Climate change and uncertainty: consequences for policy making on adaptive responses

1. www.bjerknes.uib.no Climate change and uncertainty: consequences for policy making on adaptive responses Helge Drangehelge.drange@gfi.uib.no

2. Some observations Temperature Precipitation Sea level

4. 2008

5. 2009

6. 2010

7. 2011

8. 1911

9. Distribution of observed summer temperature 1960-2011 (1σ ~ 1/3; 2σ ~ 1/20; 3σ ~ 1/400; 4σ ~ 1/16000) 1/16.000 1/400 Hansen et al. (2012)

10. Precipitation: Air's water vapour holding capacity increases with increasing temperature (Clausius-Clapeyrons expression) 90 80 70 60 50 40 20 20 10 • Regions with high humidity get wetter  Incr´d precip • Regions with low humidity get incr problems forming clouds  Reduced precip 5-7 % increase pr °C increase Relative humidity in air (%) -30-20-10010203040 Temperature (°C)

11. Observed mean change in precipitation, 1951-2010 Winter (mm/decade) Wetter Dryer van den Besselaar et al (2012)

12. Observed mean change in precipitation, 1951-2010 Summer (mm/decade) Dryer summers (but incr’d extreme precip) van den Besselaar et al (2012)

13. Global sea level from tide gauges and satellite (1870 - 2011) Present increase of ~3 mm pr year Change in sea level (cm) Church & White (2006) + AVISO

14. Summary: Earth´s climate is changing. Mainly caused by human emissions of greenhouse gasses.

15. What we are heading at uncertainty ≠ no certainty

16. Change in global temperature, 15 models (relative to 1961-1990)

17. Change in global temperature, 15 models (relative to 1961-1990) +2 °C 2035-2075 For a global, mean warming of ~2 degrees C, which we may experience around 2050, Earth's climate will be comparable to the climate ~3.2 mill years ago Global emission top in 2040, 650 ppm CO2-eq in 2100

18. On local scale Much harder to do local than continental/global climate projections Random fluctuations in climate is particularly important on local scale and is, unfortunately, essentially unpredictable [May therefore experience periods without (apparent) climate change] Fine-scale climate projections can be made, but added value beyond the visible aspect (“looking nice”) can and should be questioned Harder to make projections of precipitation than temperature; very hard to make projections about local changes in extremes

24. Western Norway, 14 September 2005

26. 14 Sep 2005

27. Changes in observation-based precipitation intensity vs global warming +100 Intensity category (bins of 10%) Shiu et al (2012)

28. Changes in observation-based precipitation intensity vs global warming +100 0 to -20 Intensity category (bins of 10%) Shiu et al (2012)

29. Changes in modelled precipitation intensity vs global warming +10 Intensity category (bins of 10%) Shiu et al (2012)

30. Uncertainty in global and regional temperature projections Hawkins and Sutton (2009) Global scale Internal unc Emsission uncertainty Model uncertainty

31. Uncertainty in global and regional temperature projections Hawkins and Sutton (2009) Global scale Great Britain Internal unc Emsission uncertainty Model uncertainty

32. Uncertainty in global and regional temperature projections Hawkins and Sutton (2009) Global scale Great Britain Internal unc Emsission uncertainty Model uncertainty Far future: Uncertainty from emissions & models Near future: Random variations very important

33. Warming of the ocean May contribute 20 cm in this century Total: 50-100 cm in 2100 +1 (?) m in 2200 Glaciers melting May contribute 15-20 cm in this century Greenland and Antarctica May contribute 10-50+ cm in this century (large uncertainties)

34. Relative sea level rise caused by melting of land ice Factor 0.4-0.6 Riva et al. (2010)

35. Summary – We are approaching a climate never experienced by modern man – It is misleading to provide and use one number for a future change in one climate variable – It can be very misleading to use input from one model run to characterise future climate – Ideally, several models, scenarios and approaches should be used to get best estimate and likely range of changes in future climate – Continuous communication and interaction between climate scientists and “end-users” are highly recommended, and possibly the single most important aspect regarding the handling of uncertainty

36. Observed wind

37. Observed wind speed trend, 1979-2008 (m/s per decade) Vautard et al. (2010)

38. Observed storm activity over the British Isles, North Sea and Nordic Sea Long-term decline, large variability, very hard (impossible) to predict variations on time scales shorter than ~30 years KNMI, suppl. (2009) and IPCC (2007)