Out on a Limb II: A Verrrry Looong Limb
April 12th, 2006Posted by: Roger Pielke, Jr.
Kerry Emanuel and Michael Mann have a draft paper (which I haven’t seen, but I’ve seen Kerry present) in which they argue that the multi-decadal patterns of active/inactive hurricane periods in the Atlantic are mainly a function of anthropogenic forcings, including greenhouse gases and aerosols. Related to this work Emanuel makes a bold forecast reported in today’ Palm Beach Post:
“It’s unlikely we’ll ever see a quiet decade [for hurricanes] for the next 100 years in the Atlantic.”
I wonder if we’ll soon hear industry in the eastern US asking for relief from the Clean Air Act requirements justified in terms of reducing hurricane impacts (joke). More seriously, it’ll be a long time before Kerry’s prediction can be evaluated against observations, however, in the short-term, it simply adds to the overwhelming case already in place to enhance resilience to hurricane impacts in those regions known to be at risk to hurricane strikes.
April 12th, 2006 at 9:47 pm
As Keynes said, in the long run we are all dead. Considering that even Gray and co say we are in for a bad decade or two this is a pretty safe bet in the next twenty years or so, by which time it will not matter (for good or ill).
April 13th, 2006 at 8:37 am
This is the abstract from a paper co-authored by Mike Mann, published just last year:
Knight, J.R., Allan, R.J., Folland, C.K., Vellinga, M., Mann, M., 2005. A signature of natural thermohlaine circulation cycles in observed climate. Geophysical Research Letters, doi:10.1029/2005GL024233.
“Analyses of global climate from measurements dating back to the nineteenth century show an ‘Atlantic Multidecadal Oscillation’ (AMO) as a leading large-scale pattern of multidecadal variability in surface temperature. Yet it is not possible to determine whether these fluctuations are genuinely oscillatory from the relatively short observational record alone. Using a 1400 year climate model calculation, we are able to simulate the observed pattern and amplitude of the AMO. The results imply the AMO is a genuine quasi-periodic cycle of internal climate variability persisting for many centuries, and is related to variability in the oceanic thermohaline circulation (THC). This relationship suggests we can attempt to reconstruct past THC changes, and we infer an increase in THC strength over the last 25 years. Potential predictability associated with the mode implies natural THC and AMO decreases over the next few decades independent of anthropogenic climate change.”
Whenever I bring this up over at RealClimate, in support of the notion that the AMO is a natural phenomenon, Mike accuses me of misreading the paper. So, I’ll let you all decide because apparently my English skills are slipping.
April 13th, 2006 at 11:00 am
As Chip knows very well, the issue is not whether the AMO exists or is natural, but whether it contributes significantly to the variations in tropical Atlantic SSTs. In the model simulations discussed by Delworth and Mann and Knight et al it is a very small component, and the analyses of Emanuel suggest that the observational data doesn’t support that either. Mann and Park (1999) also support the idea that there is an AMO, but that it doesn’t impact tropical SST substantially. Some of the more naive ways to extract an AMO signal (linear detrending) give rise to obvious problems when the forced component is non-linear, as should be clear to all.
April 13th, 2006 at 12:36 pm
Roger,
What would your quess be about what the folks over at Swiss Re are thinking?
Bob
April 13th, 2006 at 2:03 pm
Bob- Not sure, but here is a hint, I’d guess:
http://www.insurancejournal.com/news/national/2006/03/23/66705.htm
April 13th, 2006 at 2:41 pm
As Gavin well knows (to borrow a favorite rhetorical device from RC) hurricane researchers were quick to point out a change in the climate of the tropical Atlantic that was associated with the active hurricane season of 1995 and postulated then that we could be returning to a more active hurricane regime that would likely last for several decades. The persistence of active years following 1995 further strengthened this belief that a regime change had occurred. If there are not active and inactive cycles in Atlantic hurricane activity, then this was merely a wild coincidence that hurricane researchers got it right in the mid-to-late 1990s.
Or maybe it wasn’t a coincidence at all. Perhaps anthropogenic changes to the tropical atmosphere just gave rise to an apparent cycle over the past 75 years, part of which was an abrupt change in the mid-1990s to conditions that promoted more frequent and intense hurricanes in the Atlantic. The problem with this theory (among others) is that the character of the post-1994 changes in the tropical environment in the Atlantic doesn’t nicely match climate model projections of how they should have evolved and what effect they should have had on tropical cylones. This presents a bit of a quandary. If it is anthropogenic global warming, then the models are wrong about its character and its effects, if it is not anthropogenic global warming, then a valuable sales device is taken off the table.
No fear though, there is a way out: 1) observations of the tropical atmosphere are in error (general circulation models get it right after all) and 2) the response of tropical cyclones to these (human-induced) changes is non-linear and isn’t properly handled by the hurricane models (i.e. it is even worse that we expected).
In keeping with the Prometheus’ post theme, I will go out on a limb here and predict that we will soon come to be told by those climatologists who have assumed the role of distributors-of-the-truth, that there is no aspect of the observed climate over the course of the past century or so that is primarily of natural origin—humans will be shown to have a hand in everything—and that anyone claiming that natural cycles are responsible for any significant part of any observed climate change will eventually be shouted down and dismissed. Of course, this is hardly much of a prediction, as it is largely already the case. I just feel so bad for all those scientists who worked in climatology prior to the mid-1980s for all their work was largely for naught as they didn’t understand the fundamental cause giving rise to their observations and thus had to come up with silly theories to explain them. Everything falls into place when the sun is the center of the solar system or when mankind is the root of all evil. I have yet to embrace the latter.
April 13th, 2006 at 7:54 pm
No, no, Chip, it’s the *coal industry* that’s the root of all evil. But you knew that.
Less snarkily, what else were hurricane researchers supposed to conclude when they saw the increased SSTs associated with the hurricane activity increase in the mid-90s? It wasn’t a very amazing leap to suggest that whatever was adding the heat was likely to persist absent any other knowledge. Chalking it up to the AMO (or some other climate cycle) sounds better than admitting ignorance, but to say that it’s the AMO without being able to say exactly how the AMO added the heat is really just admitting ignorance in a different way.
April 14th, 2006 at 8:35 am
Steve,
There is far too much focus on SST in the current debate on hurricane intensity. SSTs are only one of a bunch of factors that effect the ultimate intensity that a hurricane reaches.
This is what Chris Landsea et al. had to say back in 1998 (Monthly Weather Review, 126, 1174-1193) in reference to the very active 1995 season:
“(Some have asked (e.g. Begley 1996) whether the increase in hurricanes during 1995 is related to the global surface temperature increases that have been observed over the last century, some contribution of which is often ascribed to increases in anthropogenic “greenhouse” gases (Houghton et al. 1996). We conclude that such an interpretation is not warranted, particularly in light of the large scale patterns of oceanic and atmospheric conditions that can be linked coherently and tangibly to the observed interannual variability of hurricane activity.”
The point being that hurricane researchers have long known about multidecadal variations in the number of intense hurricanes and in environmental fluctuations that have been associated with them. And SST has not been the primary player–but at the same time, it is not an inconsequential one either.
Since 1995 a combination of environmental factors in the tropical North Atlantic have been in place that are favorable for intense hurricanes:
1) SSTs are high
2) atmospheric stability as declined
3) vertical wind shear has declined
And many of these conditions became favorable rather suddenly starting in 1995.
Number 1 is projected by GCMs. The opposite of Number 2 is projected by GCMs (they project increasing stability). And GCMs are relatively silent on Number 3 (that is, they show no real strong projections either way).
So, most likely what we are experienceing is some combination of greenhouse-induced SST increases contributing to some unknown degree to other changes in the tropical environment that are probably of natural (quasi-cyclical) origin.
Neither mankind, nor Mother Nature, should be given all the credit or all the blame.
April 16th, 2006 at 8:02 pm
Chip, there’s little point in arguing with you on the substance of this, but I just have to ask: Quasi-cyclical? What random natural variability (i.e., noise) wouldn’t be prone to describing with this term?
April 17th, 2006 at 7:11 am
I heard Kerry speak last Friday at the National Hurricane Conference in Orlando and quickly realized that her analysis of tropical activity is simply and seriously flawed. Her argument rests entirely on the assumption that the available records on historical tropical activity are accurate. When questioned on this specific point, she admitted that the older records are wanting but “…they are the best that we have”, implying that we should accept the records as they are.
On the face of it, her answer was not incorrect, but it was misleading. We know how the records are inaccurate. They underestimate the actual number and intensity of tropical storms in the past!
Dr. Neil Frank, Director of the National Hurricane Center in the 1973-1987, commented that if the 2005 season had occurred pre-WWII, we would have had at least 5, and as many as 8 fewer named storms, simply because we would not have detected them. He also pointed out how the ever-increasing ability to measure these storms results in an increase the number of higher category storms.
Max Mayfield, current director of the Hurricane Center, announced that one of last years tropical storms was being upgraded to a hurricane based on a reanalysis of new Doppler radar data from a NOAA plane. The Doppler detected hurricane force winds that were missed by the satellite, dropsondes, bouys and ground observations. Later this year, the new Doppler radars will be installed in all the Air Force Reserve planes that do the vast majority of the recon flights. This will obviously result in an even greater ability to detect the strongest winds, which will lead to higher categories than previously. Throughout the 20th century, advances in technology and observational coverage have had similar effects.
Even the methodology for upgrading a storm has changed at the Hurricane Center over the last three decades. Dr. Frank confided that in the 70’s and 80’s, they wanted to see more persistance in a storm before upgrading it. If the pressure did not support the observed winds, they would hold off until the next observation period to see if the winds were still there before making the upgrade. They don’t hold off any more.
All of these factors and more creat a general upward trend in the number and strength of tropical cyclones in the Atlantic and Eastern Pacific over the historical record. Similar problems exist in the other tropical basins and have been well documented.
While we can not improve the observations from the past, we can ‘level’ the data by analysing the more modern records with the older methods. When this is done, the upward trends virtually disappear, removing evidence of an anthroprogenic effect. What is left is the cyclical pattern in the Atlantic Basin.
The Kerry/Mann argument is based on a false premise and should be disgarded outright. It will be interesting to see how this paper is received by the press and the scientific community.
April 17th, 2006 at 7:49 am
Unless something drastic has happened since I last saw him in October, Kerry Emanuel is male. Perhaps you saw Judy Curry last week. I doubt if what Judy had to say was more than tangentially relevant to the Emanuel/Mann work.
April 17th, 2006 at 10:24 am
Harold,
You are absolutely right on the first part. I saw Prof. Judy Curry at the Hurricane Conference, not Kerry Emanuel. Her presentation was still very much on my mind early this morning when I read Roger’s topic and associated Curry with Kerry. I apologize to both of them and to all readers. I actually returned to the site to make the correction, but you had already caught me.
As for the two works being unrelated…I have my doubts. Both try to tie the hurricane record to anthroprogenic forcing. The only way to show a coorelation between increasing anthroprogenic forcings and tropical cyclones is to show some kind of a trend in tropical cyclones. I know Curry ignored obvious shortcomings of the data base to reach her conclusions. I think Emmanual and Mann will have to do the same thing. We shall see.