Graphic is excerpted from an excellent visualization at Axios.com, shows all Atlantic hurricane intensities from 2003-2015. Category five storms are highlighted and named. It illustrates the peculiar feast/famine pattern of hurricanes that makes statistical inference difficult.
After a worst case storm hits Houston another seems to be aiming for Miami. A worst case storm for Miami could be very bad indeed. I've seen a trillion dollars in possible damages bandied around - that would set the whole country back. (*) It almost seems as if a malign force is aiming hurricanes so as to do the most possible damage. It's weird and maybe karmic, as if Neptune were hurling his trident against his newly discovered enemies. It's the stuff of nightmares.
But is it really the "climate change wake-up call" that some people are claiming?
I think a lot of people have been far too quick and adamant about the climate change connection to Harvey. The main impact feature of Harvey was its slowness to advance, and its remaining parked near enough to shore to keep drawing on Gulf moisture. While impressive, Harvey was not a record-setting storm before it landed, and the factors that made it memorable don't seem all that directly related to climate.
Of course, Harvey is an instance of the changed climate; there's no disputing it was *affected* by the changed climate. Everything is, nice days as well as bad ones.
It's natural to ask whether a given extreme event was more representative of the changed climate than a comparable event would be in an unchanged climate. But that doesn't mean that science can provide a good answer.
Harvey, basically, was a Category 3 storm at landfall, Category 4 at peak, and it met an atmosphere where there were no strong steering winds just after it landed. I don't see any reason this is impossible under an unchanged climate. Is it more likely under the changed climate? Maybe. Perhaps it's slightly more likely than not. But I don't think there is an especially strong case that it is definitely so.
Beyond that, I object to the formulation "Hurricane Harvey was not caused by climate change but was made worse by it". So what do some scientists mean when they say that so unequivocally?
The context is a rather uncertain expectation that tropical storms will remain about as common as in the undisturbed climate or perhaps slightly more rare, but that the more vigourous among them will become stronger than in the past. There is weak observational evidence for these claims, but the theory and modeling is clear about a raised "speed limit".
When the public asks about attribution of specific events, the old habit of the scientific community of saying "you cannot attribute individual events to a changed climate" has been replaced by a weird sort of fractional attribution. "Rainfall in strong events is expected to go up X per cent, and this is a strong event, so X per cent of the rainfall is attributable to climate change."
I don't think this makes any sense, and it leads people to conclude things like "To be clear, Hurricane Harvey would have formed over the western Gulf of Mexico and wreaked havoc on Texas, regardless of a warming climate" which doesn't actually make any sense. This was written by Paul Douglas, a meteorologist, and I'm afraid it indicates an alarming lack of understanding of fluid dynamics.
If the proverbial butterfly can change the weather, (small perturbations lead to vastly different weather states) a trillion tons of CO2 certainly will. You just can't compare scenarios like that.
No, causality is conceptually an all-or-nothing thing. We don't want to say "Harvey was caused 99% by nature and 1% by humans" or even worse "Harvey was caused 101% by nature and -1% by humans". Nobody will understand this, and I think that is not because they don't understand the subtleties of scientific statistics, but because it makes no sense.
Does it really make more sense to say "Harvey was not caused by anything in particular but climate change made it rain 5% harder?" I am finding this just as hard to make sense of. Five per cent harder than what? Than that other Harvey that couldn't have formed in that other climate?
To be fair, it does make some sense to talk about storm surge riding on top of sea level rise. I think it's easy to see how a 12 foot surge on top of a foot of recent sea level rise is a lot like (though not exactly like) a 13 foot surge in a more stable climate. So sea level rise makes storm surge worse in a measurable way. I get that. It's worse than if sea level hadn't risen rapidly. And this matters to Rockport and Corpus Christi. But it doesn't matter to Houston, which was the main story.
The thermodynamic state of the atmosphere and ocean are all an intrinsic part of "this" storm. If there were a storm with 5% less rain, it would be a different storm in the first place. So I just don't get "made Harvey worse". If Harvey were less bad, it wouldn't be Harvey. These events are unique and distinctive. That's why we give them names.
It reminds me of the German aphorism my parents were fond of, "If my grandmother had wheels she would have been a bus."
"If Harvey weren't Harvey, it would be 5% weaker" just doesn't add up to a sensible claim to me.
==
What we really ought to be doing is seeing where the statistics of tropical storms are heading. If Harvey is part of a trend, to increasing storms, or increasing stalling, or whatever, we could say that. At least that's a well-formed claim.
But can we even say that?
The evidence is rather equivocal. NOAA says:
It is premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming–have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. That said, human activities may have already caused changes that are not yet detectable due to the small magnitude of the changes or observational limitations, or are not yet confidently modeledYes, they also say:
There are better than even odds that anthropogenic warming over the next century will lead to an increase in the occurrence of very intense tropical cyclone in some basins–an increase that would be substantially larger in percentage terms than the 2-11% increase in the average storm intensity. This increase in intense storm occurrence is projected despite a likely decrease (or little change) in the global numbers of all tropical cyclones.But that's a long way from "global warming definitely made Harvey worse".
See for yourself. There's an excellent chart that shows what the Atlantic has been doing hurricane-wise, here (excerpted and linked at the top of this article as well). Do you see an unambiguous trend? Or do you see a remarkably noisy and peculiar pattern about which it is hard to generalize?
===
So why all this talk of hurricanes? It's obvious. It's a news hook.
Climate change is very serious. Hurricanes are very serious. They're not unrelated, of course, but the relationship is complicated and as yet unclear. Claiming that "climate change made Harvey worse" is not a good look for climate science. It doesn't make semantic sense, and even if translated into terms that do, it's not a slam dunk that it's true.
Climate change is a very serious problem even if tropical storms go away altogether.
The linkage has already caused damage to the reputation of climate activism, as it was much touted in 2005, after which Atlantic hurricanes promptly subsided. People remember this. Going for a remake is not a good idea when the original movie wasn't any good.
I've been criticized for "not being a team player" on this matter. That's too bad. I really hate going against my friends and allies, and it has costs for me. But as far as I'm concerned, the way the Harvey and climate story has been told is not something I am buying into.
Our job as communicators of science is to tell people the scary truth, not just to scare people.
===
(*) (Fortunately for my peace of mind though a bit unfortunately for my catchy opening paragraph, as I finish writing this Irma is trending a bit west, which would be quite a bit less disastrous overall, though that's little compensation for the Southwest coast of Florida and the Keys, or Cuba.)
===
UPDATE: Phil Plait does a good job taking up the contrary position. But again I don't think it applies to Harvey very well.
===
UPDATE 2: Scott Denning makes a point on Twitter that I had also made earlier this week: that the language "climate change causes weather event X" is very confusing to the public regarding the relationship between weather and climate. Climate doesn't cause weather - climate is made up of weather. This point is a bit pedantic, admittedly. There's a conceptual underpinning here that, true or not, seems to need a coherent phrasing. But the problem that this phrasing is much like saying "the base hit was caused by the batter's improved batting average". In baseball you say "he's hitting well these days" or something. Then you can talk about his improved statistics. But you don't say the statistics caused the hit. The trouble is, I am having trouble formulating a clean way to say what is trying to be said.
For instance, I'm fine with making a connection between anthropogenic climate disruption and the forest fires now raging in the northwest US and western Canada. But I'm struggling with how to make the case clearly without mangling the language.
===
BACKPEDAL: Really, I think the case for a climate disruption footprint on Irma is rather stronger than that for Harvey.
32 comments:
Would you be so kind as to add a legend for your graph. X axis scale? Y axis scale? What do the colors, widths and heights of the icons represent? Do you have older data? Can you plot 2017? Thanks, Don
That was a good read! Thanks mt! One point of note: "The linkage has already caused damage to the reputation of climate activism, as it was much touted in 2005, after which Atlantic hurricanes promptly subsided. People remember this."
By "people" do you mean the proverbial median on the bell curve? If so, I'm not too sure about that...
Don, please follow the link. This is not my work.
I think it's fairly clear to anyone who has a strong interest in Hurricanes what the graph shows. I added a caption to make it more clear. But you're best off looking at the whole thing at the link which I'll repeat here yet again:
https://www.axios.com/a-history-of-atlantic-hurricanes-2482247577.html
Kau, yeah, good point!
But some people remember.
Anyway I see no reason to risk a rerun of that fiasco, though I suppose that horse left the barn a while ago.
Do I have to hope that bad hurricanes keep happening now?
Let me hasten to add that this Cato piece that Newspeak ran is worthless garbage.
http://www.newsweek.com/dont-blame-hurricanes-irma-and-harvey-climate-change-661870
I would suggest the entire "climate change causes weather event X" is ridiculous. Climate Change is merely a result! Global warming is the cause!
Yet it constantly gets bandied about as thought it were the cause of the general weirding of weather that we're witnessing, nicely removed from acknowledge the real DRIVER - manmade global warming.
I believe every climate science writer ought repeat a hundred times:
Manmade Global Warming Drives Climate Change!
Beginning the dialogue by avoiding the upfront reality that it is Global Warming driving these changes, condemns the following discussion to varying levels of disconnect, that do nothing to inform people about what we've done to our climate system, and what we had better start expecting.
~ ~ ~!
I tried hard to make sense of what you say:
"Climate change is very serious. Hurricanes are very serious. They're not unrelated, of course, but the relationship is complicated and as yet unclear. Claiming that "climate change made Harvey worse" is not a good look for climate science."
But, it doesn't compute.
The relationship unclear?
* Global warming is definitely directly related to that hot Gulf of Mexico waters that fed an explosive intensification of a tropical storm.
* Global warming is definitely directly related to the fact that the atmosphere is holding more moisture and making it available for storm systems such as Harvey to collect and dump.
* Global warming is definitely directly related to the fact that our Jet Stream has gotten weirder and is currently causing the stalling and reversal of Harvey’s northward movement.
* Global warming is definitely directly related to the fact that sea level is rising and thus adding substantially to damaging storm surges.
* Global warming is definitely directly related the Brown Ocean Effect that continued feeding moisture, energy into Harvey after it made land fall.
What about the role of hurricanes to help move access heat from tropical regions towards polar regions. Tropics are getting warmer than they have in human memory - how is that unrelated to the systems that circulate that heat?
It seems unfathomable that hurricanes can remain neutral, but in essence that is what you are telling people.
It's a huge disservice, it is that sort of misguided reassurance you are sending out that enable people to ignore today's brave new threats until they are days away, with warning and directions being screaming at them.
There's quite a bit that I disagree with in that, cc, but I agree with you that nomenclature is important, and that "global warming" and "climate change" are distinct concepts. I am not sure I agree that "global warming causes climate change" is the right way. As I would see it, "global warming" would be a TYPE of "climate change".
Human activity causes radiative imbalance everywhere, which in turn causes climate change among which global warming is the most obvious and predictable example.
"It seems unfathomable that hurricanes can remain neutral". I don't say that. Best indications are that hurricanes become a bit more scarce, but a larger fraction of those will become intense. What this means for a single unusual event like Harvey is not clear.
What I'm saying is that the way Harvey's extreme damage is being blamed on human climate disruption is muddled and far more uncertain than is being made out. The public will line up on two sides of this question as befits their tribal allegiance as usual. But people who know some science will be likely to find this fuzzy claim off-putting. And those people are important influencers of their tribes, or at least, ideally they should be.
The linkage has already caused damage to the reputation of climate activism, as it was much touted in 2005, after which Atlantic hurricanes promptly subsided. People remember this. Going for a remake is not a good idea when the original movie wasn't any good.
I think it is very easy to over-simplify the dynamics of how, what "people remember," affects public views on climate change.
There are many factors that go into how the public formulates opinions about climate change. "Skeptics" like to point to "it won't snow in England"-type comments and draw conclusions about their impact, but they don't actually use evidence when doing so. They do the same with "Climategate."
But one thing we know is that public opinions about climate change (at least in the US) are associated with political views. And it probably isn't coincidence that views about the "damage" done to the reputation of climate activism is likewise in line with political orientation.
Views on climate change are probably strongly affected by the economic state of the country (in line with a lot of evidence about concern about environmental issues more generally). They are probably strongly affected by the weather yesterday, or last month, or last winter, or last year. They are strongly affected by biases in how people approach long-term, relatively low probability risks.
Perhaps predictions about future hurricane activity after Katrina had a long-term signal on public opinions on climate change, but a precise measure, and perhaps more importantly the direction of impact, seems to me to be extremely hard to detect. How many people will be dismissive of climate change as a result, how many will still think of Katrina as a wake up call on climate change? But more importantly, how likely is it that anyone changed their minds as a result? My guess is that many people who say that claims about Katrina damaged their views on climate activism are just using claims about Katrina to reinforce preexisting views.
Trying to hedge against climate change skepticism by navel-gazing about the potential damage of claims that may turn out to be wrong seems rather misdirected, IMO. My guess is that claims that turn out to be wrong have a relatively minor effect.
On the other hand, for largely the same reasons, I also think that it's easy to overestimate the power of warnings about the links between extreme weather and climate change to increase support for mitigation policies. IMO, evidence shows that such warnings don't have much impact at this point either way.
Joshua, yeah, this is conventional wisdom in some quarters. It doesn't matter what we say, so we might as well say anything.
This pretty much overturns the social contract between society and science, though. And inpractice it dooms us to a tug of war between competing delusional systems. So I don't like it much.
How about "when I set the teakettle dial to 9, it will boil over and spatter the counter; if I set it to 8, it will simmer steadily without overflowing"
Isn't the amount of heat in the ocean surface water the difference that's attributable to climate change?
Hank, all else equal, yes, but all else is not reasonably construed as equal, and that's what makes the claim problematic.
MT writes: "As I would see it, "global warming" would be a TYPE of "climate change"."
What does that even mean?
Here's my understanding:
Mankind is radically increasing our atmospheric CO2/GHG concentrations - CO2/GHGs increase our atmosphere's insulating ability.
The sun is remaining very constant.
This causes Earth's global heat and moisture distribution engine to heat up and become more energetic and active.
Which in turn is played out by cascading climate change as we are witnessing all round us.
The way this plays out through atmospheric and oceanic circulation patterns (and hurricanes) sometimes cold Arctic air masses do get shoved into temperate realms, thus occasionally causing very short term cooling, but that's it. Over all our global climate system has been doing nothing but adding heat energy.
What in that assessment is wrong?
You can't get to second base by skipping first and all that.
Please explain circumstance that would justify putting 'climate change' in front of 'global warming'?
Here I am in southeastern Washington state and the smokers haze from the forest fires three quarters of the way around me has finally gone to trouble other folk.
Other than the usual anthropomorphic factors such as the Smoky the Bear tendency to put out every small fire so that once in awhile we have great big ones, there is the weather for the past nine or ten months. Specifically, an unusually wet winter and spring followed by three months, so far, of no precipitation. Maybe that is the result of Rossby wave slowdown, occasioned by the lesser temperature gradient between equator and the poles.
Maybe. Big dries have happened before as have big wets. Its just that I haven't experienced this extreme in my 47 years here.
"Phil Plait does a good job taking up the contrary position. But again I don't think it applies to Harvey very well."
Why can't his simple formulation apply? "What scientists are also saying is that climate change affects how hurricanes form and how they behave. This isn’t speculation, it’s inevitable. Hurricanes feed off warm water — it’s literally the source of their energy. If the water is warmer, there’s more energy to be tapped, and waters are definitely warmer now than they used to be. So is air, and warmer air holds more moisture, so there’s more rain."
That simple case for "climate change likely makes any hurrican worse" seems fine...? He goes on to say wind shear may be affecting the number, but does this really matter for discussing specific instances?
Really contrived analogy: you're wearing an armoured suit and a robot machine gun randomly fires bullets at you at some speed x + e. At the moment your armour will protect you but slightly higher velocity bullets could get through. Its wiring is such that if [arbitrary environmental condition] changes (a) the firing pattern is altered unpredictably and (b) x increases or standard deviation increases or both. The important thing here seems to be "how likely is it that any single bullet will penetrate the armour"? We know unequivocally it's more likely when the condition changes. Arguments about whether the bullet that eventually kills you would have been fired in some counter-factual universe seem irrelevant.
Convoluted way to get to the point: isn't it OK to say "x hurricane is likely to be more powerful because of simple climate physics" without having to also discuss initial conditions / chaos / counter-factuals etc? Not to say discussing hurricane formation and frequency isn't important, but they're conceptually separable without doing too much harm to logic?
I saw a chart that showed acceptance of ACC is growing at 2% per year in the US, irrespective of Katrina, Sandy, Harvey or Irma events. So maybe it does not matter much - denial is dying a slow, agonising death, and nothing will hasten it along. By the way, maybe science communication has been working better that we thought.
Just to add that the chart is inconclusive. During some of the Atlantic quiet years, the Pacific had some massive storms like Haiyan. Links with ENSO could also be usefully explored.
Stout made much the same point, back in the day. It feels like we went through this with Katrina, like, no, we can't say global warming caused it or made it worse, the argument''s more statistical.
Also, leading with the scientifically weakest, or more dubious, claim only empowers people like Judith Curry. I actually think it's a scary sign if any of the storms, including Irma, shows a global warming footprint, and it would be shocking if most of them did, already.
I've been thinking about this myself, as you may know. It seems that a key issue is how to discuss this publicly in a way that is accurate but that doesn't end up over-complicating what is being said. Some thoughts, which shouldn't be seen as my definitive view.
Given that we've changed the climate, we can't assume that these events would have happened anyway and that they're just a bit stronger than they would otherwise have been. The system is so complex that the changes we've induced means that even the pattern of events would be different. However, I do think that counter-factuals are still fine. I see nothing fundamentally wrong with saying something like "if this event had happened in the absence of anthropogenically-driven warming, it would probably have been weaker/less intense" (or something suitable). I do think that the "probably" is important, though.
The other thing that I think is acceptable is to discuss what we expect to happen and how individual events might illustrate the resulting risks. For example, even though a strong Tropical Cyclone cannot be attributed to anthropopgenic influences, we can still say that we expect an increase in the intensity and frequency of strong TCs and, hence, would expect an increase in how much damage these events could do. Hence, I think it is acceptable to discuss the impact of these events in the context of climate change.
Just some thoughts, which I'm still mulling over myself.
" Really, I think the case for a climate disruption footprint on Irma is rather stronger than that for Harvey."
And yet, the pattern of increased single-day precipitation events in the continental USA from 1910 to 2015 looks exactly like Mann's hockey stick:
https://www.epa.gov/sites/production/files/styles/large/public/2016-07/heavy-precip-download1-2016.png
Harvey's incredible rainfall is what has damaged Houston, and that story seems to fit quite nicely with AGW's effect on increasing sea and land temperatures, increasing dissolved water content. The laggy Jet Stream, due to differential polar warming, seems to have played a significant role in the devastation that was Harvey.
While US-landed hurricane wind speed and duration does not make for a compelling case for a AGW contribution, perhaps that simply means they are not the parameters to be looking at.
"While US-landed hurricane wind speed and duration does not make for a compelling case for a AGW contribution, perhaps that simply means they are not the parameters to be looking at."
Indeed. My point exactly.
Toby: " So maybe it does not matter much - denial is dying a slow, agonising death, and nothing will hasten it along."
Indeed, the victory over climate change denial is inevitable, because reality bites. The less convincing science is now, the more convincing the actual real world will be later.
It would be best to avoid having the real world do the convincing.
Toby: "the chart is inconclusive"
Zet ees exectly wheut I said, to quote Inspector Clouseau.
David, please note: I am not saying no event has an anthropogenic climate change footprint. I am saying it is a stronger case on some occasions than others.
That said, causality is always awkward.
citizenschallenge, your summary is not bad at all. There are some points of nuance I'd argue with, but I could wish that most people had this clear a grasp of the situation.
That said, surface temperature is certainly part of climate, so global warming is a type of climate change, at least in the way I've seen the phrases used by scientists.
The press seems to think they mean the same thing and can be used interchangeably. There's a style guide out there somewhere that says so explicitly. (This drives me crazy.)
Your usage matches neither of these common forms.
Whether global warming causes other types of climate change or whether it best construed as inextricably part of the same process is something I've seen argued both ways. I'm not sure if it makes much practical difference, but to me the latter formulation makes more sense.
"...causality is always awkward"
Indeed, and I'd argue that using cyclonic parameters is one of the most awkward ways of determining human emissions as a causality for climate phenomena. It's the nature of the beast - their frequencies and sizes are to an appreciable extent constrained by the physics of an Earth-like Earth (to torture a tautology), and their inherent variability sans human emissions mean that one needs much more than a thirty year sampling period (or in lieu of that, a control planet) to detect any human impact.
As many above and elsewhere have noted physics necessarily dictates that we've had an effect, even if we don't have the statistical power to yet detect it, and other metrics certainly show much more clearly how humanity has affected the climate. The thing that will sooner or later bite us is how these changes integrate to impact on our financial and/or ecological economies. People seem to thing that there'd be a long, slow trajectory from economic Nirvana to collapse, and that at some point on that tidy sliding scale we could say "OK, it's a bit rough now, we'll get our shit together and sort out the problems," when in fact a catastrophic transition between phases may be subtle and statistically imperceptible for quite a period of time around the tipping point(s).
And locked in long before then...
To bring it back to the hurricane example, the cost of clean up after Irma was today touted on radio reports as being in excess of $100 billion. That's the cost of one extreme climate event. What change in frequency of such events (on top of the cost of increase in other climate extremes) can the US shoulder before the cost of responding to hurricanes becomes unbearable? And would that unbearability come after just one final big hurricane too many? What would that unbearability look like in its unfolding, and would the milieu of the USA's climate have looked much different statistically-speaking in the near-term lead-up compared to, say, the 30 years before now?
This is evil crap:
http://www.investors.com/politics/editorials/no-michael-mann-global-warming-didnt-cause-hurricane-harveys-devastation/
I disagree with Mike about how to communicate about hurricanes and climate change. I hope I am allowed to do that without being seen as party to this contemptible, malign and fundamentally dishonest sort of character assassination that he has been subject to over his entire career, just for being a coauthor on the first hockey stick paper.
(Worth noting that Richard Muller, quoted in that contemptible piece of garbage article, Muller who has never properly apologized to Mike, has since published hockey stick papers of his own. Unlikely that readers of that article would know that.)
I've disagreed with Mike in the past on science communication, and probably will again, but I have no doubt about his rigour, honesty, and competence as a scientist. His productivity under the bizarre adverse conditions that have surrounded his career is a remarkable and impressive achievement, and my hat is off to him as far as that goes.
MT writes: “That said, surface temperature is certainly part of climate, so global warming is a type of climate change, at least in the way I've seen the phrases used by scientists.
Why have the oceans disappeared from this equation? It’s global warming, and it involves the entire global system - Surface, cryososhere, oceans, atmosphere.
Are you saying that is wrong?
~~~~~~~~~~~~~~~~~~
MT writes: “That said, surface temperature is certainly part of climate, so global warming is a type of climate change, at least in the way I've seen the phrases used by scientists.”
The press seems to think they mean the same thing and can be used interchangeably. There's a style guide out there somewhere that says so explicitly. (This drives me crazy.)”
I’ll bet not near as much this epic example of contrarian driven SEEPAGE drives me crazy.
Yes, scientists and the press seem to have decided out of political expediency a long time ago that it would be more calming for scientists to use climate change. It was a hideous mistake and another key to why the public dialogue has been driven into the gutter since about the Reagan Administration and their concerted attacks on science.
~~~~~~~~~~~~~~~~~~
As for your comment re the Mann bashing Investors.com article - glad it bothers you.
It starts with seepage and before one knows it, one is aiding and abetting without even recognizing it.
Please think about it.
Consider Mann and “his” hockey stick.
All it takes is a closer reading of those two early Mann et al hockey stick papers to appreciate Mc/Mc were trumping up a con job. It was clearly a pioneering ground breaking piece of science, it never claimed to be perfect, it even recognized some of its own weaknesses. It was part of a work in progress that's continued produced ever more exacting results in subsequence years with increase data and analysis.
Mc/Mc final "corrected" adjustments made almost no difference to the overall shape of that graph.
If I'm wrong about my assessment someone let me know. If I'm not wrong, it's an indictment of the entire scientific community that no one could convey that simple truth to leaders and the public.
~~~~~
Once again Climate Change is a result that is driven Global Warming!
Climate Changes we are observing are a result of Global Warming.
Here on this Earth in this time, it’s never, ever the other way around! That not my opinion, that’s physics. If I’m wrong it should be easy enough to show me some examples and a better explanation than what's been offer in the above.
Please excuse me if a little attitude peeks though, but I’ve been spending the past half century watching us turning our wonderful cornucopia planet into a wasteland, while most scientists present their work as thought it’s nothing more than another ‘interesting problem’ and that all it’s beauty is in it’s complexity of uncertainties - rather than in figuring our how to convey the truth of our living climate system to nonscientist. As a science loving, living human it drives me up the wall - because the fundamentals are so simple, consistent and beautiful.
reposted from Eli's in response to a commenter saying "But once a hurricane has started, the amount of energy it expends becomes a much simpler matter of thermodynamics. To stretch the metaphor, many things can light a fire, but the size depends on how big the pile of fuel it can burn"
This seems to be what is behind what has emerged as the Standard Claim:
"Global Warming did not cause hurricane H, but it certainly exacerbated it".
I have a number of points of discomfort about this claim.
Nobody sane disputes that hurricanes like warm water, and the warmer the water, the higher intensity a hurricane could conceivably attain to. But as Emanuel points out in the longer lecture, most hurricanes do not achieve that speed limit.
Note that the speed limit is a function of water temperature. Whatever the ceiling that a given storm operates under, a small fraction attain to that limit. Why?
The details are complex. But it is certainly not the case in practice that the amount of fuel available is the dominant factor in setting the maximum.
I think it is certainly the case that anthropogenic climate change causes increased sea level, and that change is for practical purpose superimposed on storm surge (modulo adaptation time scales). So sea level makes storm surge worse, and it makes sense to say that for a given storm H.
Is it the case that anthropogenic climate change exacerbated the intensity of a particular storm H?
Well, it's fair to say that the warm temperatures have an anthropogenic component; one could sensibly attribute that component to a local trend.
Can we in turn say that the ensemble of storms emerging from that environment are stronger as a result of that warming? All else equal, yes. But anthropogenic climate change affects other features of the environment. It is at least conceivable that the net of anthropgenic change makes a given storm intensity less likely. But even this claim is weaker than the one we are expected to support.
The claim is that "anthropogenic climate change made storm H worse". At this point I am at a loss for a counterargument because in the event that storm H did not attain to its speed limit, we don't have any way of comparing storm H to a counterfactual identical storm H' in the undisturbed climate.
Now you may say I am hairsplitting here, but it matters, because defending this claim involves handwaving. We know the hurricane community is chock-a-block with climate change grumblers, not to mention full-on naysayers, in the tradition of Bill Grey, who reviled the whole idea of climate change. We needn't mention Eli's nemesis by name here.
As is usual for people looking for null results, these people have a whole slew of them. And they'll defend their null with ferocity and not without ammunition. The empirical record is especially equivocal on this matter.
I have little doubt that Emanuel is right and that the physically most intense storms will be getting worse. But Harvey wasn't that.
Harvey was fairly large, and stationary over a population center. We don't have any theory about whether stationary storms increase (as far as I know; I didn't understand the size of Emanuel's ensemble. He ought to look at that, methinks.)
The promulgation, even, indeed, the unseemly told-ya-so celebration of Harvey is not polemically convincing.
The arrival of a genuine speed-limit storm hot on its heels makes the matter so much more exasperating. Irma is an example of what we can expect. We ought to talk about that. Harvey is just a grey swan, of a subspecies about which we as yet know nothing.
I looked a little at Emanuel's writeup and it is just broad brush thermodynamic arguments. It looked to me as if the thermodynamic efficiency of a cyclone is directly related to the vertical temperature gradient and not its absolute level. It would thus seem to me that the lapse rate is very important to these arguments. Will the temperature gradient increase or decrease with warming? I don't know of much evidence here. It does appear however that in fact the tropical tropospheric "hot spot" has not been as significant as predicted by models as Real Climate shows in their relevant plot of the data and models. This line of reasoning would seem to offer reasons of skepticism for GCM predictions of TC changes with warming.
http://www.realclimate.org/images//tmt_trop_trends_2016.png
In any case, it's not clear to me what the right answer is, just hoping for some clear arguments from you MT.
"efficiency of a cyclone is directly related to the vertical temperature gradient and not its absolute level"
I'm not an expert on hurricanes. My understanding of Emanuel's case is that the intensity depends on the difference in temperature between the top and the bottom. Mature hurricanes don't exist in an ambient lapse rate; they create their own lapse rate. And if anything, the temperature at the lower stratosphere is dropping, which would exacerbate the storms.
I've never been a big believer in this "missing tropospheric hot spot" business; it seems like it's noise, figuratively and literally. But even if there's a real fundamental flaw in the large scale mid-tropospheric dynamics of GCMs that is involved, I don't see how the missing physics could have more than a trivial effect on mature hurricanes.
Thanks, MT, for that. I guess I agree with your post's main point that hurricanes are not a good way to argue about global warming or climate change impacts. The data is very untrustworthy in the deep past and meaningful trends are very difficult to detect reliably. I saw something by a hurricane expert I think at Colorado State arguing that if anything the trend is flat over the last 150 years using reasonable corrections for the pre-satelite era. If one looks at peak wind speed of hurricanes for example, sampling is so much more frequent than in the past, we are much more likely to detect strong but short lived intensification. I also wonder how reliably we know wind speeds from 100 years ago. I would guess that instrumentation was much worse and may simply have broken in extreme winds.
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