6 August 2020
For more than 40 years, scientists have expressed expected temperature increases as a range, generally accepted as between 1.5 and 4.5°C higher than pre-industrial levels. A new study has sharply narrowed that to between 2.6 and 4.1°C. This is known as climate sensitivity. How sensitive global temperatures are to CO2 levels are important for policy makers, and society as a whole, to act in order to mitigate the effects of climate change.
The narrower range in temperatures also shifted towards warmer outcomes. The researchers determined that there was less than a 5% chance of a temperature shift below 2°C, but a 6 to 18% chance of a higher temperature change than 4.5°C. The results mean those who undercut the seriousness of climate change have a much harder case to make now.
The paper took an innovative approach and brought together three broad fields of climate evidence: temperature records since the industrial revolution, records of prehistoric temperatures preserved in things like sediment samples and tree rings, as well as satellite observations and computer models of the climate system. None alone could determine the range, but the researchers found ways mathematically to reconcile the three disciplines to reach their conclusions.