The Paris Agreement set out a goal to keep global temperature rise below two degrees against pre-industrial levels. The 2°C target was first used in the 1970s by Economist William Nordhaus who believed 2°C be a tipping point where climate impacts would pass into a region previously unseen. This target has subsequently been used in other agreements, including the 1997 Kyoto Protocol which aimed to reduce global emissions, and has subsequently been adopted frequently as a target for climate policy.
The 2°C target is believed to be a tipping point beyond which the Earth’s systems will face runaway and irreversible change and impacts.
– Christiana Figueres, Mission2020