How does the CMIP6 ensemble change the picture for European climate projections?


T.E. Palmer, B.B. Booth, C.F. McSweeney

Environmental Research Letters
Work Package 2



Understanding the latest climate projections is important for keeping our strategies for addressing climate change in line with the latest science. This study compares projections from the latest generation of climate models, dubbed CMIP6, with older models. The team found that the newer models project greater increases in summer temperature and reductions in summer rainfall over Europe in the future than their CMIP5 predecessors. Greater global sensitivity and, in some regions, increased regional sensitivity are behind some of these changes. This may be due to improvements in the understanding of physical processes. These results are useful for updating our strategies for mitigating and adapting to climate change, ensuring that its future impact is limited.

Climate projections are a crucial part of future planning in relation to climate change. This includes both mitigation and adaptation, which must both be considered as the impacts of climate change continue to be felt. The latest generation of climate models, dubbed CMIP6, provides the opportunity to improve our understanding of our future climate over their CMIP5 predecessors. It is, however, important to understand how projections made with these new models may differ from older ones with which current plans may have been made. This paper looks at how CMIP6 models may change the picture regarding climate projections for Europe. Understanding these changes will help people and policymakers refine strategies for mitigating and adapting to the impacts of future climate change.

The team found that CMIP6 projections differ from CMIP5 in the summer. The projections show increased warming across Europe, as well as less rainfall in parts of northern and central Europe compared to CMIP5. Central Europe and the Mediterranean see significantly higher temperature rises using CMIP6 models, indicating an increased severity of the impact of global warming. Much of this increase in temperature rise projections is down to an increased global sensitivity in CMIP6 models, however central Europe also shows higher regional sensitivity. The rainfall projections for northern and central Europe also show much less spread than the projections from CMIP5, possibly through an improved understanding of physical processes influencing rainfall. These results contribute to discussions of whether to combine CMIP5 and CMIP6 model ensembles, which may further improve projections in some cases. The latest projections also better sample some of the low likelihood, but high impact projections for Europe, and so may be better placed to inform risk-based decision making where costs are dependent on exceeding thresholds. Understanding the latest climate projections is a key part of informing effective decisions on how to mitigate and adapt to the impacts of climate change.

This study statistically compared two ensembles of climate models. The CMIP6 ensemble included 25 models, while the CMIP5 ensemble included 34. The projections from these models used the RCP8.5 scenario of future emissions, giving the strongest climate signal and therefore the clearest comparison. The projections used a baseline period of 1995-2014, and their results for two future periods (2041-2060 and 2081-2100) were compared, determining differences between the two model generations. Europe was divided into the regions of northern Europe, central Europe, and the Mediterranean to provide consistency with other international studies. The team focussed on the model results for summer (June-July-August) and winter (December-January-February).

Policy relevance
This type of comparison highlighting the changes seen in the latest generation of climate model projections is an important part of planning for climate change. Informing policymakers and communities of the latest climate projections helps inform policies aimed at reducing the impacts of future climate change. The latest projections also better sample some of the low likelihood, but high impact projections for Europe, where decisions must be made based on the risk of exceeding thresholds.


We compare CMIP6 projections for seasonal mean temperature and precipitation to CMIP5 for northern Europe, central Europe and the Mediterranean. The CMIP6 ensemble shows increased projected summer warming compared to CMIP5, which was found to be statistically significant in central Europe and the Mediterranean. Precipitation projections for Central Europe in CMIP6 were found to have a stronger drying trend in the summer months, there was also a substantially narrower projection range. Spatial comparisons indicate that this stronger drying trend also extends into a large part northern Europe. We show that warmer projected summer temperatures in northern Europe and the Mediterranean are largely driven by the higher global climate sensitivities in CMIP6 models, while regional changes are broadly similar. In central Europe a significant difference in the regional responses was found and in these cases the picture can be said to have changed. We find the difference in regional sensitivity is important in central Europe where it accounts for roughly 40% of the differences between ensembles in projected regional temperature.