Responding to the climate sceptics

Swiss Re argues that the climate is warming at a rate which cannot be explained with natural factors alone.

We have for sometime been vocal that global warming is happening and is mainly caused by man-made activity. So how should we consider the arguments of the climate sceptics?

Although there is plenty of evidence for man-made climate change, there is room for scientific discussions about climate issues because we still do not have sufficient knowledge about all climate processes to be 100% certain about the future development of global warming. While some sceptics can be compared to “flat earthers”, people holding onto outdated and disproved theories, it can be argued that others are healthy challengers to the current state of knowledge in climate change science, even if their views serve specific political and commercial ends as well.

In a field of such complexity, however, the devil is in the detail. The sceptics make a series of claims, often on a general level, which have to be put under scrutiny by the scientific community. Urs Neu at ProClim, in collaboration with our own Natural Catastrophe and Sustainability and Emerging Risk colleagues, Mark Wüest and Martin Weymann, has reviewed scientific evidence on some of the key sceptic arguments in detail – here are the highlights:

• According to present knowledge of physical processes in the climate system there is no known factor other than rising greenhouse gas concentrations which quantitatively explains the observed warming of recent decades.
• All known natural factors influencing climate either act on longer time-scales (eg orbital parameters which cause ice age cycles on tens of thousands of years) or have not changed significantly over the last few decades (solar irradiance, cosmic ray flux, volcanic activity). There is no known natural factor whose recent evolution could explain the recent warming.
• Current climate models are able to reproduce the climate of the past, but can only simulate the recent warming if the effect of anthropogenic greenhouse gases is taken into account. Natural factors alone would lead to a slight global cooling over the last decades.

In short then, the climate is warming at a rate and with specific effects which cannot be explained by purely natural means. Add the effects of man-made emissions based on solid physical knowledge and the explanation is powerful and convincing for the majority of climate scientists as represented by the IPCC.