Inside the climate model
Climate simulations, climate models - these terms are always used when it comes to global warming. They almost sound like magic sometimes. In reality, however, there is just sophisticated software behind it.
If scientists only had a piece of paper and a pencil at their disposal, they would quickly be at their wits end when trying to calculate the heating of air and water. Atmosphere and oceans, glaciers and sea ice, soil and vegetation - everything plays a role and everything is somehow connected to everything else. Simulation calculations, which are intended to describe what is happening, are of course carried out on the computer.
The software is based on the laws of nature. But the object of their curiosity poses a major problem for climate researchers: the atmosphere and the ocean stretch over tens of thousands of kilometers. Since the equations cannot be calculated for every single point on Earth - which would be neither mathematically nor practically possible - the scientists divide the atmosphere and the sea basins into box-shaped volumes. For each individual box, they calculate how the temperature, the wind or the current speed changes. A dilemma remains: the smaller these boxes are, the more detailed the climate simulations are - but at the same time the computational effort increases to cope with the larger number of boxes.
Despite super-fast computers, climate models are still quite coarse-grained: the atmosphere is divided into boxes that are 200 kilometers long and 200 kilometers wide; the edge length of the ocean is about 100 kilometers. The layers on the sea surface and on the bottom are only 100 meters thick – but the layer thickness increases with increasing altitude in the atmosphere and with increasing depth in the ocean. A climate model today has at least twenty atmospheric and ten oceanic layers.
Which leads to the next problem: Many phenomena - clouds, for example - are so small that they cannot be mapped and imitated with computer programs. However, because these phenomena are important for temperature development, they have to be taken into account in some way. This "somehow" gives whole legions of scientists work: They try to translate small water vortices, the effect of dust particles on cloud formation or the turbulence caused by treetops into mathematical equations for the coarse-resolution climate models.
How well climate models work is ultimately measured by how accurately they reflect reality. For this purpose, the simulated data is compared with climatological measurements. However, reliable meteorological and oceanographic records have only existed for about 150 years - a rather short yardstick.
Many computer models are already doing quite well today - the Indian monsoon, for example, can be simulated just as much as the westerly wind zone in the middle latitudes or the tropical thunderstorm areas. There is still a lack of regional details, but the ever faster computers will increase the accuracy. In addition, experts want to integrate other components of the climate system: air-chemical and biochemical processes, for example. In any case, the scientists cannot yet make real climate predictions – the uncertainties are simply too great. Experts prefer to speak of "scenarios" or "projections" of the climate.
However, part of the uncertainty does not come from the models at all, but from the behavior of mankind: Nobody knows yet how much greenhouse gases will be emitted in the coming decades. After all, a consensus seems to have formed that the global air temperature will rise by around two to four degrees Celsius in the long term if the CO2 content is doubled. Such a warming could mean the complete melting of numerous glaciers and cause the sea level to rise by several meters in the coming centuries - the scenarios agree on this, even with different starting conditions.