Warming after carbon emissions stop depends on the starting temperature
A single peer-reviewed modelling study finds that temperature change after carbon dioxide emissions stop depends on how warm the world has already become. Low-warming experiments remain close to stable, while hotter starting states produce further warming. The results reflect competing climate-energy and carbon-uptake processes in one Earth system model rather than observations of a future year.
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Emissions stopped at different warming levels
A single peer-reviewed modelling study tested what happens when anthropogenic carbon dioxide emissions are halted at a range of global temperatures. The experiments used the UK Earth System Model, version 1.2, a computer representation of climate and the carbon cycle. Starting points ranged from 1.5 to 5 degrees of warming. The researchers then followed temperature changes after emissions stopped, separating the starting temperature from the additional warming that developed during the zero-emissions period.[1]
Hotter starting states kept warming
Temperature hardly shifted after emissions ended in the experiments beginning with 1.5–2 degrees of warming. Experiments beginning at 3–5 degrees instead showed approximately 0.4–0.6 degrees of additional warming after 150 years. Atmospheric carbon dioxide declined in all these runs because land and ocean continued absorbing carbon. A larger absolute decline at higher concentrations, however, did not yield a proportionately larger reduction in the warming influence of carbon dioxide.[1]
Energy imbalance and carbon uptake
The researchers used a simpler energy-balance model to examine the competing processes. Continued warming from the climate system’s energy imbalance opposed cooling from carbon removal by land and ocean. In the hotter experiments, land carbon uptake saturated and the remaining energy imbalance was greater. Ocean uptake persisted over the longer period but did not offset the extra warming. The response was calculated in one Earth system model, so its size and warming-level dependence still require comparison across other models.[1]
