‘Greenhouse’ forecasts seen as premature

Press, 9 April 1988, Page 9

‘Greenhouse’ forecasts seen as premature

The “greenhouse” ; effect will not necessarily bring a general rise! in) sea level, says a University of Canterbury > geographer. Dr Bob Kirk. , j j Dr Kirk will speak at a University of Canterbury seminar today on climate and sea level change with the message that the predictions are uncertain or at best premature, j He feels so strongly about the issue that he declined to take part in | a Ministry for the Environ-ment-sponsored seminar on the subject this week

because it took the presumed i rise as a starting point, i I According to the "greenhouse” theory, the temperature of the atmosphere' will rise because of rising! levels of carbon dioxide land other gases and that will raise sea levels;by ice-cap melting, and thermal expansion of the sea. Dr Kirk, however, said thati the Antarctic was a great deal colder than it I needed to be to maintain glaciation. Furthermbrei if- warmer air were Itq reach Antarctica it wotild be moister, and possibly! result in more precipitation. The result could Ibe growth of the ice cap and a fall in sea levels; he, said.

Dr Kirk did not say that that would definitely occur, but rejected the “simple-minded” assertion that Antarctica would melt. “You can make the opposite argument, equally simple-mindedly,” he said. Dr Kirk, himself experienced in Antarctic research, cited the recent findings of a Wellington researcher, Mr John Sansom, that there was no statistical evidence of warming in Antarctica (“The Press,” April 2). “There isn’t the slightest evidence that it is melting,” said Dr Kirk. On the thermal expansion theory, Dr Kirk said that warmer air would

bring more evaporation, which would mean surface cooling. None of the models of atmospheric warming which he had seen satisfactorily coupled the expansion with the evaporation effects to determine the net result, he sid. There was no consensus among scientists as to the size of the supposed rise. Dr Kirk said that sea levels already differed widely from place to place, because of local factors such as temperature and gravity differences. Satellites had allowed global mapping of the ocean’s surface, showing humps higher than 70m and troughs lower than 100 m from the mean

level. That 180 m gradient occurred across a relatively small distance, from the low point at the Maldives, in the Indian Ocean, to the high point at New Guinea.

The map also showed a 30m gradient between North Cape and Stewart Island. That those "natural” troughs and humps could change over the 50 to 150 years in which the “greenhouse” effect was supposed to occur was “not in doubt,” said Dr Kirk.

Gravity itself could change in localised areas, because of movement of the molten magma under the Earth’s crust. Where sea levels were known to be rising, there was no evidence of a link with the "greenhouse" effect, and there were other areas where sea-level falls of a similar magnitude were being recorded, said Dr Kirk.

The only figures available for New Zealand were provided by tide gauges at Wellington and Auckland. These showed wide fluctuations from year to year, but apparently rising trends since the turn of the century — about 12cm at Auckand and 22cm at Wellington. Dr Kirk said, however, that there was no evidence that those rises were because of “greenhouse” warming. These could be because changes in the "natural” sea contour, falls in the land mass, I or even the wharves sinking on their piles. I New Zealand was “extremely variable”! from! place to place. The West Coast of the South Island, for example, was rising steadily, leaving a series of terraces which were once beaches. '

"The present beach is merely the latest in the series,” he said. j “I am' saying, ‘Listen, let’s" put the brakes on (the discussion of the “greenhouse” effect)’. We have to think about what it means for specific places," he said.

Dr Kirk, whose speciality is coastal geography, said that he had worked on erosion problems for the Timaru; Harbour Board. South Canterbury had suffered widespread erosion for thousands of years, but this had been successfully controlled at Timani since die port was established. ; V i