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Workshop 5
“Anthropogenic Climate Destabilization: A Worst-case Scenario”
Participant Statement
September 12–14, 2008 | Bellevue, Washington
Andrey Ganopolski
What are the three critical questions you would ask pertaining to “anthropogenic climate change: a worst-case scenario” – and why?
1. How realistic are current climate models in simulation of non-linear aspects of climate response to global warming?
The current generation of climate models represents a product of relatively long history of numerical climate modeling. They are extensively tuned to empirical climatology and, to some extent, validated against instrumental data for the past century. However, this is primarily related to quasi-linear aspects of climate response to changes in the concentration of greenhouse gases. If the climate system is indeed a strongly non-linear one, as indicated by paleoclimate data, then the ability of climate models to predict such strongly non-linear behavior remains essentially unknown due to difficulties in models validation and large inter-model differences.
2. What is the shortest timescale of the Greenland and Antarctic ice sheets of the response to global warming?
Simulations performed with the ice sheet models indicate that the response time of Greenland, and, especially, Antarctic ice sheet to global warming is rather long, and even for the extreme climate change scenarios it takes several millennia for a complete melting of the ice sheets. This would imply a rather moderate contribution of the ice sheets to global sea-level rise. However, the current generation of ice sheet models does not properly describe a number of important glaciological processes (such as ice streams) that may be important for the response time of the ice sheets.
3. What can we learn from the abrupt climate changes in the past about potential tipping points in the climate system?
There is a growing body of paleoclimate records that indicates that at least several components of climate system (Atlantic thermohaline circulation, ice sheets, shelf ice, etc.) were involved in numerous abrupt climate changes during the glacial age. It is still not possible to realistically simulate any of these abrupt climate changes with the climate models used for future climate change prediction. The important question is whether this fact casts doubts on the reliability of the future climate predictions taking into account that climate instability of the glacial age cannot be considered as a direct analogy for future climate change.
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