Printer Friendly

The climate, it is achanging.

Ever since scientists realized that the earth's history is punctuated by fairly regular episodes of glaciation, they have tried to untangle the multitude of forces that could trigger climate change. One idea, called the Milankovitch theory, pins the responsibility on periodic changes in the earth's orbit, which alter the amount of solar radiation received by the planet; variations in the eccentricity, tilt and precession of the earth are thought to drive climate cycles at intervals of roughly 100,000, 1,000 and 23,000 years. The Milankovitch theory has had a controversial past, but within the last decade it has gained wide acceptance. Now, a number of papers further assure the theory a place in the club of forces that govern the earth's climate.

In the September GEOPHYSICAL RESEARCH LETTERS, Atsuyuki Yamamoto at the Osaka Electro-Communication University in Osaka, Japan, and colleagues discovered that the size of mineral grains that had been deposited over the last 260,000 years in Lake Biwa, one of the oldest lakes in the world, rose and fell at the same frequencies as Milankovitch cycles. According to the researchers, the grain size reflects erosion rates, which in turn depend on climate changes such as rainfall, temperature and wind; high precipitation rates, for example, increase erosion and the amount of coarse grains carried to the lake.

In another paper in the Sept. 12 NATURE, John Kutzbach of the University of Wisconsin in Madison and F. Alayne Street-PErrott of Oxford University in England conclude that Milankovitch cycles have been largely responsible for changes in the levels of tropical lakes in the Northern Hemisphere. The researchers used a computer model of the atmosphere to simulate how variations in the earth's tilt changed January and July monsoon circulation and rainfall pattersn over the last 18,000 years. In general, their model agreed with long-term changes observed in the geologic record; shorter fluctuations in lake levels lasting 1,000 years or so still must be explained. Complementing this work, Edward Pokras and Alan Mix of Lamont-Doherty Geological Observatory in Palisades, N.Y., recently found Milankovitch rhythms in the abundance of land-based dust in deep-sea cores taken off the coast of Africa; peaks in such dust correspond to times of arid land conditions.
COPYRIGHT 1985 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Malankovitch theory puts responsibility on periodic changes in earth's orbit
Publication:Science News
Date:Oct 19, 1985
Previous Article:Baby walker warning.
Next Article:No laughing matter.

Related Articles
Getting to the core of climate cycles.
Sun-like stars may offer clues to climate.
Devils Hole heats up debate over ice ages.
Staggering through the Ice Ages: what made the planet careen between climate extremes?
Warming may disrupt pace of seasons.
Climate modelers: go talk to the trees.
Debate smolders over cause of ice ages.
Pinning down the sun-climate connection; solar influence extends beyond warm, sunny days.
Earth in the balance: the faith community will need to step up its role as protectors of creation.
Homegrown energy: as America copes with climate change, many see hope in biofuels.

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters