The North Atlantic Treaty Organization (NATO) established the "Committee on the Challenges of Modern Society" (CCMS) at the November 1969 meeting of the North Atlantic Council. The CCMS was charged with developing meaningful environmen tal and social programs that complement other international pro grams, and with showing leadership, first, in solution of exist ing problems and, second, in development of long-range goals for environmental protection in the NATO sphere of influence and in other countries as well. A first Pilot Study on Air Pollution was initiated by the CCMS at its inaugural meeting in December 1969. It resulted in documents about the definition of criteria for the effects of air pollutants as well as the development of assess ment methods for air quality in urban areas. A second Air Pollution Pilot Study (1975-1979) worked out the basics for setting up assessment methods for emissions inven tories, techniques for the practical application of meteorologi cal diffusion models as well as the development of guidelines for an Air Quality Management System (AQMS). Within this second Air Pollution Pilot Study attention to modelling concentrated on the Gaussian Plume Model. A third Pilot Study on Air Pollution Control Strategies and Impact Modelling then was initiated in 1979 and started in 1980."

Rapidly increasing concentrations of greenhouse gases in the atmosphere, emerging evidence of global warming and the threat of uncontrollable climate feedback mechan:i,sms are now triggering international action to reduce the emissions of greenhouse gases. In 1989 the Intergovernmental Panel on Climate Change (IPCC), established by the United Nations Environment Pro gramme and the World Meteorological Organization, started preparations for an international convention on climate. This convention is to be followed by protocols (agreements) on the reduction of the emissions of greenhouse gases and other measures and implementation mechanisms to preserve the global climate. After the CFC's, CO is the next in line, as the sources 2 and abatement measures for CH and N 0 are as yet insuffi 4 2 ciently understood. However, the abatement of CO . is a far 2 reaching issue. It will require major changes wi thin the most important sectors of the economy: energy (production and use) and agriculture (deforestations and land use pat terns). Given this situation it is not so surprising that national governments are hesitant to take action. One reason is the remaining uncertainty regarding the rat,e and the extent of climate change. However, further analysis will show that the uncertainties will be outweighed by the increasing risks when measures to reduce the emission of greenhouse gases are delayed.