US and European scientists make new global warming prediction

Scientists in the US and England are warning that there is a 90% probability that the global average temperature will rise between 3F and 9F (1.67 and 5°C) over the next hundred years, with a 4F to 7F (2.22 to 3.89ºC) range the most likely.

This increase is in sharp contrast to the one degree temperature rise that occurred over the last 100 years, and the experts are predicting that the earth will heat up one or two degrees by as early as 2030, but the prediction is slightly lower than that estimated by the Intergovernmental Panel on Climate Change (IPCC) in January this year (see related story).

The study is published in the 20 July issue of Science magazine. In arriving at these figures, the scientists assumed that no action was taken to curb global warming before 2100.

“We are assigning probabilities to long-term projections to aid policy makers in assessing the risks that might accompany various courses of action or non-action,” said lead author Tom Wigley of the US National Centre for Atmospheric Research in Colorado. “If all scenarios are believed to be equally likely, it’s difficult to plan.”

Earlier this year, the respected Intergovernmental Panel on Climate Change announced an estimated range of warming between 2.5F to 10.4F (3.9 to 5.78°C), well up from its 1995 estimate of 1.4F to 6.3F (0.78 to 3.33°C). It reported that “new analyses of proxy data for the northern hemisphere indicate that the increase in temperature in the 20th century is likely to have been the largest of any century during the past 1,000 years. It is also likely that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year”.

But the authors of the latest report say the probability that the earth will warm only 2.5F or reach an extreme such as 10.4F is very low.

NCAR’s Wigley and co-author Sarah Raper, of the University of East Anglia in England and the Alfred Wegener Institut for Polar and Marine Research in Germany, say that even the mid-range 4 to 7F provides a massive contrast to the last century. According to their report, “whether or not such rapid warming will occur…depends on actions taken to control climate change”.

If the earth warms rapidly and the expected impacts occur soon, even quickly-implemented attempts to bring the situation back under control would not have much success in the short term, the authors warn. “The climate’s inertia would lead to only a slow response to such efforts and guarantee that future warming would still be large,” the report says.

The latest analysis attempts to put values on uncertainties about human activities and how the climate will react to them. The authors identified key uncertainties and estimated the probability that their values would fall within defined ranges. The results of this exercise have been used to create a simplified climate model and combine the various results into probability ranges for temperature increases.

NCAR is managed by the University Corporation for Atmospheric Research, a consortium of 66 universities offering PhDs in atmospheric and related sciences.

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