Essential Environment: The Science behind the Stories (3rd Edition)

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Chapter 18 Testing Your Comprehension 1 Approximately 30% of incoming solar radiation is reflected back into space, and the other 70% is absorbed by the atmosphere or Earth’s surface. Outgoing heat radiation from the surface is absorbed by greenhouse gases in the lower atmosphere, and then reradiated, warming the air. 2 Although carbon dioxide has a lower global warming potential than some other greenhouse gases, its abundance in the atmosphere gives it the most influence over climate of all gases whose concentrations are being increased by human activity. Water vapor is a greenhouse gas. Increased atmospheric water vapor could increase atmospheric warming by absorbing more outgoing infrared radiation, which would cause more evaporation and therefore more atmospheric water vapor, creating a positive feedback loop. However, it could also increase atmospheric reflectivity of incoming visible- wavelength solar radiation, which would result in less solar energy penetrating the atmosphere to warm the surface, thereby cooling the surface—a negative feedback effect. 3 The ancient atmosphere can be studied by extracting trapped air bubbles from cores bored through layers of accumulated ice in the polar ice caps and ice sheets. 4 Coupled general circulation models (CGCMs) have been effective aids in climate prediction, and results from them form the basis for most of the predictions in the influential IPCC assessment reports. Climate models work by modeling the physics of the transfer of matter and energy in the ocean-atmosphere system. Modelers use known observed data to set parameters that enable the simulation and projection of future data. 5 Figure 18.12 lists many observed and predicted trends in climate and their impacts. Among these, five observed (current or past) trends include: (1) Earth’s average surface temperature has risen 0.74 °C (1.33 °F) in the past 100 years; (2) sea level rose by an average of 17 cm (7 in.) in the 20th century; (3) ocean water became more acidic by about 0.1 pH unit in the past century; (4) arctic areas have warmed the fastest of all regions; and (5) precipitation has increased in a number of regions (e.g.,
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EOC_ch18 - Chapter 18 Testing Your Comprehension 1...

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