Science: The ultimate weather forecast: Armed with a new supercomputer, scientists are trying to answer a critical question - is it getting warmer? Nicholas Schoon reports

Remember global warming, which threatened to simultaneously roast and flood the world our children would inherit? The threat hasn't gone away. A report soon to be published by the UN's Intergovernmental Panel on Climate Change (IPCC), an international grouping of climate scientists appointed to advise governments, will confirm that mankind is gradually altering the composition of the atmosphere, and thereby its heat balance.

The document slaps down theories which hold that volcanoes and variations in the sun's output are a far bigger influence on climate in the recent past and near future than any man-made pollution. But there remain huge, intractable uncertainties about when and where the warming will occur, how it will change rainfall and weather, how much harm it can do us. The best estimate is for an average temperature rise of between 1C and 3.5C midway through the next century.

One complication: pollution from the burning of fossil fuels is cooling large areas of the planet's surface as well as warming it. Emissions of carbon dioxide (CO2) trap heat in the atmosphere that would otherwise escape into space, but sulphate aerosol - from burning coal and gas - acts as an atmospheric heat shield.

The hope is that one day supercomputers will be able to model most of the complexity and credibly predict the fate of an increasingly polluted earth. These models are among the most awesome, grandiose and beautiful applications of computer science. Their ability to simulate the behaviour of the oceans and atmosphere over a period of centuries has greatly improved over the past 15 years, but there is far to go.

Scientists at the Hadley Centre for Climate Prediction have just taken delivery of their new Cray C90 supercomputer, also used by the Met Office for routine weather forecasting. Last month they began a series of modelling experiments which will continue through the summer. The centre, at Bracknell, Berkshire, funded by the Department of the Environment and the Met Office, is among a dozen institutes around the world up to the task. Its findings are fed to the IPCC.

Starting from around 1860, the Cray will make its own calculations of how the atmosphere and oceans have responded to gradually rising emissions of man-made greenhouse gases. It will be interesting to compare its version of worldwide weather and climate in 1994 with the reality. Then the supercomputer will march on into a future in which concentrations of 'greenhouse gases' continue to rise as the world burns more and more coal, oil and gas.

Experiments using the centre's previous supercomputer showed that after 70 years of steadily rising greenhouse gas concentrations (1 per cent extra a year) average temperatures went up by 1.5C. But this simulated global warming was highly uneven. In some places there had actually been a slight cooling (see graphic), while parts of the Arctic had warmed by 6C.

The new supercomputer's most heroic feat is to simulate the behaviour of the oceans and the atmosphere and the way they influence one another. There are complex flows of energy and water going on between the two, with the oceans slowing any warming or cooling trend in the air.

It takes the Cray one day to work through two years of simulated time. The model it runs sees the continuum of air and sea as 200,000 evenly spaced points while time is broken down into instants half an hour apart. At each of these points, for each instant, it calculates pressure, temperature, wind or current direction.

If the machine can model the natural climate reasonably well, it should be able to simulate one perturbed by pollution. The scientists factor in the heat-trapping effect of rising concentrations of CO2 and other greenhouse gases caused by decades of rampant economic and population growth.

Early supercomputer models used to let their imaginary climates establish an equilibrium, then doubled the CO2 concentration instantly and waited to see what new equilibrium was established. This was highly unrealistic, for rather than abruptly vandalising the climate system humanity is gradually corrupting it. CO2 concentrations have been rising since the 19th century, slowly at first but accelerating gradually to today's rate of half a per cent a year. On present trends, carbon dioxide levels will reach twice their pre-industrial level of 280 parts per million by around 2070.

The Hadley scientists hope to get more credible predictions by inputting this gradual, accelerating build-up of greenhouse gases which reflects recent history and the likeliest future.

They are driven to cheating by their models' imperfections. It cannot simulate some of the subtleties of energy flow between the atmosphere and oceans. For instance, its resolution is too coarse to paint a true picture of what the North Atlantic's Gulf Stream is up to. So, across the oceans' entire surface there have to be an annual cycle of 'flux corrections' which compensate for the model's errors and prevent it drifing away from what is observed in the real world.

The Hadley scientists are just beginning to model the cooling effect of aerosols. These are microscopic particles of sulphate, dust and water produced by the burning of fossil fuels as well as nature - volcanoes, sea spray, forest fires and even plankton. They appear as a haze in the lower atmosphere.

Sulphate areosol cools directly, by reflecting incoming sunlight into space, and indirectly by 'seeding' clouds and boosting the number of water droplets they contain. The clouds are then whiter and brighter and also reflect more incoming sunshine back to space.

Computer modelling of these two cooling influences is in its infancy. But they may well mask some of the global warming which has already occurred and explain why supercomputer simulations of global warming predict a greater warming to date than appears to have been the case.

Clouds, which could have a critical influence on the progress of any man-made global warming, are just as confusing. 'Things seem to be even more complicated than they were perceived to be five or 10 years ago,' Dr Tony Slingo, who heads research into cloud and aerosol problems, says.

A warmer atmosphere would probably contain more water vapour - itself a greenhouse gas - causing further warming. But more vapour could mean more clouds, which have both heating and cooling effects. They trap some of the Earth's outgoing heat radiation, but also reflect incoming sunlight, preventing solar radiation from heating the lower atmosphere and ground.

Ice clouds above 35,000ft have an overall warming effect. Dense low cloud is a coolant during daytime, as anyone who has felt the chill that follows its blotting out of the Sun will know. We need to know the fate of clouds in a warming world, but supercomputers can, as yet, give little help.

None the less, the models are becoming more accurate. Just as well, because it costs taxpayers pounds 14m a year to run the Hadley Centre. But if politicians and the public demand rapid, precise information about how the climate will change they will be disappointed.

'It's a longer term problem than we may have imagined originally, but then I would say that, wouldn't I?' Dr Slingo says.

(Photograph omitted)

News
Andy Murray with his girlfriend of nine years, Kim Sears who he has got engaged to
people

Tennis star is set to marry his long-term girlfriend, Kim Sears

News
people
Arts and Entertainment
Joel Edgerton, John Turturro and Christian Bale in Exodus: Gods and Kings
filmDirector said film would 'never have been financed' with ethnic minority actors in key roles
News
people
PROMOTED VIDEO
Sport
footballArsenal 2 Borussia Dortmund 0: And they can still top the group
Arts and Entertainment
An unseen image of Kurt Cobain at home featured in the film 'Kurt Cobain: Montage of Heck'
filmThe singers widow and former bandmates have approved project
News
Andy Murray with his girlfriend of nine years, Kim Sears who he has got engaged to
peopleWimbledon champion announces engagement to girlfriend Kim Sears
Arts and Entertainment
Jake Quickenden and Edwina Currie are joining the I'm A Celebrity...Get Me Out Of Here! camp
tv
Arts and Entertainment
George Mpanga has been shortlisted for the Critics’ Choice prize
music
News
Albert Camus (left) and Jean-Paul Sartre fell out in 1952 and did not speak again before Camus’s death
people
Arts and Entertainment
Roisin, James and Sanjay in the boardroom
tvReview: This week's failing project manager had to go
News
ebooksNow available in paperback
News
Ed Miliband visiting the Holocaust museum in Jerusalem. The Labour leader has spoken more openly of his heritage recently
newsAttacks on the Labour leader have coalesced around a sense that he is different, weird, a man apart. But are the barbs more sinister?
Arts and Entertainment
'Felfie' (2014) by Alison Jackson
photographyNew exhibition shows how female creatives are changing the way women are portrayed in advertising
News
i100
Life and Style
Fright night: the board game dates back to at least 1890
life
Environment
The vaquita is being killed by fishermen trying to catch the totoaba fish, which is prized in China
environmentJust 97 of the 'world's cutest' sea mammals remain
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Web Marketing Specialist

Negotiable: Recruitment Genius: One of the UK's leading Renewable Energy compa...

Ashdown Group: Data Warehouse & Business Intelligence Co-ordinator

£35000 per annum: Ashdown Group: Required skills include SQL querying, SSRS, u...

Ashdown Group: C#.Net Developer - C#, ASP.Net, PHP, HTML, JavaScript, CSS

£30000 - £35000 per annum: Ashdown Group: C#.Net Developer - C#, ASP.Net, HTML...

Argyll Scott International: Senior Business Analyst- Insurance

Negotiable: Argyll Scott International: Senior Business Analyst - Insurance ...

Day In a Page

Cameron, Miliband and Clegg join forces for Homeless Veterans campaign

Cameron, Miliband and Clegg join forces for Homeless Veterans campaign

It's in all our interests to look after servicemen and women who fall on hard times, say party leaders
Millionaire Sol Campbell wades into wealthy backlash against Labour's mansion tax

Sol Campbell cries foul at Labour's mansion tax

The former England defender joins Myleene Klass, Griff Rhys Jones and Melvyn Bragg in criticising proposals
Nicolas Sarkozy returns: The ex-President is preparing to fight for the leadership of France's main opposition party – but will he win big enough?

Sarkozy returns

The ex-President is preparing to fight for the leadership of France's main opposition party – but will he win big enough?
Is the criticism of Ed Miliband a coded form of anti-Semitism?

Is the criticism of Miliband anti-Semitic?

Attacks on the Labour leader have coalesced around a sense that he is different, weird, a man apart. But is the criticism more sinister?
Ouija boards are the must-have gift this Christmas, fuelled by a schlock horror film

Ouija boards are the must-have festive gift

Simon Usborne explores the appeal - and mysteries - of a century-old parlour game
There's a Good Girl exhibition: How female creatives are changing the way women are portrayed in advertising

In pictures: There's a Good Girl exhibition

The new exhibition reveals how female creatives are changing the way women are portrayed in advertising
UK firm Biscuiteers is giving cookies a makeover - from advent calendars to doll's houses

UK firm Biscuiteers is giving cookies a makeover

It worked with cupcakes, doughnuts and macarons so no wonder someone decided to revamp the humble biscuit
Can SkySaga capture the Minecraft magic?

Can SkySaga capture the Minecraft magic?

It's no surprise that the building game born in Sweden in 2009 and now played by millions, has imitators keen to construct their own mega money-spinner
The King's School is way ahead of the pack when it comes to using the latest classroom technology

Staying connected: The King's School

The school in Cambridgeshire is ahead of the pack when it comes to using the latest classroom technology. Richard Garner discovers how teachers and pupils stay connected
Christmas 2014: 23 best women's perfumes

Festively fragrant: the best women's perfumes

Give a loved one a luxe fragrance this year or treat yourself to a sensual pick-me-up
Arsenal vs Borussia Dortmund: Alex Oxlade-Chamberlain celebrates century with trademark display of speed and intuition

Arsenal vs Borussia Dortmund

The Ox celebrates century with trademark display of speed and intuition
Billy Joe Saunders vs Chris Eubank Jnr: When two worlds collide

When two worlds collide

Traveller Billy Joe Saunders did not have a pampered public-school upbringing - unlike Saturday’s opponent Chris Eubank Jnr
Homeless Veterans Christmas Appeal: Drifting and forgotten - turning lives around for ex-soldiers

Homeless Veterans Christmas Appeal: Turning lives around for ex-soldiers

Our partner charities help veterans on the brink – and get them back on their feet
Putin’s far-right ambition: Think-tank reveals how Russian President is wooing – and funding – populist parties across Europe to gain influence in the EU

Putin’s far-right ambition

Think-tank reveals how Russian President is wooing – and funding – populist parties across Europe to gain influence in the EU
Tove Jansson's Moominland: What was the inspiration for Finland's most famous family?

Escape to Moominland

What was the inspiration for Finland's most famous family?