"Limiting total CO2 emissions from the start of 2015 to beneath 240 billion tonnes of carbon (880 billion tonnes of CO2), or about 20 years' of current emissions, would likely achieve the Paris goal of limiting warming to 1.5°C above pre-industrial levels," said Richard Millar of the University of Oxford, UK.

The researchers used three approaches to evaluate the outstanding "carbon budget" for 1.5°C, they explain in a press release: re-assessing the evidence provided by complex Earth system models, new experiments with an intermediate-complexity model, and evaluating the implications of current ranges of uncertainty in climate system properties using a simple model. In all cases they took into account the level of emissions and warming to date.

"Previous estimates of the remaining 1.5°C carbon budget based on the IPCC 5th Assessment were around four times lower, so this is very good news for the achievability of the Paris targets," added Pierre Friedlingstein of the University of Exeter, UK. "The 5th Assessment did not specifically address the implications of the very ambitious 1.5°C goal using multiple lines of evidence as we do here. The ambition of Paris caught much of the science community by surprise."

Related links

Emission budgets and pathways consistent with limiting warming to 1.5 °C Richard J Millar et al 2017 Nature Geoscience