June 30, 2017 – Observational records show that half a degree increase in global temperature in the recent past has resulted in substantial increases in extreme weather events, according to a commentary published today in Nature Climate Change.

Discriminating the climate impacts between warming levels of 0.5°C difference is high on the post-Paris science agenda. In their commentary, “In the observational record half a degree matters,” the scientists – Dr Carl-Friedrich Schleussner, Peter Pfleiderer, both of Climate Analytics and the Potsdam Institute of Climate Impact Research, and Dr Erich Fischer of ETH Zürich – argue that the observational record can provide useful guidance for what half a degree warming means.

“As the IPCC prepares its special report on the impacts of 1.5°C of warming in the context of the Paris Agreement, one of the pressing questions for scientists today is whether we know that limiting warming to 1.5°C instead of 2°C would make a difference in the future,” said Dr Schleussner.

“We have to rely on climate models to predict the future, but given we now have observational evidence of around 1˚C warming, we can also look at the real life impacts this warming has brought.”

The scientists looked at the changes in extreme weather events as a result of a 0.5°C warming between two periods: 1960-1979 and 1991-2010.

“The hottest summer temperatures increased by more than 1°C in a quarter of global land areas, while the coldest winter temperatures warmed by more than 2.5°C,” said Peter Pfleiderer.

Extreme precipitation intensity increased by at least 9% in a quarter of land areas. The duration of warm spells increased by about a week in half of land areas – substantially outside of the range of natural variability.

These findings give an indication of the climate impacts that could result from an additional half a degree of global warming in the future, although future impacts of additional warming will likely be higher.

“As we’re moving increasingly outside of the range of natural climate variability, we have to expect that impacts on agriculture, human and biological systems will be more pronounced,” said Dr Schleussner.

These findings may be helpful to guide our perception of 1.5°C versus 2°C.

“Communicating abstract quantities like differences in global mean temperature is difficult. With the warming the world has already experienced, we have an actual record of warming to study, and we can see very clearly that a difference of 0.5˚C of warming really does matter, ” said Dr Fischer.

Link to commentary in Nature Climate Change