An international team of specialists has concluded from eight indexes of climate that there is no end in sight to the cooling trend of the last 30 years, at least in the Northern Hemisphere.
In some, but not all cases, the data extend through last winter. They include sea surface temperatures in the northcentral Pacific and north Atlantic, air temperatures at the surface and at various elevations as well as the extent of snow and ice cover at different seasons.
In almost all cases it has been found that the year‐to‐year variations in climate are far more marked than the long‐term trend. The long‐term trend often becomes evident only when data from a number of years are displayed.
The report, prepared by German, Japanese and American specialists, appears in the Dec. 15 issue of Nature, the British journal. The findings indicate that from 1950 to 1975 the cooling, per decade, of most climate indexes in the Northern Hemisphere was from 0.1 to 0.2 degrees Celsius, roughly 0.2 to 0.4 degrees Fahrenheit.
Data from the Southern Hemisphere, particularly south of latitude 30 south, are so meager that reliable conclusions are not possible, the report says. The 30th parallel of south latitude passes through South Africa, Chile and southern Australia. The cooling trend seems to‐extend at least part way into the Southern Hemisphere but there have been indications of warming at high southern latitudes.
The various indexes were reported as follows:
¶ Average surface air temperatures recorded at 358 stations north of latitude 20 degrees south from 1951 to 1975 have been analyzed by Drs. R. Yamamoto and T. Iwashima of Kyoto University in Japan on regional and season bases. A general cooling is evident with “an intensive cooling episode” from 1961 to 1964.
¶ Generally similar trends are evident in temperatures of the lower 18,000 feet of the atmosphere as charted by Dr. Horst Dronia of the Weather Office in Hannover, West Germany. For the period from 1949 to 1976, he has calculated, for 220 points in the Northern Hemisphere, the average temperature of the atmosphere from the separation between the pressure levels near the surface (at 1,000 millibars) and one high up (at 500 millibars). An increase in separation indicated expansion and hence warming. A decrease, for example, of 20 meters (66 feet) was taken to mean atmospheric shrinking, indicating a cooling in that case of I degree Celsius (almost 2 degrees Fahrenheit).
¶ Observations extending higher into the atmosphere confirmed the trend. The authors were Drs. J. K. Angell and. 1. Korshover of the National Oceanic and Atmospheric Administration Laboratories. in Silver Spring, Md.
¶ North Pacific water temperatures compiled by the same agency’s Marine Fisheries Service have been analyzed by Dr. Jerome Namias of the Scripps Institution of Oceanography at La Jolla, Calif. The original source was temperature readings of cooling water intake made by ships at a rate of more than 20,000 a month. The data, plotted for 153 locations, show a gradual cooling broken by a sharp warming in 1967‐68.
¶ A similar study based on data from weather ships in the North Atlantic has been done by Dr. Martin Rodewald, former head of the Oceanic Division of the German Weather Service. Since the seven American weather ships were withdrawn in 1973 only two have remained, but observations of a cooling trend have continued.
¶ A gradual increase in area of the northern circumpolar vortex, the massive flow of frigid air around the Arctic, has been recorded by Drs. Angell and Korshover. In 1976 its southern’ extent was the greatest in 10 years and last winter it was 1 percent larger than in any previous winter observed.
¶ Snow and ice cover in the Northern Hemisphere have varied greatly but there has been a net increase according to a satellite photograph analysis by Dr George J. Kukla of Columbia University’s Lamont‐Doherty Geological Observatory. This has been most marked in the spring when so highly reflective a cover returns much solar energy into space at a time of intense solar radiation.
¶ Antarctic sea ice coverage, after increasing to 1972, has been shrinking.
The observations come, at a time when a warming trend could have been expected from the increase of carbon dioxide in the atmosphere due to extensive fuel burning. The gas inhibits the escape of solar heat from the earth. Dr. Kukla, in a telephone interview this week, said that the cause of the apparent cooling remained unknown and that no scientific attempt to predict whether the trend would continue was possible. Monitoring of the various indexes is continuing, he added.
Source: Associated Press (The New York Times)