Impact of Blue Arctic on Climate at High Latitudes

1.The Arctic sea ice is shrinking, both in extent and thickness. In addition to the manmade contribution to the sea ice loss, there are also natural factors contributing to this loss. We have therefore investigated the ice export in 6 climate models from the CMIP5 (Coupled Model Intercomparision Phase 5). Our reults showed that most of these coarse resolution models manage to reproduce a realistic seasonal cycle of Arctic sea ice cover and the ice export through the Fram Strait, with more ice floating through the strait during winter than summer. On the other hand, not all model simulations show an increase in the ice export from the late 1950s and up to today. We interpret that changes in the ice export is not governed by external forcing, such as changes in the CO2 concentration or changes in the incoming sunlight. The ice export is rather controlled by internal climate variability within each model(Langehaug, et al., 2013). 2.The observed Arctic warming during the early 20th century was comparable to present-day warming in terms of magnitude. The causes and mechanisms for the early 20th century Arctic warming are less clear. We for the early 20th century warming analyzed the observed data and the ensemble simulations with the Bergen Climate Model (BCM). Our results indicate that intensified solar radiation and a lull in volcanic activity during the 1920s-1950s led to increased solar radiation over the Arctic region, causing the sea ice to retreat and temperatures to rise. The change in the temperature is closely mirrored by the change in the sea ice(Suo et al. 2013). 3.Observation-based studies suggest that Arctic sea ice change has impact on the atmosphere circulation. We have performed observational analysis and purposely designed coupled atmosphere-ocean (AOGCM) and atmosphere-only (AGCM) model simulations to investigate a new mechanism describing how spring Arctic sea ice impacts the East Asian summer monsoon (EASM). Consistent with previous studies, analysis of observational data from 1979-2009 show that spring Arctic sea ice is significantly linked to the EASM on inter-annual timescales. Our analysis reveal that sea surface temperature (SST) changes in the North Pacific play a mediating role for the inter-seasonal connection between spring Arctic sea ice and the EASM. The mechanism found in the observational data is confirmed by the numerical experiments and can be described as follows: spring Arctic sea ice anomalies cause atmospheric circulation anomalies, which, in turn, cause SST anomalies in the North Pacific. The SST anomalies can persist into summer and then impact the summer monsoon circulation and precipitation over East Asia. The mediating role of SST changes is highlighted by the result that only the AOGCM, but not the AGCM, reproduces the observed sea ice-EASM linkage (Guo, et al., 2014). 4. Early studies showed that the Arctic Oscillation (AO) has impact on the East Asia winter monsoon (EAWM) after 1980s. With combination of the reanlysis products and numercial model simulations, we found that AO-EAWM connection is strengthened after 1980s compared with the period of 1950-1970. The strengthened connection is caused by the reduction in Arctic sea ice (Li et al., 2014). 5. The impact of Arctic sea ice change has been investigated by numerious studies. We have carried out a review on the Arctic sea ice and Eurasia climate (Gao, et al., 2015). It turned out that the remote climate response (e.g., atmosphere circulation, air temperature, precipitation) to the change in Arctic sea ice is hard to be detectable due to internal climate variability. 6. We explore observed atmospheric conditions and feedback mechanisms during summer months of anomalous sea ice melt in the Arctic over 1979-2013. Compared to summer months of anomalous low sea ice melt, high melt months are characterized by anomalous high sea level pressure in the Arctic (up to 7 hPa), with a corresponding tendency of storms to track on a more zonal path. As a result, the Arctic receives less precipitation and less snowfall. This lowers the albedo of the region and reduces the negative feedback the snowfall provides for the sea ice. With the relative anticyclone, 12 W/m^2 more incoming shortwave radiation reaches the surface in the start of the season. The melting sea ice in turn promotes cloud development in the marginal ice zones and enhances downwelling longwave radiation at the surface toward the end of the season. In midlatitudes, the more zonally tracking cyclones give stormier, cloudier, wetter and cooler summers in most of northern Europe and around the Sea of Okhotsk (Knudsen et al., 2015)

The global warming is enhanced in the Arctic where surface air temperature has increased twice as much as the global average in recent decades, also called Arctic amplification. Arctic warming implies melting of sea ice, but its dynamic-thermodynamic resp onse is neither straightforward nor necessarily linear, nor is the response of the atmosphere to sea ice reductions. Satellite observations (1979 to present) show that the Arctic sea ice cover has declined over the past three decades, with a record-low su mmer ice extent in 2007. Furthermore, the projections from the IPCC AR4 models show that the summer Arctic sea ice could disappear by the end of 21st century. Recent studies suggest that the summer Arctic Ocean can be ice-free faster than the projections of the coupled climate models. This will have severe consequences for climate, environment and human activities in high latitudes. Although previous studies show that the variability of atmospheric circulation plays a dominant role in sea ice variability , some observation-based studies also suggest that Arctic sea ice change will have impact on the atmosphere circulation. Numerous simulations (atmosphere-only models, not coupled climate models) have been performed to investigate the potential impact of s ea ice on the atmosphere where sea ice is used as a fixed boundary. The objective of this project is to explore the impact of a summer ice-free Arctic Ocean on the high-latitude climate. The project will consist of comprehensive data analysis and use of t he Bergen Coupled Climate Model and the atmosphere-only model. For the coupled model simulation, a special technique, the so-called partial coupling will be used. The project will compare a Blue Arctic Ocean high latitude climate scenario with the present climate situation in order to quantify and assess the future changes. Improved knowledge about climate change at high latitudes is essential for planning and policy making.