July 29, 2007
Pop Quiz: Climate Change Answers

Below, the educators explain their answers.


1. b.

2. d.

3. d. Average temperature would near 0F.

4. b. Nitrogen and oxygen, which make up 99 percent of Earth's atmosphere, allow infrared radiation (heat) to pass through.

5. c. In cement making, limestone and other materials composed of calcium carbonate are heated to high temperatures, producing calcium oxide and carbon dioxide. Deforestation is another major human activity that releases carbon dioxide into the atmosphere.

6. c.

7. a. Because most of Earth's land mass is in the Northern Hemisphere, photosynthesis in that hemisphere's spring and summer causes a marked decline in carbon dioxide in the global atmosphere.

8. True. Pre-industrial carbon dioxide levels were about 280 parts per million; the concentration today is 380 parts per million.

9. True.

10. True. Cores drilled from ice sheets in polar regions contain air bubbles that are samples of the atmosphere at the time the ice formed.

11. True. Scientists have found that some kinds of pollution reflect and scatter sunlight, reducing the amount of solar energy reaching Earth. This phenomenon, known as global dimming, may have masked global warming by as much as 50 percent. But other particles, like soot from inefficient coal-burning power plants, absorb sunlight and add to warming.

12. False. Increases in ocean temperatures may already be harming marine species, particularly corals. Some marine life could shift or expand in range. As the oceans absorb excess carbon dioxide, they become more acidic, affecting the shell-making ability of species from tiny plankton to giant clams.


1. False. Earth's orbit brings the planet about 3 percent closer to the sun in winter in the Northern Hemisphere. Seasonal differences are attributable to the tilt of Earth's axis.

2. False. While some synthetic chemicals do thin the ozone layer, this is not considered a principal cause of global warming.

3. True. Greenhouse gases, like water vapor and carbon dioxide, allow sunlight to pass through and warm Earth but prevent some of the resulting heat from radiating back into space.

4. False. Many natural processes influence climate, but most climate scientists have concluded that the buildup of human-generated emissions is responsible for the pronounced warming trend measured since 1950.

5. a. Without the natural greenhouse effect, Earth would be frigid and unlikely to have liquid water or life as we know it.

6. c. Half of all gas molecules that make up air lie within 3.5 miles of Earth's surface. The greenhouse gases keep energy from escaping.


1. True. Evidence suggests temperatures during past interglacial periods sometimes exceeded today's averages, in some cases for at least several thousand years.

2. False. In a very few locations, including parts of Bolivia, Nigeria and the southeastern United States, temperatures decreased in the 20th century.

3. False. NASA monitors El Niņo as part of its climate research. El Niņo is a natural Earth system that is not caused by global warming. It is marked by cyclical episodes of warming water in the tropical Pacific and is associated with changes in precipitation and circulation patterns from Asia to the Atlantic. Scientists still do not know how further warming of the global climate might affect this.

4. True. Ruminant livestock, as a result of their digestive process, contribute 28 percent of methane emissions from human-related activities.

5. False. The United States contributes the most, but China, with the proliferation of coal-fired power plants, is likely to exceed that within a year or two, by some estimates.

6. True. Higher temperatures lead to more active evaporation and precipitation. Over all, higher latitudes are likely to see more and areas near the Equator less. Changing circulation patterns may also lead to declines in some areas.

7. True. But only if farm-grown fuels are produced without using large amounts of fossil fuels. Making them can consume almost as much energy as the resulting ethanol contains. Using ethanol and biodiesel also releases carbon dioxide into the atmosphere. But they are renewable energy sources and burn more cleanly than fossil fuels.

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