Frontiers in Earth Science Study Guide (page 2)

Updated on Sep 26, 2011

What Will Happen to the Thermohaline Circulation as the Earth Warms?

This topic is related to the issue of feedbacks just described. But it is broken out as a separate heading because it brings the ocean into the question of global warming. The thermohaline circulation is the plunging of cold, salty water to the depths of the world ocean, primarily from the North Atlantic and around Antarctica. If the thermohaline circulation changes due to global warming, then the warm surface water that is driven toward the poles to replace the surface water that is lost in the downward plunge of the thermohaline circulation will stay nearer to the equator. In one potentially real scenario, the Gulf Stream could diminish, and, paradoxically, northern Europe, which is now warmed by the Gulf Stream, could grow colder even as the rest of the world grows warmer. The dynamics of the thermohaline circulation are not yet well enough known to make a prediction about its future under a changed climate.

What Caused the Ice Ages?

It is now more than 160 years since geological evidence first emerged that great ice sheets had once covered almost all of Canada and even parts of the northern United States (and that's just the Western Hemisphere). But scientists do not have a definite, precise theory of the ice ages. It is known that ice ages are partially driven by changes in the sun due to changes in Earth's orbit. There are three major changes in Earth's orbit: The orbit can become more or less elliptical, the tilt of Earth's axis can change from more to less, and the position of the seasons can shift along the narrow and wide portions of Earth's elliptical path. These changes each occur in definite cycles, with periods that vary from 100,000 to about 20,000 years.

But during the coldest part of the last ice age, about 20,000 years ago, the sun received by Earth was close to that of today's distribution. So something else is going on. Ice cores have revealed that CO2 was lower in the air back then, therefore, the greenhouse effect was reduced and the lower amount of CO2 contributed to the cooling. But what caused this lower CO2? Practically speaking, it will be important to understand the ice ages in order to gain a better understanding of Earth's future. After all, if we do not fully understand the past, how can we predict the future?

Can We Predict Earthquakes?

The great earthquake in December 2004, took the world by surprise. Not only was the earthquake not predicted, but the possibility of the resulting giant tidal waves in the Indian Ocean had not been anticipated. More than 100,000 people died, mostly in Indonesia. Earthquakes occur from sudden jerks in the friction locked edges of two continental plates. Why can't we predict earthquakes better? Progress has been made, but there is a long way to go. Part of the problem, obviously, is that we have a difficult time seeing what is going on at the edges of the continental plates. But the waves that result from earthquakes provide clues to what is underneath. There is hope for better predictions in the future.

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