Masters: “It appears that this year’s record [sea surface temperatures] have significantly expanded the area over which major hurricanes can exist over the Atlantic.”
"Masters: “It appears that this year’s record [sea surface temperatures] have significantly expanded the area over which major hurricanes can exist over the Atlantic.”"
2010 hurricane season has already set multiple records
A rare double feature: two simultaneous Category 4 hurricanes in the Atlantic, for only the second time in recorded history.
Uber-meteorologist and former NOAA Hurricane Hunter (!) discussed some of the remarkable records the 2010 season has already set, on his WunderBlog yesterday:
The Atlantic hurricane season of 2010 kicked into high gear this morning, with the landfall of Tropical Storm Karl in Mexico, and the simultaneous presence of two Category 4 hurricanes in the Atlantic, Igor and Julia. Tropical Storm Karl’s formation yesterday marked the fifth earliest date that an eleventh named storm of the season has formed. The only years more active this early in the season were 2005, 1995, 1936 and 1933.
This morning’s unexpected intensification of Hurricane Julia into a Category 4 storm with 135 mph winds has set a new record–Julia is now the strongest hurricane on record so far east. When one considers that earlier this year, Hurricane Earl became the fourth strongest hurricane so far north, it appears that this year’s record SSTs [sea surface temperatures] have significantly expanded the area over which major hurricanes can exist over the Atlantic.
This morning is just the second time in recorded history that two simultaneous Category 4 or stronger storms have occurred in the Atlantic. The only other occurrence was on 06 UTC September 16, 1926, when the Great Miami Hurricane and Hurricane Four were both Category 4 storms for a six-hour period. The were also two years, 1999 and 1958, when we missed having two simultaneous Category 4 hurricanes by six hours. Julia’s ascension to Category 4 status makes it the 4th Category 4 storm of the year. Only two other seasons have had as many as five Category 4 or stronger storms (2005 and 1999), so 2010 ranks in 3rd place in this statistic.
This year is also the earliest a fourth Category 4 or stronger storm has formed (though the fourth Category 4 of 1999, Hurricane Gert, formed just 3 hours later on today’s date in 1999.)
We’ve also had four Cat 4+ storms in just twenty days, which beats the previous record for shortest time span for four Cat 4+ storms to appear. The previous record was 1999, 24 days.
I don’t think there is much question that in the North Atlantic we’re going to see more intense hurricanes as humans keep warming the planet (see “Nature: Hurricanes ARE getting fiercer “” and it’s going to get much worse“).
One of the country’s foremost authorities on the subject MIT meteorologist Kerry Emanuel talked to Yale Environment 360 about the much discussed topic of the link between global warming and hurricane intensity. The bottom line is that he “says that amid the uncertainty, one thing seems likely: an increase in the most potent “” and destructive “” storms.”
Here is an extended excerpt:
Yale Environment 360: The topic of hurricanes and what might happen to them as the world warms has been a subject of great interest to you, and your position has evolved. I wanted to see what your thinking is now.
Emanuel: Let me turn the clock back to 1987 when we published the first paper on this subject, which made use of a recently developed theory that looks at the energetics of hurricanes. And it was basically that the supply of energy is evaporation of ocean water, which transfers heat from the ocean to the atmosphere. And the drain on energy is friction between the winds and the ocean surface. And that allows you to make an estimate of how strong hurricanes could get”¦It gives you an upper bound of hurricane wind speed, and the upper bound turns out to be a very good predictor of how strong hurricanes can be. And the upper bound is such that you could easily calculate how climate change of any kind affects it. We realized way back in 1987 that CO2-induced warming would increase that speed limit on hurricanes, if you will. And that was also published in Nature [in 2005], and the increase was modest but by no means negligible. The main point of that paper is that there was this fantastic relationship between ocean temperature and hurricane power”¦It surprised us how much power increase you got with just a little bit of increase in the sea surface temperature. . . .
In the 2008 paper, we had developed a technique for basically inferring hurricane activity from a coarse representation of the climate, such as you might get from a climate model”¦The main point of the paper is to show the models are all over the place. [But] there is a general consensus that on the global scale there probably will be a decrease in the frequency of storms [hurricanes].
e360: And why would that be?
Emanuel: That’s because if you go to the tropics where hurricanes form, everybody knows it’s pretty humid down where we live in the boundary layer of the atmosphere. But if you go two or three miles up, it’s actually quite dry”¦ When you try to form a disturbance in the tropics or anywhere else for that matter, if you try to get some thunderstorms together for example, the moist air from near the surface of the ocean rises into the atmosphere. This is what you see when you look at a cumulus cloud or a cumulonimbus cloud. But, when it’s dry in the middle atmosphere, some of that condensed water in the form of cloud or rain will re-evaporate into the dry air and cause a downdraft. And that downdraft brings cold, dry air down to the surface. And, it’s like pouring cold water on a fire. You know, it just basically wipes out everything that is trying to happen”¦ There is a lot of dry air in the middle atmosphere that tends to suppress their formation”¦
e360: And in a warming world you would expect more of that suppressive dry air in the middle atmosphere?
Emanuel: Yes, the middle atmosphere, in a relative sense, dries out if you warm it”¦That’s what causes there to be a decline. But there is something fighting against that, which is that the energy available for hurricanes, as we predicted in 1987, also goes up.
e360: Because of increasing sea surface temperatures?
Emanuel: Yes, basically”¦Now, the thing that we were very careful to point out in this paper is [that] the change in [hurricane] activity depends very much on whose climate model you look at. And the second thing we said, which is terribly important, is that it varies a great deal from place to place around the world. So, it may be that the global average [of hurricanes] is declining, but the Atlantic is sailing upward”¦
The other thing you should be very careful to understand if you look at hurricane damage over the last 100 years, the vast majority of damage has been done by a handful of storms that happened to be very intense when they made landfall. Category 3, 4, and 5 events have caused 80 percent of the damage in the United States.
e360: Hurricanes like Katrina?
Emanuel: Right, Rita, Andrew and so forth. The vast majority are still 1’s. The Category 1’s and 2’s are far more numerous than 3”s, 4’s, and 5’s, but they hardly do any damage at all. So, when you count events, if you say the frequency is going up, you’re basically saying the frequency of 1’s and 2’s is going up because they dominate the frequency. So it doesn’t really matter. What you really ought to care about are the 3’s, 4’s, and 5s. In just about every model simulation the frequency of those goes up in the global warming.
e360: Can you explain why?
Emanuel: So we have a bell shaped curve, and the peak of the curve is at a wind speed of 70 or 80 knots, and there’s a little tail that sticks out, at 150 knots or something. Now, what happens in climate change is that bell gets a little bit squatter but it also gets fatter. And so, if you’re looking at the middle of the distribution, you actually see a decline in the number of events. But, if you’re looking way out on the tail you see an increase in the number of events”¦So it follows that the number of 160-knot storms goes up.
e360: Just so I understand, because I realize it’s not as simple that as sea surface temperature goes up hurricanes become more frequent and more powerful. But, if you have warmer sea surface temperatures, more radiation, more heat going into the surface of the ocean, is the reason that you are likely to get more storms of that 3, 4, and 5 category simply because that greater radiation creates greater evaporation and larger storms?
Emanuel: You almost have it right. The key is to recognize that the strength of the hurricane is related to what we call the evaporation potential of the surface”¦In other words, that’s the heat balance of the upper ocean. The ocean gains heat by radiation both from the sun and infrared radiation from the atmosphere or the clouds within it. But it loses heat mostly by evaporation. And so, the greater the amount of radiation coming into the sea, the greater the rate of evaporation has to be to balance that”¦That means that you have to have a greater evaporative potential. It’s that potential that dictates hurricane wind speeds . . .
e360: Have you observed more energy in storms in recent decades?
Emanuel: Yes, especially in the Atlantic. We get into some nasty problems here of detection. And, the problem is that the Atlantic only contains about 11 percent of all the tropical cyclones on the planet, [but] is the only place where we routinely fly airplanes into hurricanes . . .
But when you look at hurricane power, it really has been going up a lot in the last 20 years or so in the Atlantic in sync with the temperature of the tropical Atlantic, which by the way is at an all-time record high right now.
e360: What’s the high right now, and how much has it gone up in recent decades?
Emanuel: Well, we have to be very specific about when and where. But in the place where hurricanes form in the tropical Atlantic “” we call it the main development region “” just averaged over August, I think, you’re talking about an average temperature of around 28 degrees Celsius”¦It’s about a half a degree centigrade [.9 Degrees F] warmer than it was a hundred years ago.
e360: And is that significant in terms of potential storm formation?
Emanuel: Here again, there’s a problem because there is a constant tendency to think, well, it’s just a function of the ocean temperature. But, as we discussed a minute ago, the ocean temperature is just a co-factor. It’s not the cause but on the other hand, it’s a very tempting thing because we can measure it and do measure it quite well. But the 2005 [Nature] paper showed that you get a lot of bang for the buck if you insist upon correlating hurricane power with ocean temperature. You know, a little bit, two-tenths of an increase, gives you a big increase in power.
e360: And globally are scientists measuring [ocean temperature increases] in the tropical regions where hurricanes form?
Emanuel: Oh, yeah. I mean, the temperature just about everywhere in the tropics is going up.
e360: By a half a degree over the last century?
Emanuel: Yeah, by a roughly similar amount over a hundred years.
e360: And I know scientists like Susan Solomon and others are saying, `You ain’t seen nothing yet because a lot of this heat in the atmosphere is going to start transferring into the ocean.’ What is your thinking about what kind of sea surface temperature increases we could be looking at in the 21st Century?
Emanuel: If you believe the global models, you’re talking about another two degrees at least of warming in the tropics.
e360: Wow, two Celsius?
Emanuel: Yes, but there are a lot of caveats”¦Hurricanes may matter themselves for the climate. In other words, there may be some feedback. We think there actually is a feedback of hurricanes on climate. And, the way that they feed back principally is by their effect on the ocean. You see, when you get a hurricane one of the things it does is churn the cold water out from the depths up to the surface, and it thereby keeps the surface of the tropical ocean cooler than it would otherwise be. Now, if you did start to see an increase in hurricane power, it’s possible that that would be negative feedback on ocean temperature. It would keep the temperatures from going up quite that much. We don’t really know how effective that might be. There is just beginning to be some work on this, but if we don’t include that effect, you’re looking at around two degrees [Celsius] additional warming.
e360: Which, according to your research and your models, has got to lead to an increase in more powerful storms?
Emanuel: Yes, most of the models in the theory suggest that the more powerful storms become more numerous, and those are the ones you worry about”¦ I think the thing that people should see as interesting is the frequency of intense events. And that sort of goes up everywhere, but it goes up very unevenly. The reasons why it doesn’t go up uniformly is because the climate is a complicated system, and there are changes in atmospheric and oceanic circulation which cause some regions to warm up more than others . . .
e360: If you talk to climate scientists. there is an expectation of a sea level rise in the next century of two feet, maybe five feet, maybe six feet. When you as a hurricane specialist contemplate those kinds of sea level rises in a place like Florida, with increased hurricane intensity, that has got to be really bad news, right?
Emanuel: Yeah, it is bad news because the two big killers in hurricanes are the storm surge “” which is basically like a tsunami but created by the winds of the hurricane rather than by an earthquake “” and freshwater flooding. If you’re talking about delta regions “” and there are lot of delta regions around the world like in Bangladesh that are heavily populated “” then you get both. You get increased water coming from the sea and increased rainfall from hurricanes, water coming down rivers. It’s bad news.
His final point about the absurdity of that what the state of Florida is doing is one I could not agree more with:
You know, the state basically has become the insurer of property in Florida. Everybody knows that a relatively small hurricane will bankrupt the [state hurricane insurance] plan, and they will all go with hat in hand to the federal government. So the rest of us will bail them out. And so we have the situation of hard-working people in factory jobs and farmers subsidizing the landowners of Palm Beach. It’s crazy.
So US taxpayers will likely pay the bill for the first major hurricane that bankrupts the state, but after that, it’ll be quite interesting to see who if anybody will insure beachfront property in Florida (or elsewhere in Hurricane Alley).
- Why future Katrinas and Gustavs will be MUCH worse at landfall, Part 2
- Why global warming means killer storms worse than Katrina and Gustav, Part 1
- Mississippi burning “” and flooding: Haley Barbour to be remembered as man who gave his state 90°F temps 5 months a year plus countless Katrinas?
- Governor Jindall of Katrina-Ravaged Louisiana Tries to Block Climate Change Regulation