2 degrees celsius

BERLIN -- As world leaders gather in New York for the Paris climate agreement signing ceremony, they ought to remember that now is the time to finally put some muscle behind their promises.
In the past few days here in Paris, there's been excitement about the possibility of including mention of a 1.5 degree Celsius temperature limit in the COP21 agreements, a shift from the historical limit of two degrees endorsed by most developed nations.
In the next week, millions of Americans will hear and read news stories about global warming. They'll hear that allowing global average temperatures to increase by more than 2°C would be dangerous. There's only one problem: Americans think in degrees Fahrenheit.