More severe global warming predictions are likely more accurate

A street cleaner works in heavy smog in Delhi India

A street cleaner works in heavy smog in Delhi India

The latest research suggests the models that most accurately predict today's climate patterns are the ones that predict less cloud cooling in the future.

This variety of climate models is the reason long-term predictions tend to be all over the place, with some models predicting only a few degrees of warming while other models predict a lot more.

The UN's forecast for global warming is about 15 per cent too low, which means end-of-century temperatures could be 0.5 degrees Celsius higher than now predicted, said a study released Wednesday.

The United Nations' Intergovernmental Panel on Climate Change (IPCC), which provides the scientific foundation for global climate policy, projects an increase in the earth's average surface temperature of about 4.5 Celsius by 2100 if carbon pollution continues unabated.

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But there is a very large range of uncertainty - 3.2 to 5.9 degrees Celsius - around that figure, reflecting different assumptions and methods in the dozens of climate models the IPCC takes into account.

"Our study indicates that if emissions follow a commonly used business-as-usual scenario, there is a 93 per cent chance that global warming will exceed 4C by the end of this century", said Dr Ken Caldeira, an atmospheric scientist at the Carnegie Institution for Science, who co-authored the new study.

The new study, published in the journal Nature, sought to resolve this situation and establish whether the upper or lower estimates are more accurate.

"Our results suggest that it doesn't make sense to dismiss the most-severe global warming projections based on the fact that climate models are imperfect in their simulation of the current climate", Brown said.

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The researchers concluded that models which predicted bigger rises were the most likely to be accurate - with rises of 0.5C higher than previous estimates. One scientist not involved in the research described it as a "step-change advance" in the understanding of how hot our planet is likely to become.

"We are now more certain about the future climate", said William Collins, a professor of meteorology at the University of Reading. This data included the amount of sunlight reflected back into space, how much heat is leaving the Earth, and how much total energy is entering and leaving the atmosphere.

However, experts also warn that there is need for caution when predicting such complex phenomena as climate change.

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