It’s going to get worse

The worst predictions about climate change over the years have been the most accurate, according to American scientists. Temperatures are very likely to rise by over 4 degrees Celsius before the end of the century. John Dyer reports from Boston.

A new study shows there is a 93 per cent likelihood that global temperatures will rise by 4 C by 2100. (Image credit: Rich via Flickr)

The findings of a recent study indicate that researchers, policymakers, corporate executives, and even environmentalists might be downplaying the coming catastrophes that face the planet due to humankind increasing levels of carbon dioxide and other greenhouse gases in the atmosphere.

Patrick Brown and Ken Caldeira of the Carnegie Institution for Science in Stanford, California surveyed recent climate change models that analyse the effects of carbon emissions on weather.

No consensus

Those studies suggest that global temperatures will increase from 3.2 to 5.9 degrees Celsius above preindustrial levels by the end of the century if humankind takes no action to curb emissions – a scenario climate change experts call “business as usual.”

But the difference between the top and bottom of the range of projected temperature rise under a business-as-usual forecast suggests that researchers could be more skilful in tracking climate change.

“There are dozens of prominent global climate models and they all project different amounts of global warming for a given change in greenhouse gas concentrations,” said Brown in a statement. “There is not a consensus on how to best model some key aspects of the climate system.”

15% higher than UN forecast

Brown and Caldeira studied climate change models and judged them according to whether or not they had correctly predicted temperature and weather patterns in the recent past. In particular, they studied satellite images and the amount of radiation that came and left the planet’s atmosphere.

They determined that global warming would likely be 0.5 C greater than most climate change scientists have assumed would occur. That’s 15 per cent more than the United Nations’ Intergovernmental Panel on Climate Change has forecast.

They also concluded that there was a 93 per cent change of temperatures increases exceeding 4 C by 2100. The current scientific consensus of the likelihood of a 4 C increase is only 62 per cent, they wrote.

Worst-case scenario more likely

An increase of that size would hasten the submergence of small islands, kill off coral reef faster than expected and result in heat waves that would produce worse droughts and wildfires.

“Our results suggest that it doesn’t make sense to dismiss the most-severe global warming projections,” Brown said. “On the contrary, if anything, we are showing that model shortcomings can be used to dismiss the least-severe projections.”

Cloud cooling

A key factor in the researchers’ findings was how models studied clouds and global warming. Some scientists have opined that clouds would reflect solar energy back into space, mitigating global warming. But those assumptions could be wrong, the researchers said.

“The models that are best able to recreate current conditions are the ones that simulate a reduction in cloud cooling in the future and thus these are the models that predict the greatest future warming,” said Brown.

Not enough models

Climate change scientists who were not involved with the study said they found it intriguing but needed to replicate its findings.

Ben Sanderson, a climatologist at the National Center for Atmospheric Research in Colorado, noted that many of the models in the Carnegie study shared the same data. One mistake or oversight in data used throughout many models that Brown and Caldeira studied could have magnified their conclusions.

“This approach is designed to find relationships between future temperatures and things we can observe today,” said Sanderson.

“The problem is we don’t have enough models to be confident that the relationships are robust. The fact that models from different institutions share components makes this problem worse, and the authors haven’t really addressed this fully.”

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