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Anthropogenic climate change, scenarios and acceptance

Hans von StorchInstitute for Coastal Research, GKSS Research Center

and KlimaCampus*, Hamburg University, Germany

*The German Excellence Center for Climate Science

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Detection and attribution

The IPCC’s (TAR) attribution argument

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Assessment: Is Global Warming real?

We can say for certain that global warming is a process already underway.

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 actionBray, D. and H. von Storch, 2007: Climate Scientists’ Perceptions of Climate Change Science. GKSS-Report 11/2007

disagree agree

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Regional temperature (example: Denmark) consistent with anthropogenic global mean temperature rise, but storms do not change at the same time.

Temperature

Frequency of storms

Which weather elements change? Not all.

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Damages and extreme weather

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“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

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

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Damages and extreme weather

• 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.

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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 forecasts, 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.

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IPCC SRES Scenarios

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IPCC SCRES Scenarios

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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

disagree agree

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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.

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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.