Anthropogenic climate change, scenarios and acceptance

1. Anthropogenic climate change, scenarios and acceptance Hans von Storch Institute for Coastal Research, GKSS Research Center and KlimaCampus*, Hamburg University, Germany *The German Excellence Center for Climate Science

2. Who is this? Hans von Storch (born 1949) Diploma in mathematics,PhD in meteorology Director of Institute for Coastal Research, GKSS Research Center, near Hamburg, Professor at the Meteorological Institute of Hamburg University Works with social and cultural scientists.

3. Iberian Peninsula

4. Detection and attribution The IPCC’s (TAR) attribution argument

5. Assessment: Is Global Warming real? Climate scientists have been surveyed about their view about climate change. 2/3 are convinced that most of the observed ongoing warming is related to human action Bray, D. and H. von Storch, 2007: Climate Scientists’ Perceptions of Climate Change Science. GKSS-Report 11/2007 We can say for certain that global warming is a process already underway. agree disagree

6. Which weather elements change? Not all. Regional temperature (example: Denmark) consistent with anthropogenic global mean temperature rise, but storms do not change at the same time. Temperature Frequency of storms

7. Damages and extreme weather

8. The increase in damages related to extreme weather conditions is massive – but is it because the weather is getting worse? Losses from Atlantic Hurricanes Hardly “Great Miami”, 1926, Florida, Alamaba – damages of 2005 usage - in 2005 money: 139 b$ Katrina, 2005: 81 b$ Pielke, Jr., R.A., Gratz, J., Landsea, C.W., Collins, D., Saunders, M., and Musulin, R., 2008. Normalized Hurricane Damages in the United States: 1900-2005. Natural Hazards Review

9. 2006 meeting of scientists and re-insurances (Munich Re; Hohenkammer, May 2006) Consensus statement:„1. Climate change is real, and has a significant human component related to greenhouse gases.2. Direct economic losses of global disasters have increased in recent decades with particularly large increases since the 1980s.8. Analyses of long-term records of disaster losses indicate that societal change and economic development are the principal factors responsible for the documented increasing losses to date. Damages and extreme weather

10. Visioning futures Future anthropogenic climate change, or Global Warming is described by scenarios. Alternative scenarios about economic and social developments in the coming 100 years are made; from these assumptions emissions of greenhouse gases are estimated; the climatic effect of these are assessed by running climate models. The resulting knowledge are not predictions, but conditional predictions given certain emissions. If, however, all scenarios point to the same development, then they collectively become predictions – namely that temperatures as well as sea level will rise.

11. IPCC SRES Scenarios

12. IPCC SCRES Scenarios

13. Asessement: Does the IPCC reflect consensus? To what extent do you agree or disagree that the IPCC reports accurately reflect the consensus of thought within the scientific community? The scientific community finds that contemporary scientific knowledge about climate and climate change is well assessed by the IPCC (Intergovernmental Panel on Climate Change). Bray, D. and H. von Storch, 2007 agree disagree

14. The question of consensus • There is indeed broad consensus among scientists on some issues, in particular on • the ongoing emissions of greenhouse gases into the atmosphere cause elevated concentrations in the atmosphere and changes in the statistics of weather (i.e., climate). • reducing the emissions will lead to smaller changes of climate. • stronger climate change will be associated with more severe impacts. • With respect to other issues, such as tipping points, tropical storms, future sea level and the fate of Grønland, there is no consensus.

15. Possible Reponses to Anthropogenic Climate Change • In the interacting environment-and-society system, we have to options for response • trying to avoid man-made changes („mitigation“), • or to adapt to man-made changes („adaptations“). • In principle, mitigation is preferable over adaptation, but complete mitigation seems impossible so that the best strategy is to mitigate as much as affordable and to minimize negative consequences by adaptation. Even if the very ambitious 2o-goal of the EU would be achieved, a significant adaption pressure will emerge – greatly enhanced thinking about options of adaption not only in Europe but in particular in more vulnerable parts of the world are needed. The goal of limited warming in 2100 to 2o relative to preindustrial levels (1850) and to reach stabilization of climate is politically motivated, and most climate scientists consider the chances of success of being remote.

16. Epilog: The service of science The debate about global warming has rightly become a political debate, which unfortunately spills over to science – where scientists act as “stealth advocates” for value-based agendas. In the course of this process, the authority of science is eroding, as it becomes difficult to distinguish between scientific analysis from science and advice from NGOs or other value-driven social actors. In this model, science gets the role of auxiliary troops for broader social movements. To maintain the service provided by science to society – namely to provide “cold” knowledge which may help to sort out some aspects in an otherwise passionate and value-driven decision process – scientists should limit themselves to assessment of robust scientific knowledge and should avoid normative statements beyond their expertise. (They may do that if they act as citizens, of course.) Politicization damages the social institution “science”.