Controls of the Transient Climate Response to Emissions by physical feedbacks, heat uptake and carbon cycling

  • Richard G Williams, Paulo Ceppi, Anna Katavouta
  • Environmental Research Letters, May 2020, Institute of Physics Publishing
  • DOI: 10.1088/1748-9326/ab97c9

Why do the latest climate models differ in how much surface warming increases with carbon emissions?

What is it about?

Surface warming projections increase with the cumulative amount of carbon emitted in climate models. However, there are differences in the amount of warming for a given emission of carbon in the latest suite of climate models. We identify the importance of the different factors controlling this amount of warming for a given carbon emission in these climate models. We find that intermodal differences in the climate feedbacks and heat uptake in the latest models are more important than intermodel differences in how the models take up carbon. In particular, intermodel differences in cloud feedbacks on the incoming and outgoing radiation are important in determining differences in the surface warming for a given carbon emission.

Why is it important?

We need to know how much carbon we may emit to avoid exceeding warming targets. There are differences in model projections for how much carbon may be emitted. These intermodel differences in how much carbon may be emitted are connected to radiation and thermal effects of clouds, followed by how the oceans take up heat and then finally by differences in how the land and ocean take up carbon (ordered from most to least important).


Professor Richard G Williams
University of Liverpool Department of Earth Ocean and Ecological Sciences

This work is a team effort to try unravel the reasons for differences in climate model projections. We have investigated the response of the climate models by combining expertise in clouds (Paulo Ceppi), expertise in ocean heat uptake (Ric Williams) and expertise in carbon-cycle feedback (Anna Katavouta). We have deliberately focussed on assessing the climate model responses for an idealised forcing scenario (of an annual 1% rise in atmospheric CO2) in order to gain insight into the controlling factors. The realistic climate model response may be further complicated by the effect of aerosols and the response of the carbon system to emissions.

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The following have contributed to this page: Professor Richard G Williams