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solar radiation, like the greenhouse gas increase, is expected to cause global warming. In the stratosphere, however, the two effects produce temperature changes of opposite sign. A monitoring program that would augment long term observations of tropospheric parameters with similar observations of stratospheric parameters could separate these diverse climate perturbations and perhaps isolate a greenhouse footprint of climate change. Monitoring global change in the troposphere is a key element of all facets of the United States Global Change Research Program (USGCRP), not just of the study of solar influences on global change. The need for monitoring the stratosphere is also important for global change research in its own right because of the stratospheric ozone layer.

There are no firm plans at present to implement the primary recommendation of this report, a program of continuous monitoring of solar irradiance to provide the data needed to diagnose and interpret solar influences on climate change. Because current solar radiometric techniques are insufficiently accurate, ensuring data continuity over many decades will require a series of space based observations with sufficient temporal overlap for calibration transfer and prevention of data loss from instrument failure. This measurement program may well be precluded by the dearth of access to space.

Scientific Conclusions

Q: Do solar variations directly force global surface temperature?

A: Yes.

Inexorable change is predicted for the biosphere, that sphere of the terrestrial global environment where life exists. It is imperative to reliably detect, understand, and predict climate change arising from increasing greenhouse gases and aerosols in the Earth's atmosphere. This requires that natural climate forcing, particularly solar variability, also be detected and understood. In the study of solar influences on global change, determining the extent to which solar influences modify global surface temperature is a matter of the highest priority.

Energy from the Sun sustains life on Earth. By far the dominant energy input is the visible solar radiation that heats the Earth's land



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