Feedback processes – Key gaps in our understanding of the Arctic climate Tore Furevik Geophysical Institute, University of Bergen Bjerknes Centre for Climate Research, Bergen, Norway Arctic Forum, Washington DC, 25-26 May 2006

Take home message Feedback processes play a key role in the Arctic climate system To reduce uncertainties in climate predictions to a level useful for decision makers: international collaboration and coordination increased understanding of feedback processes improved model formulations

Feedbacks in the climate system Climate perturbation amplified  positive feedback reduced  negative feedback Amplified or reduced Response Radiative (local) feedback Albedo, water vapour, clouds, … Dynamical feedbacks Storm tracks, Ocean circulation, … Biogeochemical feedbacks Photosynthesis (CO2 uptake – blue Arctic?), … Production of sulphurous gases and aerosols, …

The Albedo Feedback Even higher atmospheric temperatures! High atmospheric temperatures Higher ocean temperatures, more heat to atmosphere Even higher atmospheric temperatures! More ice melting More solar energy into the ocean More open water, less albedo

Dynamical feedbacks Nordic Seas 10-15°C warmer than average Caused by atmospheric lows and ocean circulation Dependency on heat import  sensitive to climate changes How will the heat transports change in the future ? °C (Drange et al., Furevik and Nilsen, AGU monograph, 2005)

Uncertainties in climate predictions With weak anthropogenic forcing, natural variability can dominate the climate over several decades Temperature trend (+ 30% CO2 ) Year 1-25 Temperature trend (ºC/decade) South Pole – Equator – North Pole Year 1-80 Temperature trend (+ 120% CO2) With strong anthropogenic forcing, global warming will dominate Less variability when sea-ice has melted (weak albedo feedback) Sorteberg et al, GRL, 2005

Arctic sea-ice Sea-ice extent September 1978-2005 Simulated Sea-ice extent Difference (%) from 1979-1990 mean Satellite observations (1979-2005) Mean change for all IPCC models Change in Bergen Climate Model Spread of the most likely scenarios Spread of all IPCC models Bjerknes Centre NSIDC Here we show the multi-model mean of the models using the B2 scenario. In colour we see the temperature, thin blue lines show the multi-model range (the spread of the model results), and the thicker green lines show the signal-to-noise ratio, which is the multi-model mean change divided by the standard deviation. Note that there is only a modest warming over the oceans, while the continents are getting warmer. There is a clear tendency for larger warming towards north. The north-Atlantic is getting less warm than the Pacific at the same latitudes. The multi-model spread is largest in the north. The signal-to-noise ratio is evidently lowest in the marginal ice zone, where natural variability is large. The recent sea-ice retreat is larger than in any of the (19) IPCC models Due to natural variability or unresolved feedback processes ?

Conclusion Feedbacks are key processes in the climate system Amplify or reduce perturbations Poor understanding hinder reliable climate projections Unknown/unresolved feedbacks can prevent early detection of climate surprises Need for increased understanding To reduce uncertainties to a level useful for decision makers: Large-scale synoptic studies of key processes (i.e. Sheba 1997-1998, SEARCH, IPY, …) Improved model formulation (i.e. AOMIP, CMIP, …) Pan-Arctic coordination and international funding sources to secure collaboration (International Arctic Science Foundation?) Thank you !