An anonymous reader shares a report: Humanity must not pass a rise of 2 degrees Celsius in global temperature from pre-industrial levels, so says the Paris climate agreement. Cross that line and the global effects of climate change start looking less like a grave situation and more like a catastrophe. The frustrating bit about studying climate change is the inherent uncertainty of it all. Predicting where it's going is a matter of mashing up thousands of variables in massive, confounding systems. But today in the journal Nature, researchers claim they've reduced the uncertainty in a key metric of climate change by 60 percent, narrowing a range of potential warming from 3C to 1.2C. And that could have implications for how the international community arrives at climate goals like it did in Paris. The metric is called equilibrium climate sensitivity, but don't let the name scare you.