The scientific motivation of the internationally agreed 'well below 2 °C' climate protection target: a historical perspective

The 'well below 2 °C' target was scientifically further analysed in 2000 and motivated as part of the IPCC's third assessment report in its synthesis chapter, which assessed dangerous climate change. The resulting 'burning ember' diagram indicated that beyond 2 °C warming adaptation possibilities rapidly deteriorated and vulnerabilities increased, especially for unique ecosystems and extreme events. The evidence that emerged since this assessment report, on observed climate-change impacts show that vulnerabilities nowadays likely are larger. Recently, accelerated and higher levels of sea-level rise and more frequent extreme events are reported. All these insights were likely considered in the wording (i.e. 'well below 2 °C') of the 2015 Paris Agreement.