Frederick M. Luther

Detecting the climatic effects of increasing carbon dioxide

This report documents what is known about detecting the CO2-induced changes in climate, and describes the uncertainties and unknowns associated with this monitoring and analysis effort. The various approaches for detecting CO2-induced climate changes are discussed first, followed by a review of applications of these strategies to the various climatic variables that are expected to be changing. Recommendations are presented for research and analysis activities. Separate abstracts have been prepared for the individual papers. (ACR)

EFFECT OF RECEIVER ORIENTATION ON ERYTHEMA DOSE1,2

‐The analysis of solar erythema dose under changing ozone amount, previously confined to the study of horizontal surfaces, is extended to include the effects of receiver orientation. A semi‐empirical model is used to calculate erythema (sunburn) dose for non‐horizontal plane areas under cloudless conditions as a function of latitude, season, and ozone amount. According to the model, in middle and high latitudes, surfaces with inclination angles (α) up to 45° receive at least 80% of the daily erythema dose received by a horizontal surface. Much larger reductions in daily erythema dose occur for α > 45°. which can result in a significant reduction in the latitudinal gradient of erythema dose. The amplification factor for erythema dose (Δdose/ΔO3) varies significantly with latitude, but it is only weakly dependent upon receiver orientation. Additional calculations indicate that the amplification factor may be significantly larger for skin cancer than for erythema.

Effect of Temperature Feedback and Hydrostatic Adjustment in a Stratospheric Model

Abstract Calculated perturbations to stratospheric ozone are generally thought to be reduced when temperature feedback is included in the model. We find that when self-consistent hydrostatic adjustment is included with temperature feedback, there can be significant differences in the computed change in local ozone concentration. We present results in two frames of reference (changes in ozone at constant altitude and changes at constant pressure) to illustrate the importance of the frame of reference. Including hydrostatic adjustment is particularly important for calculations of the change in local ozone at constant altitude due to CFM, CO2 and H2O perturbations because large changes in the temperature structure are predicted. Only small differences are computed for increases in N2O. Air density adjustment in a constant pressure frame of reference is important when local temperature changes are large.

Climate Change Due to Anthropogenic Surface Albedo Modification

Numerical experiments that dealt with the possible climatic impact of man-induced surface albedo change have primarily focused on individual regions (e.g. increased desert albedo, tropical deforestation, urbanization). Sagan et al. (1) suggest that the combination of anthropogenic albedo changes may have contributed to global climate changes in the past and may be continuing today. Using a statistical dynamic climate model with more realistic surface albedo changes than used in previous experiments, we have conducted a numerical experiment combining desertification of the Sahara and deforestation of the tropical rain forest. Over an area of 9 × 106 km2 at 20°N the desert albedo was increased from 0.16 to 0.35 and over 7 × 106 km2 at the equator and 10°S the rain forest albedo was increased from 0.07 to 0.16. While the most significant direct climatic responses were observed in the modified zones, high northern latitudes exhibited the greatest cooling through activation of the ice-albedo feedback process. In contrast to Sagan et al. (1), this experiment suggests that anthropogenic modification of surface albedo over the past few thousand years has had an impact on global climate which is likely quite small and probably undetectable.

Solar Absorption in a Stratosphere Perturbed by NOx Injection.

The changes in the solar absorption by nitrogen dioxide and ozone induced by the injection of NOx (oxides of nitrogen) in the stratosphere are complementary, even though the nitrogen dioxide absorption is only a small fraction of the ozone absorption for an unperturbed stratosphere. The factors causing this effect are described, and an analysis is made of the perturbed solar radiation budget.

Ozone depletion calculations

Models of stratospheric chemistry have been primarily directed toward an understanding of the behavior of stratospheric ozone. Initially this interest reflected the diagnostic role of ozone in the understanding of atmospheric transport processes. More recently, interest in stratospheric ozone has arisen from concern that human activities might affect the amount of stratospheric ozone, thereby affecting the ultraviolet radiation reaching the earth’s surface and perhaps also affecting the climate with various potentially severe consequences for human welfare. This concern has inspired a substantial effort to develop both diagnostic and prognostic models of stratospheric ozone.