Paris Agreement to curb climate change took off

This year saw the official launch of the first international climate change accord that calls for greenhouse gas emission controls by nearly the entire world.

That deal, the Paris Agreement, was completed in December 2015 in the French capital. This April, the accord set a record among UN pacts for having the most countries—175—sign it on the first day they could. The agreement formally took effect in early November.

But negotiations in November focused on global implementation of the Paris deal were shaken by the election of Donald Trump as U.S. President. Trump said during the campaign that he would “cancel” the Paris accord and has tapped an opponent of greenhouse gas controls as head of EPA.

In other climate action, countries this year turned to the chemical industry to lead the world away from the use of a class of potent greenhouse gases: hydrofluorocarbon (HFC) refrigerants. Under the Montreal Protocol on Substances That Deplete the Ozone Layer, negotiators in October finished a legally binding pact that calls for nations to limit the amount of HFCs they use within 12 years. Though HFCs don’t harm stratospheric ozone, they were introduced as substitutes for chemicals that erode the ozone layer and therefore fall under the purview of the Montreal protocol rather than the Paris Agreement.

Chemical makers, who back the new HFC treaty, are introducing more climate-friendly substitutes, notably hydrofluoroolefins. Some environmental activists, though, are pushing for greater use of ammonia and carbon dioxide as refrigerants.