The mechanism for global warming is that radiation from the sun passes through the atmosphere, warms the Earth and is reflected back into space. Natural greenhouse gases in the atmosphere, mainly carbon dioxide (CO2) and water vapour, trap some of this outgoing radiation, which subsequently warms the planet. Increasing emissions from burning fossil fuels and changes in land use patterns have, however, led to a significant increase and build-up of greenhouse gases in the atmosphere. Evidence suggests, and experts believe that the Earth's average temperature has already and therefore will continue to rise in line with increasing levels of greenhouse gases, and that global climatic changes in the form of shifts in temperature and rainfall could move climatic zones towards the poles, accelerating sea-level rise, modifying ocean circulation and ecosystems.
A key factor in assessing the consequences of climate change is the inertia of the climate system: climate change occurs slowly and once a significant change has occurred it will not disappear quickly. Hence, even if a stabilization of greenhouse gas concentrations is achieved, warming could continue for several decades, and sea levels could continue to rise for centuries.
Agenda 21 indicates that analysis of data for indication of climate change as a basis for developing remedial measures is a complex task. Extensive research is necessary in this area and due account has to be taken of the work of the Intergovernmental Panel on Climate Change (IPCC), the World Climate Programme, the International Geosphere-Biosphere Programme (IGBP) and other relevant international programmes.
The World Meteorological Organization and UNEP established the Intergovernmental Panel on Climate Change (IPCC) in 1988 to assess current scientific knowledge on the enhanced greenhouse effect, global warming and climate change. The panel published its initial findings in 1990, and confirmed that atmospheric greenhouse gas concentrations were rising and could affect global temperature and climate. In May 1991, the 16th UNEP Governing Council agreed to help governments, particularly those of developing countries and small island countries, carry out national studies on the costs and benefits of dealing with predicted climate change. Improvements in computing capabilities will allow more refined simulations of the path of climate change and better understand key processes. Improvements in climatic date collection and analysis are also expected.
In assessing the possible impact of rising atmospheric concentrations of CO2 and other greenhouse gases (GHGs), the WMO/UNEP Intergovernmental Panel on Climate Change (IPCC) concluded in its 1995 report that 'the balance of evidence suggests that there is a discernible human influence on global climate' (IPCC 1996a). Recent research suggests that climate change would have complex impacts on the global environment. The IPCC mid-range scenario projects an increase in global mean temperature of 2.0 degrees, within a range of 1.0 to 3.5 degrees (C), by the year 2100, the largest warming in the past 10 000 years. Average sea level is projected to rise by about 50 cm, within a range of 15 to 95 cm, by the year 2100. A 50-cm rise in sea level would lead to the displacement of millions of people in low-lying delta areas and a number of small island states could be wiped out (IPCC 1996b).
A US$35 million international experiment using underwater sound to investigate the reality of global warming, known as Acoustic Thermometry of Ocean Climate (ATOC), was scheduled to begin in 1995. From a depth of about 900 metres, speakers off California and Hawaii were to rumble intermittently with low-frequency noises. Thousands of kilometres away, underwater microphones all over the Pacific were to pick up the faint signals. Since sound travels faster in warm water than cold, changes in the sound's speed as it crossed the Pacific could reveal temperature shifts as subtle as a few thousandths of a degree. Such work would try to verify whether computerized global climate models used to predict global warming are accurate or need to be improved.