4. What are climate models used for today? What kind of knowledge do we get with their help?

In the last few years, climate models have become particularly known in connection with the discussion about the greenhouse effect. Climate models are used, for example, to assess how much the earth is heating up or how high the sea level will rise. Also the realisation that the Earth surface on average will warm by 2 to 4 degrees Celsius if carbon dioxide concentrations double is a result of climate simulations. However, global average values are not sufficient to assess the impact of climate change on everyday life. It is much more important to know how climate change could have a particular impact on individual countries or regions. Therefore, regional climate models have been developed in recent years.

The grids of these regional climate models are much finer than the ones used for global climate models: The edge length of a grid box is only a few kilometres instead of about 100 kilometres, allowing to represent local details of climate. In the German Harz Mountains, for example, it rains on the western side whereas just 30 km away on the eastern side it is rather dry. Regional climate models are extensively used. Insurers can assess whether heavy rainfall and flooding will increase in a region. Municipalities can determine how large the sewers under new roads need to be. For the agricultural industry, it is possible to assess whether droughts are more likely to occur in the future - and whether to cultivate plants which can cope with dryness.

Climate simulations are also essential for coastal protection. Barrages and dykes are expensive. In addition, the structures are set to last several decades. Therefore, one must already be able to estimate today how much the sea level will rise or whether the strength of hurricanes will increase. Climate models are also important in order to better understand natural climate changes. Today we know that there are numerous natural climatic cycles. Apart from the oscillation between warm (interglacial) and cold (glacial) periods, which extend over thousands of years, there are also significantly shorter cycles, such as the climatic phenomenon El Niño. This leads to a change of the ocean currents off the Pacific coast of South America about every four to seven years.

A surprising climate phenomenon has been discussed in recent years: Between 1997 and 2012, the global average temperature barely increased over 15 years, although mankind was constantly emitting more greenhouse gases. Many climate critics, who doubt the greenhouse effect, felt confirmed by this. By using climate simulations, however, experts were able to show that there were already 15-year periods in the preindustrial period, in which the global average temperature had declined as strongly. According to an AWI simulation, this phenomenon occurs approximately 12 times in 1000 years. It is thus conceivable that such a natural variation compensated for the greenhouse effect between 1997 and 2012. In many other cases climate models help to identify and explain natural phenomena.