A NEW LOOK AT CO2

This newsletter customarily brings several items that explain scientific matters in layman's terms, and I strongly suspect that this is the main reason why readers subscribe to it. Nevertheless, this month I would like to include two items whose sources are perfectly accessible to laymen, yet in my opinion so important that I cannot bring myself to relegate them merely to the "Good Reading" column.

Here is a man who evidently knows more about the problem than all the greenhouse alarmists put together; yet he freely admits that the ultimate mechanism of climate change is unknown, though he leaves little doubt that it is far more complicated than the fossil-burning-to-polar-ice-cap-melting contraption pictured by Ehrlich, Lovins and the National Inquirer.

First, Broecker demonstrates that the idea of slow and gradual climate change is mistaken. It is based on the record as obtained from deep-sea sediments, which provide historical clues (for reasons explained in Broecker's essay) to the ice sheet cover in the Northern Hemisphere. The clue that links the two is the abundance of heavy oxygen in the sediment, as shown in the left figure, which plots the heavy-oxygen concentration (and indirectly the ice cap size) over the last 30,000 years. But this indicator is sluggish, smoothes out the quick variations, and tells a misleading story. The more detailed in-dicator, also taken from deep-sea sediments, is the abundance of a certain type of shells, which is directly related to the temperature and follows the changes more quickly (right figure).

[DIAGRAM of deep-sea sediment records]

It will be seen that the two records are compatible, but the one on the right tells a fuller story: climatic changes come about much more abruptly than the left figure would indicate. Moreover, these records tie in with the system that circulates water around the globe, as vapor in the atmosphere one way, and as currents in the deep sea on the return journey. (In the contemporary climate the main cur-rent flows from the Atlantic along Africa into the Southern Indian Ocean, round Australia, and the length of the Pacific to Alaska.)

What causes the "sudden" (as geologists understand the word) flips from one mode to the other? That is the critical question, and the answer lies somewhere in the deep sea salty currents, but is not exactly known.

I lack the arrogance to pass judgment on the quality of Broecker's essay, which lies outside my scientific home ground; what I can safely discern however, is that unlike the stacks of esoteric papers on the greenhouse effect, most of them filled with formulas and hot air, this essay is by a man who has something to say and deserves a hearing.