The idea that human induced climate change has increased the number and/or the intensity of hurrincanes is a hypothesis at this point. It might indeed turn out to be true, but it can’t be called a theory yet, in the scientific sense of that term.
There are longer-scale climatic changes that make it very difficult, if not impossible to determine whether global warming is affecting hurricane amounts/intensity in the North Atlantic. A big potential player is the North Atlantic Oscillation. Now I am not a climatologist, but as a meteorologist it is all very interesting.
There seems to be a very complex relationship between ocean temperatures, salinity, and stratospheric wind patterns. In fact, so complex that I seem to recall that the NAO was not “discovered” until relatively recently (1990s maybe? I’m guessing here). A positive NAO index (defined as the averaged pressure difference between the subtropical high and Icelandic low) results in stronger winter storms in the Atlantic, and typically warm winters in Europe and the eastern US, with colder than normal temps in eastern Canada. A negative index will roughly have the opposite affect. A negative index is correlated with more frequent hurricanes in the Atlantic. Standarized seasonal means indicate positive anomalies for much of the 1980s, with the index becoming generally negative around 1995, which was the year hurricane activity in the Atlantic ramped up.
An interesting thing I found out, some theories are that with global warming (increased CO2) and ozone depletion, would result in a stronger than normal polar vortex (Icelandic low), which would result in a generally positive index. So, if these theories are correct, and all other things are equal (El Nino-Southern Oscillation among other things), global warming would actually limit the amount of hurricanes in the Atlantic.
As for intensity, it is very difficult to determine if increased water temperatures lead to increased intense hurricanes. Some of the many variables to consider:
- Satellites for weather observation weren’t launched until 1960.
- Satellite-based intensity estimates were only first developed in the mid-1970s by Vern Dvorak, and are still being updated today.
- Based on recent data from within the past 10 years, some of the algorithms used to estimate surface winds based on reconnaisance aircraft measured winds, have been updated (one reason Hurricane Andrew in 1992 was upgraded to a Cat 5 in 2002, 10 years later).
- Based on #3, the Hurricane Research Division (part of NOAA) is re-analyzing all storms back to the 1850s (and have even found some new ones), using the latest scientific research. This research is only complete until 1914 or so.
What I’m trying to get at, is that observing techniques have changed markedly since the 1800s (where the only hurricanes we knew of were ones that hit land, or were by chance sampled by ships at sea…so there are some that we will never know about), and intensity estimates have changed through time as well. So, as of now, merely based on sampling methods, it’s tough to say whether intensity has gradually increased through the years. Since observations have been all over the place, it’s impossible to determine how global warming or the NAO (or even ENSO) affect intensity. The Re-analysis Project when complete, will hopefully give us a better understanding of this.
In summary, number of hurricanes may become less common due to global warming, however intensity-wise, there is absolutely no way to tell beyond guesses at this point.
That was a very informative post, Viscera. Thank you.
What a ridiculous statement for you to make. First off, what gave you the impression that I question Evolutionary Theory? Secondly, I was under the impression that Evolution is both theory and fact. Thirdly, Evolutionary theory has stood the test of time despite many tests to it (you know…TESTING the theory to ensure its correct? Sciences and all that)…and continues to be tested to this day. It is actually possible that another theory will come along to superceed the theory as our understanding of Evolution continues to grow…just like the theory (or perhaps hypothesis is a better word as John Mace and SuaSponte pointed out) of Global Warming needs to be tested before its accepted as fact. The Global Warming hypothesis/theory is still in its infancy and to correlation of Global Warming to more frequent or more severe hurricanes is still not well understood…and there seems to be no consensus from the folks who actually know what the hell they are talking about, as opposed to you and I.
Look up the word ‘irony’ sometime…
Viscera, well said.
-XT
You can say more than that. You can say that climate simulations predict that increased CO2 will increase hurricane intensity, and that the data we have since 1970 -the satellite era- are consistent with those models. That is a lot more than a guess.
I was in reference to Viscera BTW.
Viscera: According to Kerry Emanuel’s FAQ on the subject that I linked to before, the situation for measuring intensity changes over time is not as bad as you seem to imply.
Do you have evidence to support this as the accepted view? I’d rather heard it the other way around: I.e., there is very little beyond guesses to be made in terms of hurricane frequency but that in terms of intensity, there is pretty good understanding that global warming is likely to lead to higher intensities and now some evidence that this trend is being detected. See, for example, the Kerry Emanuel FAQ, the RealClimate piece that I linked to above, and is a recent Perspectives piece in Science by Kevin Trenberth. Also, [url=http://www.grida.no/climate/ipcc_tar/wg1/388.htm#box102]here is what the IPCC had to say on the subject in 2001, which may be getting a bit out of date.
The existence of the hypothetical decadal cycle is by no means firmly established. For one thing, the data only goes back to 1900…which provides good sample size for individual years, but is far too short a time span to say anything about repeating 30-40 year cycles…especially since there’s a massive unknown in the latest equation.
I don’t. I was just pointing out that dismissing global warming affecting hurricanes as a theory made as little sense as dismissing evolution as a theory. No one is making claims for either as facts, just working theories.
Actually, my sense is that there is a huge scientific consensus in favor of the notion that global warming is occurring, will almost certainly have bad consequences, and we should try to ameliorate its effects sooner rather than later. The majority of the opposition seems to come from persons allied with industries who don’t want to see themselves forbidden to dump stuff freely in the atmosphere.
To DSeid: I would like to say that I am not very familar with the various climate modelling schemes, but increased CO2 and stronger hurricanes seems to make sense.
To jshore: [ur;=http://www.ldeo.columbia.edu/~visbeck/nao/presentation/html/img17.htm]Here is the link where I got that information. I must stress this is not the accepted view. Theory in this case is the generic theory, and not the scientific “theory”.
Finally, and I must apologize for not being clearer, my post was only based on the North Atlantic and the NAO (since these would affect storms that affect the US), and how global warming related to it. Global warming would affect all basins, so I’m confident that I’m not inconsistent with the earlier links, which seem to be talking about worldwide storms. Who knows how the other known and unknown patterns on short- and long-term scales (such as ENSO, and the Madden-Julian Oscillation, a 40-50 day cycle of increased convection/tropical storms in the Indian and Pacific oceans), that we don’t know the causes of. IMO, until we know the methodologies of these cycles, it may very well be tough to model it.
Here is the link.
jshore,
As I understand it, the IPCC global warming theory has it that due to the man-made increase in CO2 the atmosphere will heat up first. This additional heat captured by the CO2 in the atmosphere will in turn heat the oceans.
As far as I know, the IPCC observations and calculations show the current atmoshperic temperature change over the last century has been around +.5 degrees. While the Atlantic Basin area of the ocean temperature has increased around +1 degree.
The theory says atmosphere heats up first, then it heats the oceans. The observations say both are heating up, but the ocean is heating up faster.
This seems to be a contradiction in the IPCC global warming theory or at the very least an indicator that something besides just man-made CO2 is increasing the temperature of the ocean and possibly even the atmosphere.
If this actually is a contradiction, wouldn’t it just be global warming scare mongering to come out and say the IPCC global warming theory supports the claim the current trend increase in category 4 and 5 hurricanes is due to man?
That, and most of the hurricane experts I have read about have only distanced themselves from trying make that assertion, makes me even more dubious about these types of causal links that are trying to made by the global warming consensus crowd about the bad weather the earth is currently experiencing.
It would seem beneficial for the IPCC consensus crowd to actually PROVE their global warming theory BEFORE they then try and make causal relationships with it, IMO.
Water has a much higher specific heat, and loses thermal energy less quickly. If global water temps. are lower, on average, than atomospheric temps, then the effects on water may accumulate more rapidly on average than the atomosphere over annual cycles, even if atomospheric warming is what’s driving the change.
The higher specific heat of water also means that it takes more energy to raise the water temp which usually means it takes more time. I have never even seen an IPCC report that claims the current IPCC attributal increase temperature in the atmosphere due to man has increased the oceans temp. The IPCC reports do say it WILL increase the ocean temp but not that it HAS increased it.
In any case, your comments do not prove the atmosphere is the driver in the rising ocean temps.
I am all for hypothesising about what is causing what. But, to try and concretely connect the IPCC global warming theory with observed temp changes in the atmosphere and then to the oceans AND then to the increase in category 4 and 5 storms over that past few years is too much of a stretch for the science to support. yet. I am certainly not saying it is not happening. I am saying we don’t know it is happening. yet. Until we know we can’t say it is. We can say it might be though.
Nor do your comments disprove it. The point in the hypothesizing is I could talk out of my ass as easily as anyone who might say “the water is getting warmer faster than the air, and hence this premise is false”. Call me weird, but I’m guessing this little paradox might have occurred to the thousands of climatologists who pour over these statistics with a fine tooth comb every day, and there’s a more elegant resolution to the paradox than your simplistic “if A then not B” analysis.
I do agree that climatologists are pouring over the statistics to try and figure all this stuff out.
That doesn’t prove it is man-made global warming causing it either.
There may be a solution to my supposed paradox. You haven’t given it though.
Thanks for trying.
Grey Matters:
(1) It is not the “IPCC global warming theory”. The IPCC is a scientific body set up by the U.N. to review the peer-reviewed science periodically and give reports about the current state of the science in the peer-reviewed scientific community.
(2) Do you have a citation to this issue of ocean temps vs. air temps? I hadn’t heard about any such discrepancy. My intuition is that the top layer of the ocean will tend to track more or less with the air temperature. Perhaps you are confusing the fact that the oceans are a large source of thermal inertia? I.e., in the absence of the oceans, the atmosphere would equilibrate with the current level of greenhouse gases much more rapidly than it does. However, because it takes so much energy to heat the oceans, the equilibration is much slower…and the heat does take a while to penetrate down very deeply into the oceans. However, I wouldn’t imagine there would be a large discrepancy between the heating of the atmosphere and the upper layer of the ocean. Also, there was a recent study of the structure of the ocean warming that showed that it is very compatible with what is expected on the basis of the increase in greenhouse gases and not at all compatible with any alternative hypothesis of increase in solar radiation. (Penetration of Human-Induced Warming into the World’s Oceans; see also this accompanying Perspective. The article Earth’s Energy Imbalance: Confirmation and Implications by J. Hansen et al. is also relevant where they looked at increases in ocean heat content over the last 10 years to determine the amount by which the earth is currently radiatively out of balance and used this to calculate the amount of additional warming that we are already committed to by the current levels of greenhouse gases in the atmosphere. This piece on RealClimate gives a popular account of the Hansen et al. work.)
(3) The warm sea surface temperatures (SSTs) in the tropical Atlantic right now are believed to be in part cyclical and in part due to global warming, with the rough breakdown being 50-50. See this RealClimate piece that I linked to.
(4) You cannot “prove” anything in science. Science is inductive, not deductive. like mathematics. (You can prove things in mathematical physics, for example, about certain mathematical models of natural processes but these just prove things about the models’ behavior, not necessarily nature’s behavior.) The theory of gravity and the theory of evolution are not proven. To ask that global warming be “proven” is non-sensical. What happens in science is that the evidence accumulates until fewer and fewer scientists hold out against the theory. However, the last few hold-outs can last a long time particularly when there is lots of money and strong political / philosophical convictions at stake.
(5) What I have linked to are discussions of the science by the IPCC review, a peer-reviewed article, a discussion by the person who may be the foremost expert on the subject (Kerry Emanuel) based on a recent article he published in Nature, and some further discussion of his and other works by scientists in the field. I think they know better than either of us the extent to which one can make the connection between hurricane intensity and anthropogenic global warming. As I have noted, it is not certainly not clear-cut yet on this issue, but some things are beginning to emerge. Why don’t you read what they have to say?
It’s reading comprehension skills like this that make me wish I hadn’t bothered.
Let’s be clear on what all we’re saying.
First, playing off the " evolution is both theory and fact" thing, so is global warming (allowing for the idea that it’s not a ‘proven theory’ if you’ll accept that phrasing for something demonstrably accurate).
World temperature averages have incremented by a small amount. Several effects (e.g., melting in the Beaufort Sea off northern Alaska) that can only be reasonably attributed to a global warming trend have occurred.
So much for “fact.”
Now, the general consensus among those concerned about it is that (a) it’s a new trend, (b) it’s caused at least in large part by human activity, and © it may well have dire consequences.
There is some evidence to indicate that the global temperature cycles in three distinct cyclic processes, with the actual mean planetary temperature the result of all three (plus any extraneous influences).
There is some evidence suggesting that anthropogenic greenhouse-gas emissions are contributing to the effect.
The dire consequences are inferential, not strictly demonstrated.
Do I think it’s happening? Yes. Do I think human influence is partly to blame? Yes
But it’s such a massive multivariable problem that the degree to which it’s part of natural cycles, to which it’s caused by human effects, and to which it’s likely to have deleterious effects on future existence, are all so up in the air at the moment.
I think it’s reprehensible to ignore the data, and attempt to besmirch its validity, because of its potential negative effect on the big business political base, as some conservative Republicans (not, I think, Bricker) are inclined to do. I think it’s equally reprehensible to assume that “it’s all our fault, and we need to stop burning anything today” as some of the Chicken Little school of environmentalist seem to do.
But the truth of the matter is, we need more facts, more evidence over a longer span, to formulate anything like an accurate theory. And it wouldn’t hurt to figure out low-impact-on-society ways to reduce the amount of greenhouse gases we emit while we’re getting them, as that definitely is making at least a minor impact on what’s happening. We need not be Ostrich or Chicken Little, but instead we should be finding out the truth and then acting on it.
Polycarp: Your summary may have been accurate about 10 or so years ago. But I don’t think it is today. The 2001 IPCC report concluded that most of the warming in the last 50 years was likely due to the human-caused increase in greenhouse gases…and there has been a considerable strengthening of much of the evidence over the last few years (such as the recent study I linked to above of the structure of the warming of the oceans). There is a whole field of “detection and attribution” that has been working on this issue of detecting the warming and determining the cause.
Also, it is not a matter of just observing a warming and theorizing what it might be due to. The rise in CO2 and other greenhouse gas levels in the atmosphere and its attribution to human activities is beyond any serous doubt. The amount of radiative forcing caused by a given increase in CO2 in the atmosphere is well-understood…namely that a doubling of the CO2 will cause about 3.7 W/m2 of forcing (at the top of the atmosphere, if I remember correctly). It is also not hard to calculate what that forcing corresponds to in terms of the warming if the earth behaved as a simple “gray body” radiator having its known “albedo” (reflectance).
The only question that remains from a theoretical point of view is figuring out all the feedbacks that occur in the real climate system. Admittedly, this is far from a simple task…But, more and more is being understood. The general belief has been that these feedbacks (particularly the “water vapor” feedback) would cause a magnification of the “gray body” prediction by about a factor of 2 or so. So, the only way to get around this is to propose either some strong negative feedbacks and/or reasons why these positive feedbacks don’t occur. Richard Lindzen tried valiantly with his “iris effect” to come up with a strong negative feedback due to clouds but the data doesn’t seem to support his hypothesis and, furthermore, it becomes really hard to explain the general instability of the climate system to roughly estimatable forcings that caused the ice age - interglacial cycles if there is really this strong a stabilizing factor around. And, more evidence is accumulating in support of the water vapor feedback. Just in the last few weeks, a paper in ScienceExpress showed that satellite measurements are in agreement with the moistening of the upper part of the atmosphere that is predicted by climate models and is in strong disagreement with the assumption of no such moistening.
Furthermore, as Jim Hansen has argued, the current climate sensitivities predicted by the climate models are in good agreement with the best estimates of the radiative forcings and resulting temperature changes that occurred in the ice age - interglacial cycles.
All in all, the evidence that we are significantly changing the earth’s climate and will due so quite a bit more dramatically in this century is becoming stronger and stronger. Yes, there are still many things that need to be much better understood, but that should not be allowed to undermine the message about what is in fact pretty well understood now.