1. 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, May 2006

2. 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

3. 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, …

4. 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

5. 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)

6. 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

7. Arctic sea-ice
Sea-ice extent September
Simulated Sea-ice extent
Difference (%) from mean
Satellite observations ( )
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 ?

8. 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 , 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 !