WHAT'S WRONG WITH OUR WEATHER?

We can now say unequivocally that the warmest period of the present 'interglacial' is over. . . from here on we can expect a cooling off until within about 10,000 years the world will be in the grip of another full ice age." That firm note of conviction runs through Gribbin's cogent summary of the forces shaping earth's climate, and distinguishes it from the many "iffy" conjectures abounding. The arguments he summons are based both on old theories (Milankovich's ice age model) and on very recent data obtained from space probes, sedimentary analysis, statistical studies, and increasingly sensitive computer models. Excitingly, a new central dogma is emerging—that of a changing sun. It appears that the. sun's nuclear furnace may have "gone off the boil" so that the center is 10% cooler than it was, say, 10 million years ago. That, in combination with notable surface fluctuations—sunspot cycles, solar flares, "gusts" of solar wind—would go far to account for the ups and downs of earth's weather. In turn, periodic changes in the shape of earth's orbit, the angle of its tilt, and its constant "wobble" assure that the amount of heat reaching the surface will vary over latitude, season, and century. Thus it is an unstable sun interacting with an unstable earth (and both interacting with the movements of the other parts of the solar system) which ultimately shapes our weather. Not that man is not a factor. Gribbin, more conjectural here, feels that industrial pollution—dust, heat, the greenhouse effect, aerosols—may contribute a warming effect in the years ahead. He is also certain that political solutions must be sought to avoid crop shortages and famine. Subtle and sophisticated in flavor, Gribbin's account is to be commended not only for his emphasis on the astrophysics of climate (his field), but for his understanding of present political realities.