New study attempts to “squeeze out” uncertainty in climate models

By Anthony Watts

Climate model uncertainties ripe to be squeezed

The latest climate models and observations offer unprecedented opportunities to reduce the remaining uncertainties in future climate change, according to a new study.

Although the human impact of recent climate change is now clear, future climate change depends on how much additional greenhouse gas is emitted by humanity and also how sensitive the Earth System is to those emissions.

Reducing uncertainty in the sensitivity of the climate to carbon dioxide emissions is necessary to work-out how much needs to be done to reduce the risk of dangerous climate change, and to meet international climate targets.

The study, which emerged from an intense workshop at the Aspen Global Change Institute in August 2017, explains how new evaluation tools will enable a more complete comparison of models to ground-based and satellite measurements.

Produced by a team of 29 international authors, the study is published in Nature Climate Change.

Lead author Veronika Eyring, of DLR in Germany,said:

“We decided to convene a workshop at the AGCI to discuss how we can make the most of these new opportunties [sic] to take climate model evaluation to the next level”.

The agenda laid-out includes plans to make the increasing number of global climate models which are being developed worldwide, more than the sum of the parts.

One promising approach involves using all the models together to find relationships between the climate variations being observed now and future climate change.

“When considered together, the latest models and observations can significantly reduce uncertainties in key aspects of future climate change”, said workshop co-organiser Professor Peter Cox of the University of Exeter in the UK.

The new paper is motivated by a need to rapidly increase the speed of progress in dealing with climate change. It is now clear that humanity needs to reduce emissions of carbon dioxide very rapidly to avoid crashing through the global warming limits of 1.5oC and 2oC set out in the Paris agreement.

However, adapting to the climate changes that we will experience requires much more detailed information at the regional scale.

“The pieces are now in place for us to make progress on that challenging scientific problem”, explained Veronika Eyring.

From the University of Exeter via press release

The paper:

Taking climate model evaluation to the next level


Earth system models are complex and represent a large number of processes, resulting in a persistent spread across climate projections for a given future scenario. Owing to different model performances against observations and the lack of independence among models, there is now evidence that giving equal weight to each available model projection is suboptimal. This Perspective discusses newly developed tools that facilitate a more rapid and comprehensive evaluation of model simulations with observations, process-based emergent constraints that are a promising way to focus evaluation on the observations most relevant to climate projections, and advanced methods for model weighting. These approaches are needed to distil [sic] the most credible information on regional climate changes, impacts, and risks for stakeholders and policy-makers.

Fig. 1: Annual mean SST error from the CMIP5 multi-model ensemble.

Fig. 2: Schematic diagram of the workflow for CMIP Evaluation Tools running alongside the ESGF.


Fig. 3: Examples of newly developed physical and biogeochemical emergent constraints since the AR5.

Fig. 4: Model skill and independence weights for CMIP5 models evaluated over the contiguous United States/Canada domain.