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°C, a new Oxford University partnership warns.
In a collaboration involving the University of Exeter, University College London and several other national and international partners, researchers from the University of Oxford’s Environmental Change Institute (ECI) and Oxford Martin School have investigated the geophysical likelihood of limiting global warming to “well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C.”
Published in the journal Nature Geoscience, the paper concludes that limiting the increase in global average temperatures above pre-industrial levels to 1.5°C, the goal of the Paris Agreement on Climate Change, is not yet geophysically impossible, but likely requires more ambitious emission reductions than those pledged so far.
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°C; 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.
Dr Richard Millar, lead author and post-doctoral research fellow at the Oxford Martin Net Zero Carbon Investment Initiative at Oxford University, said; ‘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.’
"Previous informal estimates of the 1.5°C carbon budget based on the IPCC 5th Assessment were much lower, so this is good news for the Paris targets," adds Professor Pierre Friedlingstein of the University of Exeter, a co-author on this study and a key expert on carbon budgets for the Intergovernmental Panel on Climate Change. “The reason is that the IPCC did not specifically analyse the implications of multiple lines of evidence for these very ambitious climate goals as we do here. The ambition of Paris caught a lot of us by surprise."
"This paper shows that the Paris goals are within reach, but clarifies what the commitment to 'pursue efforts to limit the temperature increase to 1.5°C' really implies." cautions co-author Professor Michael Grubb of University College London. "Starting with the global review due next year, countries have to get out of coal and strengthen their existing targets so as to keep open the window to the Paris goals. The sooner global emissions start to fall, the lower the risk not only of major climatic disruption, but also of the economic disruption that could arise."
"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."
Dr Richard Millar
A number of articles have asserted that our recent study in Nature Geoscience indicates that global temperatures are not rising as fast as predicted by the Intergovernmental Panel on Climate Change (IPCC), and hence that action to reduce greenhouse gas emissions is no longer urgent. Both assertions are false. Our results are entirely in line with the IPCC’s 2013 prediction that temperatures in the 2020s would be 0.9-1.3 degrees above pre-industrial, as is clearly shown in our figure 2c*. What we have done is to update the implications for the amount of carbon dioxide we can still emit while expecting global temperatures to remain below the Paris Climate Agreement goal of 1.5 degrees. We find that, to likely meet the Paris goal, emission reductions would need to begin immediately and reach zero in less than 40 years time. While that is not geophysically impossible, to suggest that this means that measures to reduce greenhouse gas emissions are now unnecessary is clearly false.
*Our article includes a Figure (2c) which shows the IPCC range, our projections, and temperature of recent years.