London: Limiting the increase in global average temperatures to 1.5 degrees Celsius—the key goal of the Paris Climate Agreement—is still possible, but likely requires more ambitious emission reductions than those pledged so far, according to a study.
Researchers, including those from the University of Oxford in the UK, investigated the geophysical likelihood of limiting global warming to “well below two degrees Celsius above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 degrees Celsius". They found that significant emission reductions are required if we are to achieve one of the key goals of the Paris agreement, and limit the increase in global average temperatures to 1.5 degrees Celsius.
Three approaches were used to evaluate the outstanding “carbon budget"—the total amount of CO2 emissions compatible with a given global average warming - for 1.5 degrees Celsius. These include 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, the level of emissions and warming to date were taken into account. “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 degrees Celsius above pre-industrial levels," said Richard Millar, post-doctoral research fellow at Oxford University.
“Previous estimates of the remaining 1.5 degrees Celsius carbon budget based on the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment were around four times lower, so this is very good news for the achievability of the Paris targets," said professor Pierre Friedlingstein of the University of Exeter in the UK.
“The 5th Assessment did not specifically address the implications of the very ambitious 1.5 degrees Celsius goal using multiple lines of evidence as we do here. The ambition of Paris caught much of the science community by surprise," said Friedlingstein, co-author of the study published in the journal Nature Geoscience.