Hurricane expert: Storms gaining intensity

Kerry Emanuel is one of the world’s leading experts on hurricanes.

Kerry Emanuel is one of the world's top experts on hurricanes
Kerry Emanuel is one of the world's top experts on hurricanes

A professor at the Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences, Emanuel is also the author of a new book titled Divine Wind: The History and Science of Hurricanes.

His scientific research, discussed in his new book, shows a startling increase in hurricane strength and duration in the world, a phenemenon he correlates to rising sea temperatures linked to global warming. interviewed him by phone in Majorca (an island of Spain), where he is currently studying the effects of hurricanes in the Mediterranean Sea.

We asked professor Emanuel about Hurricanes Rita and Katrina and the apparent increase in the frequency of high-intensity storms making landfall in the United States. You’ve studied hurricanes across the world. To what extent are these hurricanes related to climate change? Could there be other factors that are not being considered?

Kerry Emanuel: The Atlantic only accounts for 10% of global tropical cyclone activity.

It’s a small player and you don’t want to really look into a small region for a global warming signal just to see – as you’d not want to look only at the temperature in London to detect global warming.

So what you see when you look at the Atlantic is the dominance of regional natural climate phenomena in hurricane records, and so we have this oscillation. There has been an upswing since about 1995 and [this] has largely been responsible for the increased number of storms which we’ve seen since then.

When we look at the global data, we do see this increase in intensity globally, which is very strongly correlated with the ocean temperature and that is almost certainly a global warming signal. So, if you look more carefully at the Atlantic  -I think what you see in the Atlantic is a combination of [the following]:

The local oscillation on a 20-30 year time scale superimposed on a much longer time-scale global warming signal, which is hard to see in just the Atlantic because its a regional phenomenon, but its there.

On this issue of climate change, last year we had the devastating tsunami in Asia. Also, as an example, the British central city of Birmingham experienced a tornado last year – something which had never happened before.

Now, with Katrina and Rita causing havoc,  are we seeing more destructive forces in nature? What is happening?

Well, each of these [occurrences] have a different explanation. There’s not a unifying theme, unfortunately. The tsunami resulted from a very large sea-earthquake in a region that’s prone to them. And I don’t think, as tragic as it was, it wasn’t seismologically completely unexpected.

Hurricane Rita intensified at a rapidly astonishing rate

Hurricane Rita intensified at a
rapidly astonishing rate

We’ve had earthquakes of that magnitude before – fortunately they are rare –  [but] certainly no seismologist would say, ‘oh there’s a trend in these things’. It’s just a random chance, unfortunately.

And in regard to the tornadoes in England, of course there have been tornadoes since the dawn of history and for any given place like a city to be hit by a tornado – even in Oklahoma where they are much more common than in England, is a very rare occurrence.

So again, here you are seeing more than anything else the element of chance and as I mentioned before, as with hurricane’s, you have chance modulated by climate signals both natural and anthropogenic.

Is it usual to see the arrival of a category 5 Hurricane so soon after the deadly Hurricane Katrina, and in the same area – the US Gulf Coast?

No it’s pretty unusual, in fact I think there are only two other years going back 50 or a 100 years where there were two Category 5 hurricanes back-to-back in the ocean. 

And Rita has undergone an extremely rapid intensification, it’s complex to [fully understand] because any hurricane, any individual hurricane has got a large factor of chance in it, you know the atmosphere is chaotic and it is like rolling the die and the die is loaded in various ways.

And one of the ways it is loaded is that hurricanes in the Atlantic are modulated by an Atlantic-wide climate phenomenon known as “the multidecadel oscillation”, that operates on a cycle of 20 to 30 years and we were in a kind of a down part of that cycle.

In the 1970s and 80s, there were few storms and the ones that occurred generally weren’t very intense and we’ve been in an up-cycle since 1995 with many storms.

Now having said that, the landfall of an intense hurricane is still largely a matter of chance.

Before Katrina, the most destructive storm we had in the US was Hurricane Andrew and that occurred in a year of very low activity. This illustrates the important role of chance.

Why was the US government so unprepared in its initial response to Hurricane Katrina? Do you think the federal and local services are better able to handle Hurricane Rita?

I think that there is far more will in this case because of the recent Katrina experience and that’s a good thing. I think the Katrina disaster has very complex origins stemming from the culture of New Orleans to the politics of disaster management.

Water submerged much of New Orleans after Katrina hit

Water submerged much of 
New Orleans after Katrina hit

In the US, it is largely the mayor of a city – and to a lesser extent the governor of a state – who are responsible for ordering evacuations and ordering in the National Guard. The federal government could twist the levers by phoning these people and asking, are you doing [enough] about this.

But I think there was a breakdown in responsibility because no one was quite sure with Katrina who was in charge, who was going to take responsibility.

It’s a tragedy with multiple dimensions and I wish I could say there’s a simple thing or person you could blame. But there are fingers that could be pointed in a lot different directions.

Hopefully it won’t be repeated with Rita.

If hurricane intensity is increasing, could we soon see Category 6 or 7 hurricanes striking the world? What significance would they have? Would we, for example, see a dramatic rise in sea level?

What we see in the data so far is that there has been [an]increase in Category 4 and 5 hurricanes globally. That doesn’t [neccessarily] mean that you can see any effect in landfall in hurricanes [which is] what we’re worrying about of course.

Hurricane’s can make landfall at any time in their life; just after they form, or maybe just when they are about to die naturally.

This sort of randomises the signature of land-falling hurricanes. But the assignation of categories is based on, I think, a fairly arbitrary scale. There’s nothing very mathematically tidy about it.

So it’s not like every 15 knots of wind is another category. There is no current definition of category 6. But I think more broadly, are we going to see more Hurricane’s that break the records?

Even if we didn’t have climate change we might expect to see that, because if you wait long enough in a random phenomenon you are bound to break records sooner or later, or maybe climate change will hasten the time of that.

Is there anything the world can do to harness or prevent such destructive forces from affecting land and populated areas? Is there anything that science can do?

There has been serious discussion in published articles and recent journals about using the atmospheric chaos as it were, to our advantage.

A chaotic system is characterised by extreme sensitivity by all perturbation (disturbance or agitation).

This is the basis of the so-called Butterfly Effect [the theoretical idea that the flapping of a butterfly’s wings can produce a storm half way across the world].

Now science has got good enough that to some extent we can ask this question: If we desired to create some alteration in the atmosphere, and we can go back in time, what kind of butterfly – what kind of perturbation – should we introduce and just were and when?

So for example we might say, oh there’s a hurricane in the Atlantic off Florida – it’s headed for Florida – could we introduce a perturbation in the atmosphere, lets say over the Pacific ocean that would amplify, lets say over three days and change the steering currents in the atmosphere, in a way that would steer the hurricane offshore?

In principle, we can do that, that is we have the scientific know how to design such perturbations. What we lack is two things: first of all the engineering – how do we go about manufacturing such a perturbation in the atmosphere?

It doesn’t have to be large, that’s the beauty of this theory, the atmosphere itself self-amplifies the perturbation.

Then there are political problems, you know, a hurricane is steered offshore and then it hits Bermuda and ah, … somebody’s going to get sued, right?

So that all will have to be worked through, but I think this will happen sooner of later, probably not in our lifetimes.

I’m speaking to you from the Arab Gulf, where we have plenty of warm water and hurricane intensity forms over warm water. Do you think we could see Katrina type hurricanes in this region?

There are several places of concern – first of all the warmest waters in the world in terms of surface temperatures are in places like the Red Sea in the [Arabian] Gulf.

And if you could put a hurricane there, it might get fantastically intense, but fortunately, the air in general is much too dry and there’s a lack of disturbances to seat a hurricane there.

To my knowledge, there’s never been one in those regions.

Now, not far from you, in the Mediterranean which borders North Africa, there are hurricane-like storms there, about which relatively little is known and I’m here in Majorca to study those, and to look at their climatology and how they might respond to global warming.

I’d say a modest concern that every once in a while, [is that] one of these will make landfall, say in Libya, and perhaps do some damage, but there’s nothing like the tropical hurricanes we are used to.

Then of course the other place that’s of big concern to the Arab world is the Indian Ocean, which is very active in both the north and south Indian oceans, [but] we have to do a lot more research to understand what the regional factors are. There’s actually been a substantial decline in hurricane’s in north Indian Ocean over the last decade which we don’t understand. 

Future hurricanes may leadto bigger human disasters

Future hurricanes may lead
to bigger human disasters

The most deadly hurricane historically by far have been in Bangladesh and the storm of 1970 killed upwards of half a million people – they’ve estimated – if you take into account all the disease after the storm etc.

And actually it contributed as a seminal push to Bangladesh’s independence [from Pakistan] in the first place, so the lack of aid from the central Pakistan government back then was a big factor in that.

So [such an event like that again] that’s a big worry, but its nice we’ve seen a decline, but I don’t think one should extrapolate that into the future. We’d like to understand why they’ve gone down recently, its actually ironically possible that it’s because of a different kind of air pollution.

You know, there are a lot of particulates being put to the air over India, by burning and by industrial emissions and they have the tendency to absorb sunlight in the atmosphere which makes the atmosphere relatively warm and the oceans relatively cool and this is very detrimental to Hurricanes.

And what we do know is that increasing topical ocean temperatures seem to be having a very bad affect on corals for example, and that has knock-on effects to the whole ecology of the ocean.

Source: Al Jazeera

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