How many climate models are there

04.09.2019 10:48

New climate model for the Intergovernmental Panel on Climate Change

Ralf Röchert Communication and media
Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research

AWI climate model calculations for the first time on the basis of the IPCC assessment report

Climate researchers from the Alfred Wegener Institute are now supplying the database for the Intergovernmental Panel on Climate Change directly with results from their global computer modeling. The data are of particular interest because the underlying model developed at the AWI resolves the sea ice and oceans much better than conventional methods. The results are used by climate scientists and stakeholders around the world to determine the consequences of climate change for humans and nature.

How much will the earth heat up in the coming decades due to climate change? How will this change our world? These are among the most pressing questions of our time. Researchers around the world are trying to find an answer to this using climate calculation models. But the earth's climate is an extremely complex matter and it is difficult to model on supercomputers. Every climate model has its strengths and weaknesses. In order to be able to better estimate the development of the future climate, the results of many different climate models are compared with each other around the world. A comparison makes it clear which climate trend is most likely and which uncertainties are associated with the forecasts. Around 50 research institutions worldwide are involved in this complex international comparison, the so-called Coupled Model Intercomparison Project (CMIP). The project is of enormous importance because the results flow into an international database and form the basis for the new major report of the Intergovernmental Panel on Climate Change (IPCC), which will appear in 2021 - the 6th assessment report (Sixth Assessment Reports, AR6).

Only three institutions from Germany

For the first time, the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) is participating in this important international comparative project with its own model. Just a few days ago, the AWI researchers entered the first detailed results of their climate calculations in the international CMIP database. "It is something special to be one of those institutions that make an important contribution to the database for the upcoming world climate report," says meteorologist Dr. Tido Semmler, who coordinates the work in the international comparison project CMIP for the AWI. “There are only three research institutions from Germany - the Max Planck Institute for Meteorology in Hamburg, the German Aerospace Center and us.” In addition, the German Climate Computing Center (DKRZ) in Hamburg plays a central role as it is the three Provides institutions with computing time and storage space and provides support in performing the simulations and providing the data.

There is a special reason that the AWI is now taking part for the first time: the experts are using a new and so far hardly widespread method to simulate the climate - a so-called “unstructured grid”, which amounts to a small revolution in climate research. Because so far almost all research groups in the world have been working with so-called “structured grids”. The principle of these grids is easy to explain: Since the modeling of the climate worldwide is far too complex, climate researchers divide the earth and the atmosphere into grid boxes, cubes with an edge length of usually 100 kilometers. In these grid boxes, the biological, chemical and physical processes that influence the climate can be calculated with the help of supercomputers. One problem, however, is that an edge length of 100 kilometers is far too coarse to take into account important processes directly - such as the ocean vortex in the Gulf Stream, which is just a few kilometers in size, or other important ocean currents that lead to an increased exchange of heat and moisture between the atmosphere and the Lead sea. Many climate models are therefore unable to faithfully reproduce the course of the Gulf Stream. The Gulf Stream has its source in the Gulf of Mexico, migrates north along the Florida coast and then branches off to the east towards Europe. In many models, however, the current moves far too far to the north because the small eddies are not taken into account.

A network that can be adapted

A finer global grid with a mesh size of only ten kilometers or less would be ideal. This would, however, multiply the number of individual bills. Even for climate simulations that span just a few years, a mainframe would take weeks. The experts at AWI, however, have developed an alternative with the “unstructured grid”. With this grid, the grid boxes for certain selected and important areas can be reduced - about ten kilometers. While the climate for the entire globe is calculated using grid boxes of normal edge length, the flexibly adjustable grid allows you to zoom into certain areas such as the Gulf Stream. With the unstructured grid, climate modeling has now acquired a new, interesting dimension that is very important for the CMIP process.

A unique head-to-head comparison

"For climate modeling, you usually combine different models that calculate different things - for example one model that models the ocean in detail and a second that describes the processes in the atmosphere," says Tido Semmler. “The unstructured grid is used in the FESOM ocean model that we developed. For the atmosphere, on the other hand, we use a conventional structured model that was developed at the Max Planck Institute for Meteorology. ”And that makes the comparison in the context of CMIP particularly interesting: The Max Planck Institute for Meteorology also couples the atmosphere model his own ocean model based on a conventional structured grid. The colleagues from AWI, however, combine the atmospheric model with their ocean model, in which the unstructured grid works. "The CMIP partners and we are very excited about the direct comparison of these results," says Tido Semmler.

Important data for climate impact research

The results of the around 50 climate models that the AWI and the other CMIP partners are currently feeding into the international database will be used by many other scientists over the next two years. Especially those experts who deal with the consequences for humans and the habitats of the earth. These research results will in turn form the basis for the reports of the Intergovernmental Panel on Climate Change; of the 6th status report, and also the summarizing report of the Intergovernmental Panel on Climate Change, the Synthesis Report, which will primarily contain recommendations for politics.

Exemplary results from the model calculation (see graphic): The development of the global mean temperature from 1850 to 2100 according to calculations with the new AWI climate model.

The AWI climate model contains the essential natural drivers of the earth's temperature such as solar radiation, natural greenhouse gas and aerosol concentrations and volcanic aerosols. The gray line stands for the control run with these natural drivers and greenhouse gas concentrations from 1850 of 284 ppm CO2. The black lines show the historical development of the global mean temperature with increasing greenhouse gas concentrations from 1850 up to 400 ppm CO2 today, which have led to a global net warming of around 1 ° C. The colored lines show the possible future development of the global mean temperature depending on the emission scenario.

The fluctuations in the lines reflect the natural variations in the global mean temperature that exist even without the emission of greenhouse gases. In the case of the historical development (black lines) and the medium-high scenario (approx. 4 ° C warming at 871 ppm CO2 in 2100) for the future (yellow lines), several calculations were carried out to estimate the uncertainty in the results. The AWI calculations have a fluctuation range of around half a degree Celsius. It becomes clear that the various simulations provide very similar results and that the results are therefore robust.

For the low emission scenario (445 ppm CO2 in 2100), strong efforts must be made to reduce greenhouse gas emissions so that the increase in global mean temperature can be limited to 2 ° C; In the high emission scenario (1142 ppm CO2 in 2100) it is assumed that there are no efforts to reduce greenhouse gas emissions, so that the increase in global mean temperature according to the available calculations is around 5 ° C.

Notes for editors:

Your scientific contact at the Alfred Wegener Institute is Dr. Tido Semmler, Tel. 0471 4831-2287 (E-Mail: Tido.Semmler (at)

Your contact person in the AWI press office is Dr. Folke Mehrtens, Tel. 0471-4831-2007 (E-Mail: medien (at)

The Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) conducts research in the Arctic, Antarctic and the oceans of temperate and high latitudes. It coordinates polar research in Germany and provides important infrastructure such as the research icebreaker Polarstern and stations in the Arctic and Antarctic for international science. The Alfred Wegener Institute is one of the 19 research centers of the Helmholtz Association, the largest scientific organization in Germany.

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Features of this press release:
Biology, chemistry, geosciences, ocean / climate, physics / astronomy
Research / knowledge transfer, research projects