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Our present knowledge on the increasing greenhouse effect is based on the 1990 assessment of the Intergovernmental Panel on Climate Change (IPCC) and its 1992 supplement. Model predictions suggest that a doubling of atmospheric CO2 concentration would increase global temperature by 2-4 degrees C. Because time is needed for the upper layers of the oceans to warm up, there is a delay between the realized increase and the estimated equilibrium increase. The 0.5 degrees C increase in global temperature over the past 100 years is in accordance with model predictions but also within the range of natural variability. The IPCC's assessment suggests that if fossil fuel consumption continues according to a 'business as usual' scenario, global temperature will increase at 0.3 degrees C per decade; droughts, flooding and storms would become more frequent and more severe, and sea-level would continue to rise. Analysis of gas in ice cores from Antarctica and Greenland provides estimates of CO2 concentrations in pre-industrial ages; accurate measurement of atmospheric CO2 began in 1958. Atmospheric CO2 concentration has increased from 280 p.p.m. in AD 1800 to 355 p.p.m. at present. Between 1945 and 1973 global emissions of CO2 increased at a rate of 4.4% per year; after 1973 the rate of increase decreased to 1.6% per year. This change permits a test of the CO2 model. Reconstructed CO2 emission agrees within less than 10% with estimated fossil fuel-generated CO2 emission; contributions to CO2 emission from non-fossil fuel sources must be smaller than assumed previously. There are strong indications that in the past changes in atmospheric greenhouse gas concentrations inherent to the glacial-interglacial cycles did play an important climatic role. For example, they were probably responsible for interhemispheric coupling during the major climatic changes. Measures which might stabilize the greenhouse effect include energy conservation and improved energy efficiency, a transition to hydrogen rather than carbon as a source of fuel, and reforestation.

Results from different models for the natural carbon dioxide cycle are compared. Special emphasis is given to the type of ocean modeling (diffusive deepsea or two-box ocean), behavior of the biosphere, and value of the oceanic buffer factor against carbon dixoide uptake. According to the most probable models, the fraction of the cumulative production remaining airborne will be between 46 and 80 percent 100 years from now for any realistic assumptions concerning future carbon dioxide production. For a prescribed maximum increase of 50 percent above the preindustrial carbon dioxide level, the production could grow by about 50 percent until the beginning of the next century, but should then decrease rapidly.

Air entrapped in bubbles of cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. Measurements of the methane concentration in air extracted by two different methods from ice samples from Siple Station in western Antarcitica allow the reconstruction of the history of the increase of the atmospheric methane during the past 200 years.

Aluminum-26 has been detected in a sample of sediment from the South Pacific. The disintegration rate of 0.8 disintegration per minute per kilogram of dry sediment is considerably higher than that expected from cosmic-ray spallation of atmospheric argon; it appears to result mainly from accretion of activity induced in interplanetary dust by solar-flare particles. This finding is in keeping with Wasson's published estimates regarding the magnitude of this effect, and confirms the order-of-magnitude correctness of the solar-particle flux and terrestrial accretion rate of interplanetary dust used in that calculation.