18 November 2005

semiglobal warming

News in Science - Global warming models 'biased' - 17/11/2005
What's wrong?
The largest global climate models today, called Earth system simulators (ESS), are so big they can only run on supercomputers.

The first UK-based simulator showed, for example, that as warming of the atmosphere dries the Amazon, vegetation dies off and carbon is released from the trees into the atmosphere.

How will the southern hemisphere cope if ocean currents, shown here, are disrupted? Scientists say we don't have enough good data to tell (Image: NOAA)Love says the Amazon has global effects on climate that are akin to 'getting hit between the eyes with a mallet', which is why climate scientists in the northern hemisphere have included it in their models.

But, he says, the Amazon is the only area in the southern hemisphere that the current models have detailed information on.The impact on climate of vegetation changes in Australia have not been modelled in detail, he says.

'Unless the vegetation change in Australia will change the climate in the UK then they are not interested,' says Love.This means current simulators are of limited use in modelling what happens at a regional level in Australia.

What about warm currents?
The scientists hope their new model will also shed more light on thermohaline circulation, which helps to deliver warm water from the south to parts of the northern hemisphere.

Current models warn that if this system collapses, due to an injection of cold water from the melting Greenland ice sheet, this could plunge places like Western Europe into a mini ice-age, like the one in the movie The Day After Tomorrow.

But, says Love, we don't know what impact such a collapse would have on the Pacific Ocean because current models lack good data on circulation in the Southern Ocean that connects the Pacific and Atlantic.

The CSIRO and the Bureau of Meteorology promise a southern hemisphere model in 2 years time. Maybe by then we will have a government that takes these things seriously.

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