• 8 June 2016

Paris Agreement prompts climate scientists to call for urgent new experiments to distinguish between global warming at 1.5ºC and 2 ºC

Photo: Prof Jim Hall delivers a speech at the MISTRAL launch

U.S. Secretary of State John Kerry, with his two-year-old granddaughter, signs the COP21 Climate Change Agreement on behalf of the United States during a ceremony on Earth Day, 22 April 22 2016.

The Paris Agreement was signed by 177 countries on Earth Day (22 April 2016), aiming to "pursue efforts to limit the temperature increase to 1.5ºC above pre-industrial levels". However, climate scientists have been quick to recognise the paucity of information in existence on the risks associated with this level of warming and say that new and different kinds of research need to be undertaken immediately if the Intergovernmental Panel on Climate Change (IPCC) special report due in 2018 is to contain sufficient evidence to distinguish between impacts at 1.5ºC and 2ºC.

If the community do not act quickly, a new paper says, the IPCC are in danger of reporting all the negative economic impacts of achieving a 1.5ºC world, without reporting on the potential positive impacts of reduced extreme weather activity that such a scenario could bring.

The Nature Climate Change paper by the ECI's Dann Mitchell et al, including collaborators from the Universities of Oxford, Leeds and Exeter, the Met Office Hadley Centre and the National Institute for Environmental Studies, Japan, highlights the need for the climate community to refocus their research priorities in order to inform on the impacts of a 1.5ºC warmer world. A new way of performing the climate projections must be developed, because the community have largely assessed far higher CO2 scenarios.

Co-author Piers Forster, of Leeds University, says: "Policy choices need underpinning by robust research. As a science community we have concentrated on high temperature futures and have been remiss at providing the research necessary to assess the impacts of temperatures not much warmer than today's."

Such studies can be explicitly designed using large ensemble methodologies that have been tested over the last decade. Large ensembles of ten-year periods for recent observed and 1.5ºC and 2ºC warmer worlds, using projected changes in sea surface temperatures drawn from existing coupled model simulations, could directly address the differences between the two scenarios. Co-author Hideo Shiogama, of National Institute for Environmental Studies (Japan), says: "Such large ensembles allow us not only identifying differences in extreme weather due to +0.5ºC warming, but also testing linearity in responses of extreme weather to the global warming"

Lead author Dann Mitchell, of the ECI, says: "Important impacts in a 1.5ºC warmer world will be seen in changes in extreme weather. This is especially concerning for developing countries and could lead to serious health and economic problems".

The paper concludes, "For once, we have been asked a very specific question [by our policy makers], so we need a very good reason indeed not to step up and answer it".

Members of the public can get involved by running simulations on their home or work computers. Co-author Myles Allen, of Oxford University, says: "The academic community have been called into action, we are doing our part, you can do yours by running climate simulations on your home PCs. The more citizen scientists we get on board, the better our science." Sign up at www.climateprediction.net.

"For once, we have been asked a very specific question [by our policy makers], so we need a very good reason indeed not to step up and answer it."