Are climate models really reliable?

In science, arguing is important and even proper, calling into question man-made models and calculations. Jochem Marotzke, director at the Max Planck Institute for Meteorology in Hamburg, doesn't see it differently. Discussions belong in his area of expertise - and, perhaps, all the more because his research has political consequences. Climate models serve not only aesthetic purposes. They also let heads of state negotiate with each other, make environmentalists take to the roads and cause entire industries to tremble.

"In fact, it is sometimes exhausting that our research findings are exploited for political discussions," said Marotzke to Deutsche Welle. "But that's part of life for a climate researcher - even if the main goal for me and my colleagues is to find out how climate actually works."

Climate models as crystal balls

Marotzke doesn't deal with simple weather forecasts, but with complex climate models. Basic physical laws such as the laws of mass, momentum and energy conservation are mathematically formulated, written down as equations and then calculated with the computer. Climate models provide the scientific results of processes, interactions and regularities of the climate system. They simulate past climate changes, but they also predict future climate conditions.

And it is this glimpse into the future is that has been hotly debated in recent years by meteorologists. Skeptics, who doubt the theory of man-made climate change, repeatedly point to the errors made by climate models when predicting a dramatic increase in global warming.

"As a matter of fact, there is a scientific reason not to blindly trust climate models," Marotzke conceded, "because we can't always prove a model's every assumption."

Increasing discrepancies between climate models and temperature

And, indeed, there was a specific problem that puzzled Marotzke and his British colleague Piers M. Forster.

"We knew that the surface temperature of the earth has been stagnant for 15 years, whereas the models show progressive warming," said Marotzke, referring to the problem.

Were the current climate models therefore wrong? Was there a systematic error in the models? Is global warming just a nightmare? Jochem Marotzke didn't start this research to prove or disprove anything.

"We just wanted to grasp where this discrepancy between models and observations is coming from," explained the meteorologist, when asked about the motivation for his most recent study.

Just a fluke?

The research team has just published his results in the journal Nature. With the help of a multi-step calculation, Marotzke and Forster ruled out systematic errors in the models. Instead, the researchers now blamed serendipity for the current lull in global warming. On the basis of their calculations, they say there is no reason to doubt current forecasts detailing strong global warming.

For laymen this may sound overly simplistic. Are the scientists just blaming chance because they can't find another explanation? Marotzke has no problem with his latest findings.

"As meteorologists, we know that chance and chaos dominate the weather. You have to face the fact that chance plays a big role here."

"It's important that you can clearly distinguish between what happens randomly and what can be explained - which also improves our models," he added.

Marotzke is certain that climate models do not overestimate man-made climate change. In his opinion, this means that global warming will have reached a grave magnitude by the end of this century, if massive climate policy measures are not taken.

In this respect, Marotzke is quite happy after all that his research findings are noted and find their way into public debate.