Extreme Weather In The 1970’s
In the 1970s, climatologists blamed the same sort of extreme weather events on global cooling that are now blamed on global warming. And not only the same events, but the same causes.
We are all familiar with the “ice age “scare of the early 1970’s. Science News ran a report at the time, with an interview with C C Wallen, chief of the Special Environmental Applications Division, at the World Meteorological Organisation.
According to the article,
By contrast, (with the Little Ice Age), the weather in the first part of this century has been the warmest and best for world agriculture in over a millenium, and, partly as a result, the world’s population has more than doubled. Since 1940, however, the temperature of the Northern Hemisphere has been steadily falling: Having risen about 1.1 degrees C. between 1885 and 1940, according to one estimation, the temperature has already fallen back some 0.6 degrees, and shows no signs of reversal.
This topic has been thoroughly discussed many times previously, so I don’t intend to rehash the same arguments. I am , though, interested in what climatologists at the time thought about the effects of this cooling.
C C Wallen had this to say,
The principal weather change likely to accompany the cooling trend is increased variability – alternating extremes of temperature and precipitation in any given area – which would almost certainly lower average crop yields.
The cause of this increased variability can best be seen by examining upper atmosphere wind patterns that accompany cooler climate. During warm periods a “zonal circulation” predominates, in which the prevailing westerly winds of the temperate zones are swept over long distances by a few powerful high and low pressure centers. The result is a more evenly distributed pattern of weather, varying relatively little from month to month or season to season.
During cooler climatic periods, however, the high-altitude winds are broken up into irregular cells by weaker and more plentiful pressure centers, causing formation of a “meridional circulation” pattern. These small, weak cells may stagnate over vast areas for many months, bringing unseasonably cold weather on one side and unseasonably warm weather on the other. Droughts and floods become more frequent and may alternate season to season, as they did last year in India. Thus, while the hemisphere as a whole is cooler, individual areas may alternately break temperature and precipitation records at both extremes.
In other words, Wallen observed exactly the same sort of extreme weather then, that is now blamed on global warming – unusual cold, unusual warmth, floods and droughts. And not only the events. The same meridional circulation patterns, that he observed, are happening again now, resulting in cold winters in some places, and warm summers in others.