Arctic haze can affect global climate

How often do we look at the sky each day? Again and again, our gaze moves up to watch the display of passing clouds. Up to now, clouds have been also an unknown component in the calculations of arctic scientists trying to explain the phenomenon of arctic haze. However, scientists of the Alfred Wegener Institute for Polar and Marine Research (AWI) at the Potsdam Research Unit were able to use new data to somewhat 'lift the hazy veil'. The results have now been published in 'Geophysical Research Letters'.

The supposedly 'clean' Arctic is overcast with a layer of haze, particularly in winter and spring. The haze is composed of numerous fine dust and liquid particles, so-called aerosols. Aerosols originating from industrial regions of Europe, Russia and North America are carried to the Arctic. They attract water droplets, and condense into clouds, thus influencing climate. Depending on their composition, the particles either absorb or reflect sunlight, thus changing the amount of radiation reaching the earth’s surface. This changes temperature by a maximum of plus or minus three degrees Celsius. Under the direction of scientists from the AWI and the Japanese National Institute for Polar Research, international expeditions to the Arctic were carried out continually throughout spring for the purpose of precise location measurements at altitude (using aircraft) and at ground level.

Scientists from Potsdam are now feeding their computers with data from the research project ASTAR (Arctic Study of Tropospheric Aeorosol, Clouds and Radiation), as well as with long-term data records from the AWI station in Ny-Ålesund, Spitsbergen. A detailed mathematical arctic model is used for their calculations. In contrast to global climate models, this Arctic-specific model describes the conditions at North Pole regions in a more detailed manner and is, thus, more realistic.

Using this particular climate model, scientists calculated strong regional and seasonal temperature fluctuations within the highly complex and sensitive arctic region. They also discovered, that aerosols not only affect temperature, but also change atmospheric circulation. Usually, there is a clear cycle of cloud formation, rain and new cloud formation. Aerosols, however, can change this cycle, for example, by altering the lifespan and properties of clouds (e.g. droplet size and water content). In moist air, aerosols swell and, therefore, can increasingly absorb or reflect solar radiation. Consequently, the temperature within the aerosol layer rises or falls. This leads to a complete change in the vertical distribution of temperature, which may further alter cloud cover, for instance. Cloud cover, in turn, affects the incoming radiation and, hence, circulation.

In addition, simulations have shown that the presence of aerosols leads to a reduction of air pressure at ground level in the eastern Arctic, because the low pressure system with its centre over Iceland is extending further north. As a result, the North-South-exchange of heat and humidity is altered. This has effects on global climate. Moreover, there is evidence that aerosols have the potential to change natural large-scale oscillation patterns, such as the 'Barents Sea Oscillation', or the 'North Atlantic Oscillation'. The North Atlantic Oscillation is a climate phenomenon characterizing the fluctuations in air pressure between a low-pressure system over Iceland and a high-pressure system over the Azores. With a high-pressure differential, winters in northern Europe turn out to be wet and mild, while a low differential leads to cold and dry winters. Aerosols can intensify these effects. Therefore, the arctic haze layer may also influence the climate in our latitudes.
Bremerhaven, September 14, 2004