Chapter 3 Notes

Chapter 3 Notes - Chapter 3—The Chemistry of Global...

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Chapter 3—The Chemistry of Global Warming 25 March 2008 3.1—In the Greenhouse: Earth’s Energy Balance -The beautiful blue-green ball we inhabit has an average annual temperature of 15 ° C (59 ° F). -Both Venus and Earth are warmer than one would expect based solely on their distances from the Sun and the amount of solar radiation they receive. If distance were the only determining factor, the temperature of Venus would average approximately 100 ° C, the boiling point for water. Earth, on the other hand, would have an average temperature of -18 ° C (0 ° F), and the oceans would be frozen year round. -Greenhouse gases are gases capable of absorbing and reemitting infrared radiation into the atmosphere. There has been a steady increase in the amount and reliability of data gathered about the role that CO 2 in the atmosphere has increased over the past 150 years, and we know that Earth’s average temperature has not remained constant. -Of the incoming solar radiation, about 30% is reflected by the molecules that make up our envelope of air, by the clouds and dust in the atmosphere, or by Earth itself. Another 25% is absorbed in the atmosphere, leaving about 45% to be absorbed by the continents and oceans and warming them. Earth, in turn, radiated some of its absorbed energy back into the atmosphere, where greenhouse gases such as H 2 O and CO 2 are very efficient absorbers of this longer-wave IR radiation. -The greenhouse gas molecules found in our atmosphere absorb and scatter most of the radiation in all directions. Much of this heat is redirected and comes back though the lower regions of our atmosphere toward the Earth, rather than being lost to space. -Taking all processes together, about 81% of the energy radiated by Earth is trapped by greenhouse gases and does not directly escape to space. The greenhouse effect is the process by which atmospheric gases trap and return a major portion of the heat (infrared radiation) radiated by the Earth. -Without the protective later of our atmosphere, Earth could become very hot from incoming radiation. Without the atmosphere’s ability to reflect Earth’s radiated heat back toward the surface, our lovely orb could become an ice planet because of the direct loss of heat into space. The current average temperature of our planet, about 15 ° C (59 ° F) is about 33 ° C warmer than what would be expected from its distance form the Sun. It is also much higher than the -270 ° C of outer space. 3.2—Gathering Evidence: The Testimony of Time -In the 4.5 billion years that out planet has existed, its atmosphere and climate have varied widely. Evidence from the composition of volcanic gases suggests the concentration of carbon dioxide in Earth’s early atmosphere was perhaps 1,000 times greater than it is today. Much of the CO 2 that dissolved in the oceans became incorporated in rocks such as limestone, which is calcium carbonate, CaCO 3 . High concentrations of carbon dioxide all those years ago also made possible a significant
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Chapter 3 Notes - Chapter 3—The Chemistry of Global...

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