Hurricanes: A new and improved hockey stick

Another silly debate around the IPCC report

Posted by Andrew Dessler (Guest Contributor) at 1:55 PM on 01 Feb 2007

Read more about: climate | climate science | IPCC | climate change skepticism

News stories have been reporting that the IPCC will make a statement about the relation between global warming and hurricanes:

During marathon meetings in Paris, the Intergovernmental Panel on Climate Change approved language that said an increase in hurricane and tropical cyclone strength since 1970 "more likely than not" can be attributed to man-made global warming, according to Leonard Fields of Barbados and Cedric Nelom of Surinam.

The blogosphere is already awash with discussion about this (see here and here), and I expect all the usual suspects to weigh in on this soon.

Some commenters have been arguing that this statement fundamentally disagrees with a recent statement by the World Meteorological Organization (WMO). The implication is that this disagreement shows that the IPCC process cannot be trusted -- and therefore, we should not believe the IPCC's conclusions.

Let's compare their statements. In the IPCC's language, "more likely than not" means something like a 51% chance -- a smidge more than a coin flip. The alternative phrasing by the WMO is that while there is evidence "both for and against" a connection, "no firm conclusion can be made at this point." (PDF here).

To my eye, these statements mean pretty much the same thing. But like the hockey stick debate, I suspect that doesn't really matter much. What matters is that this mole hill will be blown up to a mountain by advocates who want to use this difference to launch attacks on the IPCC.

Sadly, this delightfully noisy but substance-free argument will take away from the IPCC's most important result: the Earth just keeps getting warmer, and we're primarily to blame.

(Also see my previous post on why we should trust the IPCC here.)

For story: Hurricanes: A new and improved hockey stick
10 Comments | Post a Comment

Excellent post

Dessler: "What matters is that this mole hill will be blown up to a mountain by advocates who want to use this difference to launch attacks on the IPCC."

Yep. And it looks like one of the usual suspects is launching a preemptive strike.

Benny Big Eye

by Benny Big Eye at 1:59 PM on 01 Feb 2007

51%

Andrew, AFAIK the IPCC doesn't have a category that can be used to reflect something like a 51% likelihood. Unless a new category has been invented, all they have is "as likely as not" for 33% to 66%, moving up to "likely" for 66% to 90%. There is no "more likely than not" as quoted in the AP story.

by Steve Bloom at 6:32 PM on 01 Feb 2007

That's right

Steve-

You're correct. Footnote 7 of the TAR WGI SPM did not list anything like that. On the other hand, "more likely than not" has a reasonably simple interpretation --- more so than words such as "likely". I'll be quite interested to see what actually comes out in the report.

by Andrew Dessler at 7:17 PM on 01 Feb 2007
[ Parent ]

New categories it is

Sure enough, they added a couple categories and changed the ranges, as would make sense in order to reflect finer-grained results.

Virtually certain > 99% probability of occurrence,
Extremely likely > 95%,
Very likely > 90%,
Likely > 66%,
More likely than not > 50%,
Unlikely < 33%,
Very unlikely < 10%,
Extremely unlikely < 5%

Hmm, "less likely" seems to be missing in action. Maybe they don't use it anywhere.

by Steve Bloom at 2:52 AM on 02 Feb 2007

Hurricanes and the Commissioner's view of AGW

I attended the biennial Galveston Bay conference last week and saw a great presentation by one of your collegues, Jennifer Irish. Basically it floored everyone. The gist was that hurricane intensity (max. sustained winds) maybe a poor way of gaging storm strength and subsequent damage. Rather, storm size (distance from eye to area of max. winds) and wind speed are a better indicator of storm surge (the most damaging aspect of the storm) height. Katrina and Rita, a category 3 and barely a 2, were very large, intense storms, fueled by passage over warm loop currents in the Gulf, which radically dropped in wind speed during eye wall replacement cycles and increasing shear. Turns out the drops in wind speed did little to reduce their storm surge and destruction. I think when the NOAA and AMS folks state that AGW's effect on storm intensity is unknown, they are doing so knowing that max. wind speed is a tricky thing to predict and isn't essentially tied to sea surface temps. However, it turns out that AGW caused increases in storm size and subsequent damage maybe more easy to predict using sea surface temp changes. More work needs to be done investigating how AGW will effect Gulf loop currents, etc. Any thoughts?

Lastly, Larry Soward, the commissioner of the Texas Council on Environmental Quality (our air and water quality agency) and the govenor's former chief of staff, gave the closing address. Started out normal, great job everyone etc., and then suddenly it seemed like he dropped his notes and went on a tear about how there is no downside to the reduction of green house gases. He discussed the adverse effects of climate change and rising seas on Texas very eloquently. The conference gave him a spontaneous standing ovation. Afterwards I learned it was the first time he gave this address. This is the agency that will have to approve new coal fired power plants in Texas.

Andrew Sipocz

by asipocz at 9:19 AM on 02 Feb 2007

Andrew Sipocz,

That's quite interesting about Soward. Do you know if his address was recorded?

grist.org

by David Roberts at 9:22 AM on 02 Feb 2007

Soward Address

I don't believe so, neither were the press present. It was an astounding pronouncement. We'll have to see what happens when the agency he heads reviews the dozen or so coal-fired power plants that TXU wants to build.

Andrew Sipocz

by asipocz at 10:53 AM on 02 Feb 2007
[ Parent ]

Thanks Andrew!

We need good news! Very encouraging. We should all remember Texas also has a lot of progressive reform minded citizens. I forget that too from time to time.

Texas is number one in wind power, I think? In growth and installed capacity.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

by amazingdrx at 12:35 PM on 02 Feb 2007

Question about semantics and interpretation

Hi Andrew,

Could i ask you to put me on the right track here, since i'm discussing global warming and hurricanes in another forum.

The trouble i'm having is to define which statements that are acceptable in light of the WMO and/or the IPCC consensus. I'll use Katrina here as an example - but this really isn't about it. The discussion boils down to these two statements:

Katrina was caused by global warming
Katrina was not caused by global warming

From my personal reading both of these two statements are wrong. I know that its not possible to pin down the attribution in intensity to a single event, and i'm also well aware that the AMO probably has a much larger impact on north atlantic cyclones, and that land-use changes and development is the real culprit in the damages from hurricanes (both for Katrina and in general), since i do read prometheus once in a while...

Hopefully you can help me in assessing whether i'm correct or entirely off track in this. I don't mind being wrong - i'd rather correct any mistakes that i've made.

Thank you,

Kim.

by merwin at 6:11 AM on 08 Feb 2007

You're right

Kim-

It is impossible to attribute (at least with our current knowledge) any single event to global warming. Ditto for saying that global warming had no effect on any single event.

So, as you surmised, both statements are wrong: we cannot say what effect global warming had on Katrina.

What can you say? From the IPCC: 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.

by Andrew Dessler at 7:58 AM on 08 Feb 2007
[ Parent ]

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