DATE: July 24, 2017

SNIP: “The IPCC research community uses a definition of preindustrial that is likely underestimating the warming that has already taken place,” said Michael Mann, distinguished professor of atmospheric science and director, Earth System Science Center, Penn State. “That means we have less carbon to burn than we previously thought, if we are to avert the most dangerous changes in climate.”

[The researchers] found that assuming the traditional late 19th-century baseline and using the highest future emissions scenario, by the middle of this century, the temperature rise will likely be about 4 degrees C (5 degrees F). With a moderate emissions scenario, the researchers found that keeping below 2 degrees C was still unlikely. Only the most aggressive scenario for reducing carbon emissions is likely to keep the temperature rise to 2 degrees C or less.