1. Colloquium “Searching the climate record for a human signal” 31 aug 2011 Climate scientists must communicate uncertainties and their consequences Bart van den Hurk (Involved in KNMI Climate Change Scenarios)

2. Colloquium “Searching the climate record for a human signal” 31 aug 2011 Climate scientists must communicate uncertainties and their consequences Emphasised by antagonists of anthropogenic greenhouse warming (AGW) theory Emphasised by “alarmists” Originate from natural variability imperfect models & knowledge unknown future developments Originate from physical hazards vulnerability of society perception/political view If there is uncertainty, there is risk

3. Colloquium “Searching the climate record for a human signal” 31 aug 2011 If there is uncertainty, there is risk Average temperature change 2090-2100 relative to 1990 Probability uncertainty 0 Cannot be claimed Defined as (politically) “relevant” by e.g. Dutch Delta Committee risk

4. Colloquium “Searching the climate record for a human signal” 31 aug 2011 Positioning KNMI’06 scenarios Average temperature change 2090-2100 relative to 1990 Probability 0 G G+ WW+  Designed to explore possible future conditions not presented as forecasts  Supporting adaptation of society to extreme conditions relevance of different scenarios varies across applications

5. Colloquium “Searching the climate record for a human signal” 31 aug 2011 Concluding  Uncertainties and risks are connected  Ignoring possibility of AGW or alarmist exaggerating implies strong scientific bias and not in the spirit of KNAW code of conduct  Making future explorations is relevant. Scenarios are useful tools for this