There now seems little doubt that energy planners have to take the carbon dioxide threat seriously. Recent studies show concern over possible climatic warming to be soundly based. They also suggest that even a slight warming -- say less than 1 degree C. -- could be hard on US and Soviet grain lands.
Atmospheric scientists have wondered for some time whether or not increased burning of fossil fuels could load the air with enough heat-trapping CO to raise global average temperature several degrees over the next century. Early this winter, a (US) National Academy of Sciences study group reported it had taken a hard look at the assumptions and uncertainties that underlie this concern and can find no fault with them.
In a study reported about the same time, Syukuro Manabe and Ronald J. Stouffer of the US National Oceanic and Atmospheric Administration simulated CO[ 2] warming with a computer model. This showed that doubling the air's CO, content (which could easily happen over the next 50 to 75 years) could reasonably be expected to bring a 2-degree warming -- a finding typical for such studies.
Meanwhile, Douglas V. Hoyt of the Cooperative Institute for Research in Environmental Sciences in Boulder, Colo., has tried to find out how much CO warming we have already had. Removing what he takes to be sun-related temperature trends from data for the period 1880-1970, he finds a residual warming of around 0.4 degrees that could well be due to CO. It's an uncertain conclusion. Yet Hoyt says it supports estimates that doubling atmospheric CO could warm Earth by 2 to 3 degrees. also, if the present CO[2 ] trend continues, a further 0.4 degree warming over the next 20 years is indicated.
Such small warmings could imply substantial climatic changes. To try to get a feeling for this, T. M. L. Wigley, P. D. Jones, and P. M. Kelly of the Climatic Research Unit at Britain's University of East Anglia have compared the five warmest years with the five coldest during the period 1925- 1974. Reporting their study in Nature in January, they explain it is only a rough guide. Comparing two five year groups is not the same as comparing two climatic epochs. Nevertheless, it does call attention to possible types of change. In particular, a warming of as little as 0.6 degrees implies such striking features as increased rainfall over india and increased dryness for the central and southeastern United States and much of Europe and the Soviet Union. Such changes, the scientists note, "could have considerable impact on agriculture."
These recent studies don't prove that heavily increased use of coal would ruin the climate. But they do emphasize that scientific uncertainties can no longer be an excuse for ignoring this possible limit on coal power in energy planning.