Man's Impact on the Global Environment.

WHEN fossil fuel is burned, both carbon dioxide and sulphur dioxide are added to the atmosphere The former should cause warming of the lower atmosphere by enhancing the greenhouse effect, whereas the latter, by producing sulphate aerosols, may cause a cooling effect The possibility that these two processes could offset each other was suggested many years ago (see, for example, ref 1), but during most of the intervening period, attention has focused on the greenhouse effect Interest in tropospheric aerosols has, however, recently been rekindled by the realization that they may influence climate, not only through clear-sky radiative effects2–5, but also by modifying cloud albedo6–8 Here I examine the sensitivity of the climate system to simultaneous changes in SO2 and CO2 emissions, as might occur if controls were imposed on fossil-fuel use Over the next 10–30 years, it is conceivable that the increased radiative forcing due to SO2 concentration changes could more than offset reductions in radiative forcing due to reduced CO2 emissions

Could reducing fossil fuel emissions cause global warming

The annual cycles of sea level and surface pressures and the atmospheric pressure owing to water vapor have been analyzed in detail. Global sea level pressures undergo an annual cycle of 0.5 mbar range with a maximum in the northern winter. Global surface pressures, which represent the total mass of the atmosphere, also undergo an annual cycle of 0.5 mbar range but with the maximum in the southern winter. The changes in water vapor concentrations are responsible for the latter—water vapor has a maximum in the southern winter. The constancy of the mass of dry air is used as a check on the accuracy of computations. The total mass of the atmosphere is 513.7 × 1016 kg with a standard error of 0.02 × 1016 kg and an annual cycle of amplitude 0.1 × 1016 kg. The corresponding global mean surface pressure of the atmosphere is 984.68 mbar. The mean total mass of water vapor is 1.3 × 1016 kg which corresponds to 2.53 cm of precipitable water or 12906 km3 of water at 0°C. The distribution of pressure and mass as a function of latitude are also presented. A substantial annual exchange of mass occurs between the hemispheres amounting to 0.7 × 1016 kg of dry air (2.7 mbar range in hemispheric averaged pressure). Maximum pressures occur in winter, and the summer loss of mass is partially compensated for by increased water vapor amounts. The maximum net meridional flow occurs across 5°N in the transition seasons. In the northern hemisphere, water vapor undergoes an annual cycle with a range of 1.5 mbar (area averaged) and a summer maximum, and the sea level pressure owing to dry air undergoes an annual cycle of range 5 mbar and a winter maximum. Of this, 54% is due to exchanges with the southern hemisphere and 46% is due to changes in the artificial atmospheric mass used to correct from the surface to sea level.

Seasonal variations in global sea level pressure and the total mass of the atmosphere

The occurrence of lead in Antarctic recent snow, firn deposited over the last two centuries and prehistoric ice

THE results of the variations of the concentrations of 12 elements including Pb, Cd, Cu, Zn and Ag in snow deposited from 1914 to 1974 at an uncontaminated site in East Antarctica are discussed here. As the composition of snow in central Antarctica is shown to be closely correlated to that in the lower atmosphere, this provides us with a valuable historical record of the composition of remote aerosols in the Southern Hemisphere. We find that Pb, Cd, Cu, Zn and Ag were already strongly enriched 60 yr ago (with respect to the composition of reference crustal and marine sources), and that both the concentrations and the enrichment factors observed in 1914 for these five elements are comparable to the present ones. This suggests that the present background atmospheric concentrations of Pb, Cd, Cu, Zn and Ag in the Southern Hemisphere are not strongly influenced by global pollution, but are related to natural phenomena, possibly volcanism.

Trace metals in Antarctic snows since 1914

Two globally extensive forms of atmospheric pollution (carbon dioxide and particulate loading) are each considered from the viewpoint of long-term changes in their total abundance, and the impact of such changes on the equilibrium temperature of the Earth.

J. Murray MitchellJr.

Papers

A Reassessment of Atmospheric Pollution as a Cause of Long-Term Changes of Global Temperature