The Big Question: Are there more hurricanes, and are they the result of global warming?

A A A


Why are we asking this now?

Because hurricanes like the one which has careered across the Caribbean and was last night striking Mexico are only formed when the surface temperature of the ocean exceeds a specific point, which is 26C.

As the oceans warm globally with climate change, much larger areas of water will exceed the threshold, and more energy will be available to power a given storm. On the face of it, therefore, the connection might seem a reasonable, even a natural one.

So is it happening already?

Some scientists have put forward fairly dramatic evidence that it may be, and this has been seized on by the environmental community as another piece of the global warming jigsaw, to impress on governments the need to act to cut back on the carbon emissions causing the climate to heat up. But other scientists resolutely dispute the proposition, and say it cannot be proved.

What is the dramatic evidence?

It came in two peer-reviewed scientific papers published within a short time of each other in the summer of 2005. They kicked off the whole hurricane-global warming argument. In fact, they caused a sensation. The first, in the journal Nature, was by Kerry Emanuel of the Massachusetts Institute of Technology, one of the world's leading hurricane researchers. Dr Emmanuel devised a new way of measuring hurricane intensity which he called the power dissipation index, and he said he could detect an increase in this which could be related to increases in sea surface temperatures over recent decades.

The second paper was by Greg Holland of the National Centre for Atmospheric Research in Boulder, Colorado, and Peter Webster of the Georgia Institute of Technology in Atlanta (published in Philosophical Transactions of the Royal Society). Holland and Webster said they had discovered a rise in the number of Atlantic hurricanes that tracked the increase in sea surface temperature related to climate change over the last century, and taking the conventional measure of hurricane strength, the Saffir-Simpson scale, they said that the number of storms that were reaching the top categories of 4 and 5 had doubled in recent decades.

And these papers caused a sensation?

They sure did. A worldwide one.

Not least because they were published in 2005, in the middle of the worst season of Atlantic hurricanes on record, which culminated in the disaster of Hurricane Katrina which hammered New Orleans so terribly in August. The 2005 season included a record 26 named storms, of which 13 grew big enough to be classified as hurricanes (so many that for the first time since 1953, when scientists started give tropical Atlantic storms names, letters of the Greek alphabet had to be used, as meteorologists had run through the original list of 21 alphabetically-ordered names. The final 2005 tropical storm was christened Epsilon.) For the environmental community the two papers were yet another devastating indictment of the lack of action on climate change, especially by the US government of George W Bush.

So is the connection proved?

Not at all. It is hotly disputed. The difficulty lies in how we use and interpret the database of records of previous storms. Before the late-Sixties and early-Seventies, there was no global satellite coverage and measurement of tropical cyclones (which is the generic term for circular tropical storms - they're hurricanes in the Atlantic, typhoons in the west Pacific and cyclones in the Indian Ocean). So the strength of some early recorded storms may have been misinterpreted - they may actually have been much stronger than we think, and thus a general increase in intensity may be an illusion. Some storms may well have not been observed at all.

Furthermore, an increase may be part of a natural cycle, rather than being caused by human activities. The leading proponent of the no-link theory, Christopher Landsea, a senior American hurricane researcher and forecaster based at the National Hurricane Centre in Miami, has published research contending that the historical hurricane database simply cannot support the claims made by Emanuel, and by Holland and Webster, in their respective papers.

Has the argument become politicised?

'Fraid so. For example, the Bush administration put forward Landsea to assert that there was no connection between Hurricane Katrina and climate change, and he is often attacked by environmentalists. But he is a serious and respected scientist and he is by no means alone in his concern that the record does not show an increase in hurricane power and strength.

One of Britain's leading experts on tropical cyclones, Julian Heming of the UK Met Office, says: "I am of the view that this issue of the historical database is a significant one, and I think we need to be cautious about deriving too many definitive conclusion from the historical records."

Is there no consensus?

Well, there is much more of a consensus between scientists about what is likely to happen in future, than about what has happened in the past or what is happening now. The supercomputer models used for climate change prediction tend to show an increase in future hurricane wind speed and rainfall if the climate continues to warm (though not in hurricane frequency). This is not generally disputed. However, it is a smaller increase than that which the two papers from 2005 claim to have detected already.

Where is the argument now?

We can give you chapter and verse on that. Last November, the World Meteorological Organisation held an International Workshop on Tropical Cyclones in Costa Rica, and at its conclusion, it issued a one-page document entitled "Summary Statement on Tropical Cyclones and Climate Change". Its first paragraph states: "Though there is evidence both for and against the existence of a detectable anthropogenic signal [signs of a human cause such as man-made global warming] in the tropical cyclone climate record to date, no firm conclusion can be made on this point."

So the jury's out?

Not quite. The fourth assessment report of the UN's Intergovernmental Panel on Climate Change, published in February this year, gives a table showing recent climatic trends. It suggests that intense tropical cyclone activity has probably increased in some regions since 1970, and under the heading "Likelihood of a human contribution to observed trend" it observes succinctly: "More likely than not."

So is climate change to blame?

Yes...

* The historical database shows a definite increase in frequency and intensity (one view)

* Supercomputer climate models unanimously predict that climate change will make hurricanes worse

* Warmer oceans contain more energy for storms

No...

* The historical database cannot be trusted to prove an increase in frequency and intensity (the other view)

* Any increase may be part of a natural cycle

* Even in a warming world, various climatic mechanisms may act to reduce increases

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Sport
David Moyes gets soaked
sport Moyes becomes latest manager to take part in the ALS challenge
Life and Style
techCould new invention save millions in healthcare bills?
Voices
A meteor streaks across the sky during the Perseid Meteor Shower at a wind farm near Bogdanci, south of Skopje, Macedonia, in the early hours of 13 August
voicesChuck Hagel and Martin Dempsey were pure Hollywood. They only needed Tom Cruise, says Robert Fisk
News
peopleEnglishman managed quintessential Hollywood restaurant Chasen's
Life and Style
food + drinkHarrods launches gourmet food qualification for staff
Arts and Entertainment
Michael Flatley prepares to bid farewell to the West End stage
danceMichael Flatley hits West End for last time alongside Team GB World champion Alice Upcott
News
Members and supporters of the lesbian, gay, bisexual, transgender (LGBT) community walk with a rainbow flag during a rally in July
i100
Life and Style
Black Ivory Coffee is made using beans plucked from elephants' waste after ingested by the animals
food + drinkFirm says it has created the "rarest" coffee in the world
Arts and Entertainment
Jamie T plays live in 2007 before going on hiatus from 2010
arts + entsSinger-songwriter will perform on the Festival Republic Stage
Life and Style
food + drinkThese simple recipes will have you refreshed within minutes
News
Jermain Defoe got loads of custard
i100
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

Business Analyst - Banking - London - £550 - £650

£550 - £650 per day: Orgtel: Business Analyst - Traded Credit Risk - Investmen...

Data Insight Manager - Marketing

£32000 - £35000 Per Annum: Clearwater People Solutions Ltd: Our client based o...

Data Centre Engineer - Linux, Redhat, Solaris, SAN, Puppet

£55000 per annum: Harrington Starr: A financial software vendor at the forefro...

.NET Developer

£600 per day: Harrington Starr: .NET Developer C#, WPF,BLL, MSMQ, SQL, GIT, SQ...

Day In a Page

All this talk of an ‘apocalyptic’ threat is simply childish

Robert Fisk: All this talk of an ‘apocalyptic’ threat is simply childish

Chuck Hagel and Martin Dempsey were pure Hollywood. They only needed Tom Cruise
Mafia Dons: is the Camorra in control of the Granite City?

Mafia Dons: is the Camorra in control of the Granite City?

So claims an EU report which points to the Italian Mob’s alleged grip on everything from public works to property
Emmys look set to overhaul the Oscars as Hollywood’s prize draw

Emmys look set to overhaul the Oscars as Hollywood’s prize draw

Once the poor relation, the awards show now has the top stars and boasts the best drama
French connection: After 1,300 years, there’s a bridge to Mont Saint-Michel

French connection: After 1,300 years, there’s a bridge to Mont Saint-Michel

The ugly causeway is being dismantled, an elegant connection erected in its place. So everyone’s happy, right?
Radio 1 to hire 'YouTube-famous' vloggers to broadcast online

Radio 1’s new top ten

The ‘vloggers’ signed up to find twentysomething audience
David Abraham: Big ideas for the small screen

David Abraham: Big ideas for the small screen

A blistering attack on US influence on British television has lifted the savvy head of Channel 4 out of the shadows
Air strikes? Talk of God? Obama is following the jihadists’ script

Air strikes? Talk of God? Obama is following the jihadists’ script

The President came the nearest he has come yet to rivalling George W Bush’s gormless reaction to 9/11 , says Robert Fisk
Ebola outbreak: Billy Graham’s son declares righteous war on the virus

Billy Graham’s son declares righteous war on Ebola

A Christian charity’s efforts to save missionaries trapped in Africa by the crisis have been justifiably praised. But doubts remain about its evangelical motives
Jeremy Clarkson 'does not see a problem' with his racist language on Top Gear, says BBC

Not even Jeremy Clarkson is bigger than the BBC, says TV boss

Corporation’s head of television confirms ‘Top Gear’ host was warned about racist language
Nick Clegg the movie: Channel 4 to air Coalition drama showing Lib Dem leader's rise

Nick Clegg the movie

Channel 4 to air Coalition drama showing Lib Dem leader's rise
Philip Larkin: Misogynist, racist, miserable? Or caring, playful man who lived for others?

Philip Larkin: What will survive of him?

Larkin's reputation has taken a knocking. But a new book by James Booth argues that the poet was affectionate, witty, entertaining and kind, as hitherto unseen letters, sketches and 'selfies' reveal
Madame Tussauds has shown off its Beyoncé waxwork in Regent's Park - but why is the tourist attraction still pulling in the crowds?

Waxing lyrical

Madame Tussauds has shown off its Beyoncé waxwork in Regent's Park - but why is the tourist attraction still pulling in the crowds?
Texas forensic astronomer finally pinpoints the exact birth of impressionism

Revealed (to the minute)

The precise time when impressionism was born
From slow-roasted to sugar-cured: how to make the most of the British tomato season

Make the most of British tomatoes

The British crop is at its tastiest and most abundant. Sudi Pigott shares her favourite recipes
10 best men's skincare products

Face it: 10 best men's skincare products

Oscar Quine cleanses, tones and moisturises to find skin-savers blokes will be proud to display on the bathroom shelf