A temporary rise above global warming targets such as 1.5°C or 2°C could cause long lasting changes in the climate system even if global temperatures later return below those thresholds according to a new study led by researchers at Concordia University.
The research examined how different parts of the climate system respond when warming temporarily exceeds a target. Scientists used the University of Victoria Earth System Climate Model to compare 42 pairs of climate scenarios.
In each comparison, one scenario temporarily crossed a warming threshold before returning to the target pathway while the other remained below the threshold throughout.
Researchers measured the extent of warming overshoot using “degree-years”, which accounts for both how far temperatures rise above a target and how long they remain there. They found that this measure was strongly linked to persistent changes in several climate variables.
Permafrost emerged as particularly vulnerable. The study found that much of the carbon lost from permafrost showed little recovery even after temperatures returned to baseline conditions.
Other effects including sea level rise, ocean warming and changes in ocean oxygen levels also largely remained after the period of temperature overshoot ended.
The findings indicate that the maximum temperature reached is not the only factor determining long term climate impacts. The amount of time the planet spends above a warming threshold can also influence how much permanent or slow to reverse change occurs.
The researchers said the results have implications for climate policy and adaptation planning. Climate targets may need to be considered not simply as temperature limits that can be crossed and later restored but also in terms of the pathway taken to reach those temperatures.
The study was published in Nature Communications Earth & Environment. It was authored by Concordia postdoctoral fellow Mitchell Dickau, Concordia professor Damon Matthews and Simon Fraser University professor Kirsten Zickfeld.