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The Arctic Sea ice

The floating sea ice of the Arctic covers an area equal to that of the United States. The permanent presence of sea ice, ice sheets, and continuous permafrost are unique features of the Polar Regions. Even though it is characterized by its harsh environment and vast landscapes the Arctic serves as the home of many forms of life, including organisms living in the ice, fish and marine mammals living in the sea, birds, land animals such as polar bears, and human societies. But much more than that, its white ice cover reflects huge amounts of sunlight and thereby helps the world stay cool.

Today the latest state-of-the-art climate models include as many physical, biological and chemical processes as possible. The models are based on mathematical equations that describe the behaviour of the atmosphere and ocean, and their complex interactions with other components of the Earth system, such as the land surface, the biosphere (animals, plants and microbacterias) and the cryosphere (ice mass, such as glaciers and ice sheets). Their core goal is to describe how certain variables in the coupled atmosphere-ocean system, such as temperature, air pressure, winds or ocean currents, have changed in the past and will most likely change in the future. But the climate system is very complex and understanding or predicting climate changes in the future is a very difficult thing to do. And with weather forecasts becoming inaccurate after just a few days, one can easily ask how we can even claim to project most likely weather conditions in the future?

Low probability, but high impact scenarios: Introducing the backgrounds of a “Dangerous Climate Change”

The balance of scientific evidence now suggests that anthropogenic greenhouse gas emissions are having a significant effect on the earth’s system and especially on the earth’s climate. Since the 1970s, there has been a significant increase of extreme weather events. Tropical and extra-tropical storm frequency and magnitude have considerably increased and so have the flood risks and heatwave occurrences along with very severe socio-economic and ecological impacts all over the globe. Even though the natural science of extreme weather events has progressed over the last decades, modelling climate scenarios still remains pretty speculative. However, it is now scientific consensus that if we continue to follow our “Business as usual”-path and if the greenhouse gas emissions weren’t cut drastically within the next decades, the impacts of a changing climate will intensify throughout the 21st century, with dangerous high impact scenarios becoming more likely to happen. A “dangerous climate change” with raising temperatures especially above 2°C (above pre-industrial levels) could tip certain ecological thresholds and trigger non-linear processes and feedback loops within the earth’s system, forcing the system rapidly into a totally new equilibrium. Dramatic changes within the carbon cycle, the eco- and hydrosphere and most obviously within the kryosphere would exceed our society’s ability to adapt to these changes. Unmanageable and most likely irreversible consequences could put our mankind on the edge of extinction. (1)

An obvious increase of extreme weather events such as heatwaves, floods and tropical storms during the last decades has given raise to worldwide concerns and indicates most likely the potential impacts of a global warming in the future. Besides these temporarily restricted events other impacts which emerge only gradually, such as rising sea levels are at least as serious.

Due to the high concentration of natural and socio-economic values located especially around coastal zones, rising sea levels raise significant concern. More than 1.2 billion people, representing 23 percent of the world’s population live on coastal plains at densities about three times higher than the global mean. (1)