The
National Science Board's
Patterns and Perspectives in Environmental Science report of 1972 discussed the cyclical behavior of climate, and the understanding at the time that the planet was entering a phase of cooling after a warm period. "Judging from the record of the past interglacial ages, the present time of high temperatures should be drawing to an end, to be followed by a long period of considerably colder temperatures leading into the next glacial age some 20,000 years from now."
[34] But it also continued; "However, it is possible, or even likely, that human interference has already altered the environment so much that the climatic pattern of the near future will follow a different path."
[34]
The Board's report of 1974,
Science And The Challenges Ahead, continued on this theme. "During the last 20-30 years, world temperature has fallen, irregularly at first but more sharply over the last decade."
[35] Discussion of cyclic
glacial periods does not feature in this report. Instead it is the role of humans that is central to the report's analysis. "The cause of the cooling trend is not known with certainty. But there is increasing concern that man himself may be implicated, not only in the recent cooling trend but also in the warming temperatures over the last century".
[35] The report did not conclude whether carbon dioxide in warming, or agricultural and industrial pollution in cooling, are factors in the recent climatic changes, noting; "Before such questions as these can be resolved, major advances must be made in understanding the chemistry and physics of the atmosphere and
oceans, and in measuring and tracing
particulates through the system."
[36]