These are the facts:

• The chemistry of the atmosphere is changing and a global warming is expected due to the increasing concentrations of greenhouse gases and altered amounts of clouds and particles in the atmosphere.

• The stratospheric ozone layer and, consequently, the surface solar flux of ultraviolet radiation, is being modified.

• The oxidation capacity of the atmosphere is changing.

• Trace gases, including those with significant greenhouse warming potential, are abundant.

And, to document and understand these global changes, global cooperation is essential.

The chemical composition of the atmosphere is changing, with far reaching implications for the health of the environment and our future. Carbon dioxide and other greenhouse gas concentrations are increasing. The stratospheric ozone layer is being depleted. There is more tropospheric ozone and higher levels of acidity in precipitation. The radiative balance of the Earth-atmosphere-energy system is changing.

All these reflect the increasing influence of human activity on the global atmosphere. And, the responsibility for the long-term monitoring of global atmospheric composition and its related physical characteristics rests with the World Meteorological Organization (WMO), an intergovernmental organization and a specialized agency of the United Nations, through its Global Atmosphere Watch (GAW), established in 1989, with a coordinated network of observing stations, associated facilities and infrastructure encompassing measurement and related scientific activities. These activities, some of which date back to the 1950s, integrate the efforts of several regional and global networks. WMO facilitates and coordinates the monitoring activities and scientific assessments, and oversees the operation of component networks on a continuing basis, rather than being involved in day-to-day network operations. These are the responsibility of the WMO member countries that operate the stations and provide the central facilities such as quality assurance/science activity centres, world calibration centres and world data centres.

This complex task is being tackled by WMO jointly with other international organizations and the scientific community. In collaboration with the United Nations Development Programme, WMO has recently established through the Global Environment Facility six new GAW stations of global importance at pristine locations in Algeria, Argentina, Brazil, China, Indonesia and Kenya. These fill major climatic and ecological gaps in world station coverage, and join the network of 14 similar stations and over 200 others taking less comprehensive measurements. GAW has also established close cooperation with the International Global Atmospheric Chemistry Programme, a core project of the International Geosphere-Biosphere Programme, and global alliances have been built with other internationally recognized institutes and bodies. The data obtained have already contributed substantially to the scientific evidence which suggests a discernible human influence on global climate.

Assessment of environmental problems, their impacts and the responses to them occupy a prominent position on the international agenda today. By working together, a scientifically effective and economically efficient solution to these problems, confronting all countries of the world, will eventually emerge. Considering this, GAW has matured and is contributing extensively to activities such as the implementation of the relevant parts of the Rio Declaration and its Agenda 21, especially Chapter 9 on "Protection of the Atmosphere". There is increasing recognition by Governments and the global scientific community at large that GAW is an essential tool not only for monitoring the evolution of atmospheric composition but also for improving our understanding of its interactions with all aspects of the environment. In fact, the current knowledge of atmospheric concentrations and trends of increasing emissions of most greenhouse gases are derived from GAW data.

Continuing assessments based on these have kept under review state-of-the-science information on potential impacts of climate change. Mounting levels of greenhouse gases, particularly carbon dioxide, are threatening to change the earth's climate and weather, leading to gradual global warming in the next century. How large this warming and how serious its effects will be will depend on future concentrations of greenhouse gases in the atmosphere. Monitoring greenhouse gas concentrations is therefore of critical importance to evaluate the future of the planet. WMO has been monitoring carbon dioxide levels since the 1960s, when it established a worldwide network that has since become GAW—the major source of information on atmospheric chemistry.

Points of Reference: GAW's monitoring stations

It is, simply put, alarming to state as an example that, at the end of 1996, levels of carbon dioxide in the atmosphere had risen by 29 per cent since industrial times began. And the accumulation continues. In fact, it is proceeding at a rate such that the pre-industrial concentration of carbon dioxide will have doubled by the middle of the next century. The increase can be attributed largely to human activities, mostly fossil fuel use, land use change and agriculture.

The increase of greenhouse gas concentrations leads on average to an additional warming of the atmosphere and the Earth's surface. Many greenhouse gases remain in the atmosphere—and affect climate—for a long time.

The balance of evidence, from changes in global mean surface temperature (an increase of between about 0.3o and 0.6o Celsius since the late nineteenth century) and from changes in geographical, seasonal and the vertical patterns of atmospheric temperature suggest that human activities are causing climate change. The early detection of this change is being made, in large part, through the monitoring efforts of WMO, including the use of data from its Global Atmosphere Watch

It's a wake-up call, warns Topfer; but the ozone layer can still be saved

Following scientific reports that 1998 is shaping up to be the hottest year on record, the United Nations Environment Programme (UNEP) Executive Director, Klaus Topfer, has urged policy makers to take immediate action to limit emissions of carbon dioxide and other greenhouse gases. "Record warming and severe summer heat waves in the United States, India, China and elsewhere are wake-up calls", he said. "We cannot afford to wait several years for the Kyoto Protocol to enter into force before making significant emissions cuts." The Kyoto Protocol is the 1997 agreement under which industrialized countries will cut their greenhouse gas emissions by 5.2 per cent, and will only enter into force after it has been ratified by at least six countries, whose 1990 emissions of greenhouse gases represent over half the total emissions from developed countries. A full recovery of the Earth's protective ozone shield could occur as early as the middle of the next century if the Montreal Protocol on Substances that Deplete the Ozone Layer is fully implemented, say the World Meteorological Organization (WMO) and the UNEP, in their Executive Summary of the Scientific Assessment of Ozone Depletion 1998.

The Global Atmosphere Watch measurements will be essential to the understanding of:

The relationship between changing atmospheric composition and changes of global and regional climate; The impact of changes in climate and other aspects of the Earth system on the chemical composition of the atmosphere; The long-range atmospheric transport and deposition of potentially harmful substances; The natural cycling of chemical elements in the global atmosphere/ ocean/biosphere system, and anthropogenic impacts thereon.