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.

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