Plot shows the ozone values measured by instrument aboard ERS-2 Earth-observing satellite on GOME on November 30. The very low ozone values over Northern and Western Europe are visible as dark blue areas. The Antarctic ozone hole is also clearly visible at the bottom of the picture. Photo: ESA

On Tuesday, November 30, the European Space Agency's ERS-2 remote sensing satellite detected abnormally low ozone levels over north western Europe. Above the UK, Belgium, Netherlands and Scandinavia ozone levels were nearly as low as those normally found in the Antarctic. Individual point measurements made from the ground in the Netherlands confirm that local values were almost 2/3 of the normal level at this time of year.

The ozone layer protects our planet from potentially harmful ultraviolet sunlight. A thinning in the ozone layer results in an increase of the amount of ultra-violet radiation. At this time of the year at our latitudes, however, the sun does not rise high enough above the horizon to deliver a significant amount of harmful ultraviolet light.

Mini-ozone holes over Europe are of increasing scientific interest with relevance in the political debate. The previous one was detected in 1997. Tuesday's event is significant not only because of the low levels reached, but also because it was immediately detected by European satellites which are monitoring the entire globe.

Scientists worldwide are studying the exact causes of these ozone lows. They know that these are often associated with exceptionally low temperatures in the lower stratosphere and the presence of polar stratospheric clouds, which contain catalysts which speed up the chemical reactions that destroy ozone. Since the launch of ERS-2 in 1995 Europe is equipped with its own space-borne ozone monitoring instrument, the Global Ozone Monitoring Experiment (GOME).

European expert teams have been using this instrument to produce daily maps of the global ozone layer, and make them available to the public on the world-wide web. This recent ozone low was first drawn to ESA's attention by a team working at the Royal Dutch Meteorological Institute (KNMI) in De Bilt (NL).

Europe is already preparing the next-generation of satellite instruments to improve the monitoring of ozone and other key chemicals in the atmosphere.

ESA's environmental satellite Envisat, designed and built by European scientists and industry, will be launched in 2001 on an Ariane 5 launcher and will carry three new instruments to monitor atmospheric ozone, even more powerful than those carried on board ERS-2.

In addition, ESA and the European Organisation for the Exploitation of Meteorological Satellites, EUMETSAT, are preparing a series of three satellites (Metop) which will carry follow-on GOME instruments and will guarantee at least ten years continued monitoring of ozone from space from 2003 onwards.