Climate change hasn't gone away!

Dr. Faust, the IPCC today published the contribution "The Physical Science Basis" as part of the Fifth Assessment Report. What are the key findings on the causes of climate change? 

Compared to the last report in 2007, we are now more certain that climate change is substantially caused by human activities. Whereas in 2007, it was assumed that at least half of global warming since 1950 was very probably caused by anthropogenic factors, this connection is now extremely probable. In statistical terms, instead of at least a 90 percent probability, we now talk of at least a 95 percent probability – so the link has become clearer. There are now a large number of new studies on the subject that confirm, for example, that the global mean temperature has risen since 1880 by 0.85° C. What is striking here is that the last three decades, in other words the period since 1981, have been the warmest ever.

Does this mean that scientists agree that anthropogenic emissions of gases affecting climate are accelerating the greenhouse effect?
Yes, all the reliable scientific studies agree that the continuous emission of CO2, methane and nitrogen oxides is causing an increase in temperature in the lower atmosphere. This is the case even when these are offset by other anthropogenic activities that have a cooling effect, such as the emission of sulfate particles from industrial processes.

But there have been repeated reports in the media that climate change has stalled, or even stopped, since the increase in temperature has slowed. Has the IPCC an answer to explain this?
It is true that we have seen a relatively low level of warming since 1998. For example, global mean temperature between 1951 and 2010 increased each decade by 0.12° C on average, but since 1998 by only 0.05° C. However, the report shows that climate change is by no means over, as is sometimes maintained. The emission of climate-changing gases is continuing undiminished. The slowdown in temperature increase is to a large extent the result of natural fluctuations in the climate system. Important factors here include El Niño and La Niña, and an oscillation in sea-surface temperatures in the Pacific that can last for decades. The current cool phase has helped to reduce the warming trend. When viewed from the more short-term perspective of just a decade, natural climate fluctuations can sometimes mask the long-term trend.

Are there any other reasons for this?
Effective solar radiation in the last 15 years was also weaker than in the years before. As the result of several volcanic eruptions and concentrations of industry in Asia, vast quantities of sulfate particles have reached the upper atmosphere, and these produce a cooling effect. In addition, the intensity of solar radiation fluctuates in an 11-year cycle. Following a relative maximum in solar activity in 2000, there was a steady decrease in the level of radiation up to 2009. Since then it has been rising again, but has still not reached the original level of 13 years ago.

So climate change hasn't gone away. What are the implications for society and for insurers?
The report makes it unmistakably clear that in certain regions of the world, we must brace ourselves for more frequent extreme weather events. It confirms that the number of such events has increased and it has specified the regions affected. So, in most regions, we may expect a further increase in intense rainfall, and a greater number of regions will also be affected by heat waves and droughts. In the long term, severe tropical cyclones will occur more frequently in certain ocean basins.

Dr. Faust, you are also working as lead author on a chapter of the Working Group II report (Impacts, adaptation and vulnerability). What topics are you looking at? Within this working group, which is concerned with the impact of climate change and possible adaptation measures, I am jointly responsible for the chapter "Key economic sectors and services". My colleagues and I examine the impact of climate change on the sectors energy, water, transport, farming and forestry, recreation and tourism, and of course, on public finance and insurers in particular. We will be presenting our findings in March 2014.