Frontiers in Earth Science Study Guide
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.
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