A Clash Over Degrees: How Hot Should Nations Allow the Earth to Get?

At last year’s global climate talks in Glasgow, world leaders, scientists and chief executives rallied around a call to “keep 1.5 alive.”

The mantra was in reference to an aspirational goal that every government endorsed in the 2015 Paris climate agreement: try to stop global average temperatures from rising more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels. Beyond that threshold, scientists say, the risk of climate catastrophes increases significantly.

Now, 1.5 is hanging on for dear life.