Global warming could drive world temperatures up 7 degrees by 2100

Another piece of the global warming puzzle has been revealed. According to new research published on Jan. 1 in the journal Nature, increased levels of carbon dioxide in the atmosphere will reduce the number of clouds that form. This, in turn, will cause temperatures to rise much higher than previous climate-change models have predicted.

According to this new research, global temperatures could rise 4 degrees Celsius or 7.2 degrees Fahrenheit by the year 2100, and twice that by 2200. Lead researcher Steven Sherwood at the Climate Change Research Center at Australia's University of New South Wales, told The Guardian that this level of climate change would be "catastrophic rather than simply dangerous. For example, it would make life difficult, if not impossible, in much of the tropics, and would guarantee the eventual melting of the Greenland ice sheet and some of the Antarctic ice sheet."

 In a news release, Sherwood said this new research is not an indication that previous models were wrong, only that new models are constantly improving. "Climate sceptics like to criticize climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models which predict less warming, not those that predict more."

The new model focuses on the radiative effect of clouds – in other words, how much of the sun's energy they reflect back into space – and how carbon dioxide levels will affect the activity of water vapor in the atmosphere and therefore the formation of clouds. The researchers write that water vapor follows multiple paths. Sometimes it rises many miles into the atmosphere to form reflective rain clouds. Other times the water vapor rises just a few miles before drifting back down to the surface. The new paper suggests that in a carbon-dioxide-heavy world, less water will rise to form those reflective clouds, allowing more solar radiation and heat to enter the atmosphere.

"Our research has shown climate models indicating a low temperature response to a doubling of carbon dioxide from preindustrial times are not reproducing the correct processes that lead to cloud formation," Sherwood said in the release. "When the processes are correct in the climate models the level of climate sensitivity is far higher. Previously, estimates of the sensitivity of global temperature to a doubling of carbon dioxide ranged from 1.5 degrees C to 5 degrees C. This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3 degrees C to 5 degrees C with a doubling of carbon dioxide."

Sherwood told The Guardian that this new research does not conclusively rule out the lower range of temperature rise projections, but he called on the world to "urgently start to curb our [CO2] emissions" if we hope to avoid the effects of the worst temperature rises.

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