Abstract/Summary

In the 2015 UNFCCC Paris Agreement, article 2 expresses the target of “Holding the increase in global temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C … recognizing that this would significantly reduce the risks and impacts of climate change”1. Different interpretations of the precise meaning of the phrases ‘increase in global temperature’2 and ‘pre-industrial’3 could have large effects on mitigation requirements and corresponding social, policy and political responses. Here we suggest that levels of current global mean surface warming since pre-industrial times that are higher than those derived by Millar et al. could have been calculated using alternative, but equally valid, assumptions as the ones made by those authors.