPCC narrowly avoided a major controversy. So perhaps the process worked after all.

Posted by: Roger Pielke, Jr. [TypeKey Profile Page] at February 2, 2007 07:34 AM


Thank you for your thoughtful and balanced assessment of what the IPCC SPM says. You have got it right. Your careful analysis on what the report says and how it compares to the WMO consensus statement is most appreciated.

Randy Dole

Posted by: Randy Dole at February 3, 2007 11:00 AM

Neville Nicholls comments about "misreporting and misrepresenting" lead me to wonder who Nicholls is thinking of? The better case would be that news media are doing the misreporting. Or perhaps journalists were mislead by advocates outside the IPCC process. The worse case would be that IPCC authors are misrepresenting; that IPCC authors were the source of the incorrect reports.

A similar question is posed by Rogers comment that the AP may have been tricked by those wanting to create pressure on the process from the outside.

Regarding the following report in the NYT one has to wonder if in this case the 'pressing" from the US and China was in the direction of keeping the IPCC in line with the existing consensus.

"Scientists involved in the discussions said Thursday that the U.S. delegation, led by political appointees, was pressing to play down language pointing to a link between intensification of hurricanes and warming caused by human activity."
The description of the source for the report indicates a scientist inside the IPCC process.

Posted by: Cortlandt [TypeKey Profile Page] at February 3, 2007 11:36 AM

Neeever mind. I was thinking by mass. My mistake.

I would like to know how, since climate is a balance of forcings, they can say that CO2 forcing has increased by 20% in the last 10 years. It seems that since temperature hasn't increased, CO2 forcing must not be that strong.

Posted by: Steve Hemphill [TypeKey Profile Page] at February 3, 2007 06:05 PM

It's absolutely wrong to say that global temperature hasn't increased in the last 10 years. Fitting a linear regression to the annual GISS global temperature from 1996-2006, the temperature rose by 0.29 C/decade. The linear correlation coefficient between temperature and year is 0.70-the p-value for the slope being greater than zero is 0.018. (Even if you start with the 1998 warm year, the regression indicates warming, although the significance isn't as strong, mostly because of the small number of points in the regression. If you use the monthly values from 1998-2006, the 0.19 C/decade estimate is highly significant, p=0.002.)

Posted by: Harold Brooks at February 3, 2007 06:29 PM

Steve Hemphill wrote: "temperature hasn't increased"

What in the world are you talking about? The steepest average rate of temperature increase in the whole global instrumental record is in the last 10-20 years (e.g., >0.3 deg C just since the first IPCC assessment in 1990, see the black line in AR4 Fig SPM-3(a)). That's part of the basis for the the IPCC AR4 conclusion that warming is "unequivocal."

Posted by: Scott Saleska at February 3, 2007 08:41 PM

Graceful summary, Roger, thanks.

But has anyone suggested that there aren't political factors present in the full IPCC negotiations?


Posted by: Scott Saleska at February 3, 2007 10:02 PM

You blew any credibility you had with me with that one, Steve.

Posted by: Mark Hadfield at February 4, 2007 11:58 AM

I notice nobody's taken on the 20% increase in CO2 forcing. What I'm saying is if the dogma is correct that ghg forcing is responsible for x (33?) degrees of warming on Earth and CO2 forcing has gone up by 20%, why is the warmest year still back in 1998?

Mark - good comeback ;-)

Posted by: Steve Hemphill [TypeKey Profile Page] at February 5, 2007 06:54 AM

As stated in the SPM, the 20% increase since 1995 is relative to the pre-industrial baseline greenhouse effect (~280 ppm CO2), not relative to zero ghg in the atmosphere. The natural greenhouse effect is irrelevant to the 20%. If 1995 was ~1 C higher than a natural greenhouse effect, we'd expect 20% higher radiative forcing to give an additional 0.2 C in 2005.

Interannual variability (the strong El Nino in 1998) is why 1998 is still the warmest year on record.

Posted by: Harold Brooks at February 5, 2007 07:47 AM

Steve, I withdraw my "lost any credibility" remark.

My underlying point was that to say temperature hasn't increased in the last 10 years is wrong, in my opinion. If you'd care to back it up, fine, but "1998 is still the warmest year on record" won't do it.

Posted by: Mark Hadfield at February 5, 2007 03:14 PM

Any word from Landsea? He walk out of IPCC based on the cyclones, and you're now saying that its OK. So I'm curious as to his reaction. has him saying "Landsea told Cybercast News Service his primary concern was with how lead authors representing the IPCC were interacting with the public and the media." - should we take that to mean that the report itself is OK by him?

Posted by: William Connolley at February 5, 2007 03:21 PM

My point is that the concept of ignoring natural forcing and saying that "forcing has increased by 20% in the last 10 years" is unbelievable sound bite bait, playing to alarmism. I can't believe that scientists, especially anyone that does modeling, would not cringe at that. If CO2 forcing truly increased by 20% in the last 10 years we would have undoubtedly seen a year warmer than 1998 - which we haven't. Since we haven't anyway, I don't see any justification for alarm bells - but it's not surprising, since we really have no clue about feedbacks. Forcings are easy, feedbacks are hard.

Also, I have a question on models. Do models calculate ppm changes by mass, or by mole?

Posted by: Steve Hemphill [TypeKey Profile Page] at February 6, 2007 06:20 PM

Steve asks:
Do models calculate ppm changes by mass, or by mole?

I don't know, but provided the models account for the concentration correctly, why would this specific choice of units matter? It's a bit like asking: Does the model use SI, British Units, or code everything in terms of non-dimensional parameters? Any method is fine as long as you do all conversions properly and don't screw up.

Posted by: margo at February 7, 2007 09:27 AM

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