State of the Arctic
While the planet has warmed by 1°C since the late 19th century, the warming in the Arctic has been 2–3°C. This session addresses the current observational basis and causal understanding of the observed change manifested to date in Arctic Atmosphere-Ocean-Cryosphere interactions, and impacts on ecosystems – marine and terrestrial. We foresee a session benefitting from recent and ongoing efforts in documenting and understanding the state of and change in the Arctic such as the 2017 SWIPA report and the IPCC’s Special Report on Global Warming of 1.5°C (SR1.5) and Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC).
We welcome abstracts addressing one or more of the topics further specified below, including state estimates and quantifications of causal links and processes. Both observation-and model-based studies are welcome; we particularly appreciate studies integrating both approaches.
One of the largest manifestations of Arctic change is the rapid shrinking and thinning of the Arctic sea ice cover and the consequences thereof. Feedbacks from sea ice loss has played a significant role in Arctic warming, but other factors such as increased down-welling longwave radiation from increased cloud cover, atmospheric moisture from local and remote sources and greenhouse gases, as well as changes in oceanic and atmospheric circulation are also important. Atmospheric responses to sea ice loss depend in part on the state of the background atmospheric circulation pattern with some sea ice reduction years having a smaller influence on tropospheric warming than others.
Also, mass loss of the Greenland Ice Sheet and of glaciers surrounding the Arctic has likely become the dominant source of sea-level rise in recent years. The importance of ice-ocean interaction for this mass loss, both at the interface of marine-terminating glaciers, but also through increased runoff from land-terminated glaciers, illustrates the importance of understanding the coupling of Arctic climate dynamics for the entire planet.
Permafrost is the third mayor component of the Arctic cryosphere. Extensive warming or thaw of permafrost has persisted for decades and is expected to accelerate. This in turn affects greenhouse gas dynamics, as previously frozen organic matter in soils and sediments is exposed to decomposition. Permafrost thaw causes a feedback to global warming that is comparable to climate forcing from all human land-use. These processes occur over vast areas, but are characterized by a high degree of spatial and temporal variability, which makes accurate scaling or projections challenging.
The oceans of the Arctic are changing more rapidly than the global ocean as a whole with pronounced changes on a decadal timescale in temperatures, stratification, freshwater content, ice cover and pH. With the retreating sea ice, Atlantic and Pacific water masses reach further poleward; there is increasing evidence that the oceanic influx is causal in the former, particularly for wintertime sea ice change. Adding to this is the prominent interannual to multidecadal variability in hydrography, suggesting that the ocean is key to disentangling natural and forced change in Arctic climate, including maritime continental climate and near-term predictability. In the Arctic shelf-seas, there is evidence that sub-sea permafrost is rapidly thawing, which in turn may affect greenhouse-gas release.
The Arctic Oceans are also very important carbon sinks since despite constituting only ~4% of the total ocean surface area they account for ~12% of the ocean’s total annual CO2 uptake. Further, since the cold waters of the Arctic have weak buffer capacity this means that ocean acidification is more severe than elsewhere.
Changes in the physical conditions of the Arctic seas are affecting marine and terrestrial species and ecosystems, from primary production to top level predators. The impacts are geographically diverse, but with some general patterns. The ongoing temperature rise and reduced ice cover are already altering ecosystem function and geographical distribution of important species. In the sea this is e.g. pronounced in the north – and eastwards habitat expansion of key boreal fish stocks in the Barents Sea and Atlantic mackerel now being present off Greenland. The retreat of sea ice has also led to an increase in primary production and increased incidence of fall blooms. Eventual loss of the summer ice cover will have profound consequences for life in the Arctic seas. Furthermore, plankton species that form calcium carbonate shells or exoskeletons are highly vulnerable to ocean acidification and associated changes in mineral saturation states. Very often such species form the bottom of the food web, and the overall effects of ocean acidification on ocean ecosystems is still largely unknown.
On land, climate and environmental changes are profoundly affecting Arctic ecosystems. While some species may persist through adapting their geographical ranges, other species are less resilient. In many areas forests are migrating poleward and there is evidence of extensive shrub-expansion in tundra ecosystems. Permafrost thaw is also causing rapid changes to landforms and landscapes, altering important habitats and nesting grounds.
Scientific committee members:
- Ben Marzeion, University of Bremen, Germany (co-lead)
- Geir Ottersen, Institute of Marine Research, Norway (co-lead)
- Julienne Stroeve, University College London, NSIDC, United Kingdom (co-lead)
- Gustaf Hugelius, Stockholm University, Sweden
- Siv Lauvset, Uni Research Climate, Bjerknes Centre for Climate Research, Norway
- Tor Eldevik, University of Bergen and Bjerknes Centre for Climate Research, Norway
Alexey Pavlov email +47 948 45 342