1. Atmosphere and Climate ChangeSection 3 Objectives Explain why Earth’s atmosphere is like the glass in a greenhouse. Explain why carbon dioxide in the atmosphere appears to be increasing. Identify one possible explanation for the increase in average global temperature. Describe what a warmer Earth might be like.

2. Atmosphere and Climate ChangeSection 3 The Greenhouse Effect Earth is somewhat comparable to a greenhouse. Earth’s atmosphere acts like the glass in a greenhouse. Sunlight streams through the atmosphere and warms Earth. As this energy in the form of heat radiates up from Earth’s surface, some of it escapes into space. The rest is absorbed by gases in the troposphere and warms the air. This process of warming Earth’s surface and lower atmosphere is called the greenhouse effect.

3. Atmosphere and Climate ChangeSection 3 The Greenhouse Effect

4. Atmosphere and Climate ChangeSection 3 The Greenhouse Effect Not every gas in our atmosphere reradiates infrared radiation in this way. A greenhouse gas is a gas that absorbs and reradiates infrared radiation from the sun. The major greenhouse gases are water vapor, carbon dioxide, methane, and nitrous oxide. Of these, water vapor and carbon dioxide account for most of the absorption of that occurs in the atmosphere.

5. Atmosphere and Climate ChangeSection 3 Measuring Carbon Dioxide in the Atmosphere In 1985, a geochemist named Charles Keeling installed an instrument at the top of a tall tower on the Mauna Loa observatory in Hawaii. Keeling wanted to precisely measure the amount of carbon dioxide in the air, far from forests and cities where carbon dioxide levels vary every day.

6. Atmosphere and Climate ChangeSection 3 Measuring Carbon Dioxide in the Atmosphere The winds that blow steadily over Mauna Loa have come thousands of miles across the Pacific Ocean, far from most forests and human activities, swirling and mixing as they traveled. Keeling reasoned that at Mauna Loa, the average carbon dioxide levels for the entire Earth could be measured.

7. Atmosphere and Climate ChangeSection 3 Measuring Carbon Dioxide in the Atmosphere Much of the carbon dioxide that is released into the air dissolves in the ocean or is used by plants for photosynthesis. During the summer, growing plants use more carbon dioxide for photosynthesis than they release in respiration, causing the levels to drop. In the winter, dying grasses and fallen leaves decay and release the carbon that was stored in them, causing levels to rise.

8. Atmosphere and Climate ChangeSection 3 Rising Carbon Dioxide Levels After a few years of measurement, it was obvious that the levels were undergoing changes other than seasonal fluctuations. Each year, the high carbon dioxide levels of winter were higher, and each year, the summer levels did not fall as low. Since 1958, the level of carbon dioxide in the atmosphere has increased by over 20 percent. This increase is due largely to the burning of fossil fuels.

9. Atmosphere and Climate ChangeSection 3 Rising Carbon Dioxide Levels

10. Atmosphere and Climate ChangeSection 3 Greenhouse Gases and Earth’s Temperature Most scientists think that because greenhouse gases absorb and rerelease infrared radiation to Earth’s surface, more greenhouse gases in the atmosphere will result in an increase in global temperature. A comparison of carbon dioxide in the atmosphere and average global temperatures for the past 400,00 years supports this view.

11. Atmosphere and Climate ChangeSection 3 Greenhouse Gases and Earth’s Temperature Today, we are releasing more carbon dioxide than any other greenhouse gas into the atmosphere. Millions of tons of carbon dioxide are released into the atmosphere each year from power plants that burn coal or oil, and cars that burn gasoline. Millions of trees are burned in tropical rainforest to clear the land for farming. The amount of greenhouse gases including carbon dioxide, methane, and nitrous oxide in the atmosphere is increasing.

12. Atmosphere and Climate ChangeSection 3 Greenhouse Gases

13. Atmosphere and Climate ChangeSection 3 Global Climate Change Global warming is a gradual increase in the average global temperature. Because the rise in temperature correlates to the increase in greenhouse gases in the atmosphere, most scientists conclude that the increase in greenhouse gases, and other factors, have caused the increase in temperature. Earth’s average global temperature increased during the 20th century and many scientists predict that this warming trend will continue. Thousands of experiments and computer models support this hypothesis.

14. Atmosphere and Climate ChangeSection 3 Global Climate Change

15. Atmosphere and Climate ChangeSection 3 Global Climate Change Temperatures are not necessarily rising at a constant rate, or rising in all parts of the world. As with changes in carbon dioxide levels, short-term variations in temperature are superimposed on larger trends such as changes in patterns of precipitation, frequency of fires, and extreme weather events. So, most scientists use the term global climate change rather than global warming.

16. Atmosphere and Climate ChangeSection 3 Modeling Climate Change Predictions about climate change are based on computer models. Scientists use mathematical relationships among “drivers,” such as solar input, wind patterns, and cloud cover and “response variables,” such as troposphere temperature, sea surface temperature, ice cover, and sea level. These relationships are expressed as equations within complex models.

17. Atmosphere and Climate ChangeSection 3 Modeling Climate Change The resulting models can be used to predict how factors such as temperature will be affected. Scientists validate the models by starting with historical conditions and then comparing model projections to know changes in climate. The models are constantly being updated with new information. About a dozen different models similarly predict widely increasing temperatures that are not simply driven by natural climate or solar variability. Humans are playing some role in climate change.

18. Atmosphere and Climate ChangeSection 3 The Consequences of a Warmer Earth In North America, some birds are nesting two weeks earlier than they did 50 years ago. In Britain, many plants are flowering up to 55 days earlier in the year than they did 40 years ago. The possible effects of climate change include a number of potentially serious environmental problems, such as changes in weather patterns and rising sea levels. The possible effects of a warmer Earth will not be the same everywhere and countries will vary in their ability to respond.

19. Atmosphere and Climate ChangeSection 3 Rising Sea Levels Sea level has been measured in many locations over the past 100 years. Sea levels are rising and will continue to rise. Sea levels rise because as water warms, it expands. Also, ice that is currently over land is melting and the water is flowing into the ocean. The rise is sea levels could flood coastal wetlands and other low-lying areas. Beaches could be eroded, the salinity of bays and estuaries, and coastal freshwater aquifers might increase, negatively affecting aquatic life and decreasing freshwater resources.

20. Atmosphere and Climate ChangeSection 3 Global Weather Patterns If the Earth warms up significantly, the surface of the oceans will absorb more energy in the form of heat, which may make hurricanes and typhoons more intense. Some scientists are concerned that climate change will also cause a change in ocean current patterns, such as slowing of the Gulf Stream. Such a change could significantly affect the world’s weather. Severe flooding could occur in some regions at the same time droughts and fires devastate other regions.

21. Atmosphere and Climate ChangeSection 3 Human Health Problems Greater numbers of-heat related deaths could occur. Since trees and flowering plants would flower earlier and for longer than they do win, people who are allergic to pollen would suffer from allergies for more of the year. Warmer temperatures could enable mosquitoes, vectors of diseases such as malaria and Dengue Fever, to establish themselves in areas that are too cold for them currently.

22. Atmosphere and Climate ChangeSection 3 Agriculture Agriculture would be most severely impacted by climate change if extreme weather events, such as drought, became more frequent. Higher temperatures could result in decreased crop yields. As a result, the demand for irrigation could increase, which would further deplete aquifers that have already been overused.

23. Atmosphere and Climate ChangeSection 3 Effects on Plants Climate change could alter the range of plant species and could change the composition of plant communities. A warmer climate could cause trees to colonize northward into cooler areas. Forests could shrink in areas in the warmer part of their range and lose diversity. Increased frequency of fires may shift whole ecosystems.

24. Atmosphere and Climate ChangeSection 3 Effects on Animals Climate change could cause a shift in the geographical range of some animals. For example, Northern birds may not have to migrate as far south during the winter. Warming of surface waters of the ocean might cause a reduction of zooplankton, tiny shrimp-like animals, that many marine animals depend on for food. Warming tropical waters may kill algae that nourish corals, thus destroying coral reefs. As more carbon dioxide dissolves into oceans, the water could become more acidic, which could disrupt food webs.

25. Atmosphere and Climate ChangeSection 3 Recent Findings The International Panel on Climate Change (IPCC) issued its Fourth Assessment Report (FAR) in 2007 that described what was currently known about about the global climate system and provided future estimates. The IPCC reported that the average global surface temperature increased by 0.74ºC since their third report in 2001. The temperature increase is both global and higher at northern latitudes. Also, the average global sea level continues to rise, and the concentrations of atmospheric greenhouse gases have continued to increase as a result of human activities.

26. Atmosphere and Climate ChangeSection 3 Reducing the Risk The need to slow global climate change has been recognized by the global community. Some nations and organizations have engaged in reforestation projects to reduce carbon dioxide. However, the attempt to slow global climate change is made difficult by the economic, political, and social factors faced by different countries.

27. Atmosphere and Climate ChangeSection 3 Reducing the Risk Conflict has already arisen between developed and developing countries over future CO 2 emissions. Developing countries are projected to make up half of all CO 2 emissions by 2035.

28. Atmosphere and Climate ChangeSection 3 Reducing the Risk The Kyoto Protocol is an international treaty, first negotiated in 1990, in attempt to reduce greenhouse gas emissions. Many countries have ratified the treaty, but not those most responsible for the greatest greenhouse gas emissions, including the United States. Scientists, governments, organizations, businesses, and individuals are trying to find ways to reduce greenhouse gas emissions and address the effects of global climate change.

29. Atmosphere and Climate ChangeSection 3 Reducing the Risk