Comparative studyModern climate models are more accurate than ever

Photo: DKRZ/MPI-M

This is how detailed modern climate models are today in simulating the weather: wind speeds (blue to red) and precipitation (green), at a resolution of one kilometer, calculated using the Hamburg ICON-Model.

How hot will it get in the Sahara, how cold in Antarctica, how mild on the North Sea coast? Climate models calculate the temperature map of the Earth. Their results feed into the reports of the Intergovernmental Panel on Climate Change, underpin political agreements such as the Paris Climate Agreement and provide the basis for concrete, regional measures to adapt to climate change. But how good are these models, really? And how have they evolved since their beginnings? 

To answer these questions, Dr. Lukas Brunner and colleagues examined a total of 176 climate models spanning the past 30 years. His finding: on average, the temperature maps produced by climate models have become significantly more accurate and reliable. "But it is impressive what was already possible thirty years ago," says the physicist. "If you take a really good model from the 1990s, its performance is actually similar to that of a mediocre model today." 
Particularly exciting is the look at the latest generation: so-called kilometer-scale models, which simulate the climate system on a grid of just five to ten kilometers. Previously, grids of around 100 kilometers were standard. This means that processes such as the formation of thunderstorm cells can now be directly simulated for the first time, rather than being approximated through statistical methods. 

One of the most important of these models has Hamburg roots. The ICON Earth system model was developed at the Max Planck Institute for Meteorology, a partner institution of CLICCS. Another model, the IFS, comes from the European Centre for Medium-Range Weather Forecasts, which works closely with Hamburg's climate research community. 

Some of the latest versions of the IFS model already come remarkably close to the observational data used to benchmark the calculations. "To put it pointedly: the modeling has caught up with our observational reality," says Brunner. The model is no longer the limiting factor – the accuracy of the observational data is. 

Each model was used to run different scenarios, and the results were then compared with actually measured values. Rather than relying on a single reference dataset, ten datasets were used comparatively to account for differences in data quality. The results revealed significant discrepancies, making clear that the assessment of model quality strongly depends on the available data. 

At the same time, the study dispels a common misconception: the trend toward ever higher resolution alone does not guarantee progress. "Simply doubling the resolution without changing anything else in the model will usually not improve the results," Brunner emphasizes. What matters is that model physics and fine-tuning are also adapted to the new resolution. 

In addition to the Cluster of Excellence CLICCS, the study involved the University of Vienna, the Max Planck Institute for Meteorology, the Alfred Wegener Institute and ETH Zurich. 

The Cluster of Excellence "Climate, Climatic Change, and Society" (CLICCS) at Universität Hamburg investigates how the climate is changing and how society and climate change interact. Its overarching questions are: Which climate futures are plausible – and how can desired climate futures be achieved? 

Link to the publication 

(This content has been translated automatically.)