Frontiers in Earth Science Study Guide (page 2)
Indeed, humans have gained a tremendous amount of understanding about planet Earth, through careful observations, precise experiments, and bold theories, particularly in the last 50 years. But many mysteries remain. Solving some of these mysteries is vital to our future. In this final lesson, we look at some of the frontiers of earth science.
How Much Will Earth Warm as Carbon Dioxide Levels Rise?
The atmosphere's CO2 level is about 30% higher than it was prior to the industrial revolution. Most of the increase is from the release of CO2 during the combustion of fossil fuels. Climatologists predict a result of global warming. But how much? The best computer simulations predict a warming of 1.5° to 4° C (roughly 3° to 8° F) when the CO2 doubles, perhaps by the end of the century, depending on the use of fossil fuels. That is a great deal of uncertainty, especially given the magnitude of this critical environmental problem.
One of the causes for the uncertainty in the predictions of global warming is the effect of clouds. We know clouds are accumulations of tiny water droplets in the sky. But many of the details of clouds are not yet known. Clouds are simply too complex. You can see their complexity by simply looking up into the sky. Imagine trying to mathematically describe the formation and shape of a cumulus cloud, with filigrees of white trailing off its sides, which changes almost as you look at it. Yet such mathematical description is what is needed for clouds to be accurately put into the computer models of global warming.
In particular, clouds will act to both warm and cool the earth's surface. Clouds cool the surface because they are white and are good reflectors of sunlight. Clouds warm the surface because they contain water vapor, which is the atmosphere's number one greenhouse gas. Which factor will dominate— warming or cooling—will determine much of the future impact of CO2 on Earth's climate.
A related issue in the difficulty of predicting global warming has to do with the general concept of feedbacks in the climate system. Feedbacks occur when a change in some property of Earth's surface is either positively amplified or negatively dampened and then the changed property interacts with all the other properties. We have seen how the earth's surface has numerous properties: the amount of sedimentary rock, the types of soils, the water cycle, the Hadley cells, ocean gyres, carbon dioxide in the air, ozone, and even humans. Somehow, these interact to form a complex system that we live within, often without much thought about the interactions.
One example of a feedback is the ice-albedo feedback. Albedo is the technical term for reflectivity. Sand, for example, has a higher albedo than does a dark green forest. What about the albedo of ice compared to the darker water underneath? Yes, ice has the higher albedo.
Now, when global warming kicks in, large amounts of sea ice are expected to melt. Some climatologists claim this is happening already. Indeed, a majority of mountain glaciers around the world are receding. If the total area of sea ice declines as a result of CO2–induced global warming, the darker water underneath will be exposed. Darker water absorbs more sunlight than did the ice that formerly covered it. So now the earth would warm even more. This is a positive feedback.
Earth scientists have delineated dozens of potential feedbacks in the climate system. How these various positive and negative feedbacks play out is one of the great unanswered questions in earth science.
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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