new energy: The latest report by the IPCC mentions “exceptions” to an overall trend that is expected to result in even less rainfall in dry regions, and more in wet ones. What does this mean?
Christoph Kottmeier: For Europe, that is a very good description of the situation according to the model projections: more rainfall in Scandinavia, and even less in the Mediterranean. Central Europe is in a transitional area, with somewhat higher winter rainfall expected. Summers could become drier overall, but with intermittent convection rainfall, which could be heavier. In other regions, this basic pattern is less clear.
ne: Why did the report highlight the fact that global warming is predominantly caused by human action? Do any serious scientists still question climate change?
Kottmeier: I think that scientists remain utterly serious when they have doubts, and this field is no exception. And there are serious sceptics. Anthropogenic climate change cannot be demonstrated by means of strictly physical evidence in the same way as the existence of electromagnetic waves or the Earth’s magnetic field. It is more a case of highly compelling circumstantial evidence. However, this evidence, which consists of fundamental considerations in the fields of physics and chemistry, extensive observational data and complex model calculations, is very strong.
ne: There has been no significant increase in the mean global temperature for over 15 years. How do you explain that?
Kottmeier: To date, few attempts have been made at a genuine prediction of mean temperatures for the immediate future; for the most part, statements about future climate change are projections, descriptions of mean future climate patterns over time spans of around 30 to 50 years. It is not unusual for temperatures to stabilise at a high level – or more precisely, to continue to rise slightly – after a sharp increase in the preceding 20 years. Similar phases can be expected in the future, as can longer time spans in which the temperature actually decreases. However, this does not mean the problem is not real, as shown by the alarming loss of Arctic and to some extent Antarctic sea ice.