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Friday, 20 July, 2001, 10:56 GMT 11:56 UK
Researchers have hot expectations
Clouds AP
The IPCC's temperature range is based on computer modelling
By BBC News Online's environment correspondent Alex Kirby in Bonn

Scientists have narrowed down the likely increase in global temperatures this century - assuming nothing is done to curb the emission of greenhouse gases.

They have refined the estimates produced by the Intergovernmental Panel on Climate Change (IPCC), and expect the rise to be between 1.7 and 4.9 degrees Celsius.


If the Kyoto Protocol, the global climate treaty, does not enter into force, this is what will happen

Dr Sarah Raper
They say they can define the probable rise more closely still with a fair degree of certainty. Their findings will cause alarm among policymakers.

The scientists are Professor Tom Wigley of the National Center for Atmospheric Research, US, and Dr Sarah Raper, of the University of East Anglia, UK.

They report their findings in the journal Science. The authors took the prediction of the IPCC's third assessment report, published earlier this year, which estimated global temperature rise from 1990 to 2100 would fall somewhere between 1.4 and 5.8 degrees C, in the absence of policies to abate climate change.

'Bold' assumptions

This prediction was appreciably higher than the IPCC's second assessment report, which had put the likely rise between 0.8 and 3.5 degrees C. The increase is explained by the inclusion of new emissions scenarios, which themselves contain scientific uncertainties.

What the IPCC did not do was to address in detail the relative likelihoods of the range of predictions it offered. The authors of the Science paper have taken its work further.

Dr Raper told BBC News Online: "For risk assessment, you need to know the probability of something happening. We were able to do this, because we could make assumptions. The IPCC couldn't, but we could ignore their consensus basis.

"They did the best they could, but we've been a bit bolder than they were able to be."

One key change she and Professor Wigley incorporated in their work was to assume much lower sulphur dioxide (SO2) levels than the IPCC researchers. SO2 has a cooling effect in the atmosphere, and lower levels would therefore suggest more warming.

'Alarming finding'

Their main conclusion is that there is a 90% probability of the temperature rise falling within the 1.7 to 4.9 degrees C range. But they think the likeliest increase, with a 50% probability, will lie between 2.4 and 3.8 degrees C.

Sun PA
The scientists have made certain assumptions about the future
For comparison, we are now about 5 degrees C warmer than in the last Ice Age just over 10,000 years ago. Dr Raper told BBC News Online: "That middle prediction indicates a big increase in temperature. Even a 1.7-degree rise would be significant.

"If the Kyoto Protocol, the global climate treaty, does not enter into force, this is what will happen. We were a bit concerned when we came up with that 2.4 to 3.8 degree figure. It is an alarming finding."

As alarming as the actual increase is the timescale over which it may occur. Although, it should be said that such a dramatic change probably has occurred before in Earth's history.

Ministerial meeting

The authors conclude: "We have shown that the very high upper-limit warming rate of about 0.5 degrees C per decade given in the third assessment report is much less likely than warmings in the center of the distribution, which are about 0.3 degrees C per decade.

"Even warming at this rate, however, is very large compared with the observed warming over the past century, and considerably larger than the rate of warming suggested in the second assessment report. In many of the scenarios considered, the rate of warming is still high at the end of the 21st Century; further warming through the 22nd Century would be virtually certain in these cases."

The publication of their report coincides with the start of the high-level political session of the talks being held here to try to salvage the Kyoto Protocol. Ministers will be seeking between 19 and 22 July to agree the treaty's workings, so that enough countries will ratify it to allow it to enter into force.

But the US, the world's biggest polluter, says it will not ratify the protocol. And it is still uncertain whether another significant emitter of greenhouse gases, Japan, will ratify it without US support. If the Japanese do not do so, there will be almost no prospect of the protocol becoming part of international law.

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The BBC's Julian Siddle
"Action needs to be taken now"
See also:

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