Higher CO2 concentrations increase extreme event risk in a 1.5 °C world

• Published in: Nature climate change Vol. 8; no. 7; pp. 604 - 608
• Main Authors: Baker, Hugh S., Millar, Richard J., Karoly, David J., Beyerle, Urs, Guillod, Benoit P., Mitchell, Dann, Shiogama, Hideo, Sparrow, Sarah, Woollings, Tim, Allen, Myles R.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11-06-2018; Nature Publishing Group
• Subjects: 704/106/694/1108; 704/106/694/2739; Anthropogenic factors; Carbon budget; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Climate; Climate Change; Climate change mitigation; Climate Change/Climate Change Impacts; Climate policy; Climatic extremes; Computer simulation; Earth and Environmental Science; Emissions; Environment; Environmental Law/Policy/Ecojustice; Environmental policy; ENVIRONMENTAL SCIENCES; Environmental Sciences & Ecology; Extreme weather; Future climates; Global temperatures; Heat stress; Heat tolerance; Human influences; Iterative methods; Letter; Mean temperatures; Meteorology & Atmospheric Sciences; Mitigation; Northern Hemisphere; Precipitation; Temperature; Temperature effects; Temperature rise; Tropical climate; Upper bounds; Weather effects
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/s41558-018-0190-1

The Paris Agreement
1
aims to ‘pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels.’ However, it has been suggested that temperature targets alone are insufficient to limit the risks associated with anthropogenic emissions
2
,
3
. Here, using an ensemble of model simulations, we show that atmospheric CO
2
increase—an even more predictable consequence of emissions than global temperature increase—has a significant direct impact on Northern Hemisphere summer temperature, heat stress, and tropical precipitation extremes. Hence in an iterative climate mitigation regime aiming solely for a specific temperature goal, an unexpectedly low climate response may have corresponding ‘dangerous’ changes in extreme events. The direct impact of higher CO
2
concentrations on climate extremes therefore substantially reduces the upper bound of the carbon budget, and highlights the need to explicitly limit atmospheric CO
2
concentration when formulating allowable emissions. Thus, complementing global mean temperature goals with explicit limits on atmospheric CO
2
concentrations in future climate policy would limit the adverse effects of high-impact weather extremes.
A 1.5 °C temperature target can have varying atmospheric CO
2
concentrations associated with it. GCM simulations reveal CO
2
increases have a direct impact on climate extremes, highlighting the need for climate policy to complement temperature goals with CO
2
targets.