1. Climate Change

2. I. 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. The Greenhouse Effect

4. The Greenhouse Effect
A greenhouse gas is a gas that absorbs and re-radiates 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 that occurs in the atmosphere.

5. A. 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. Measuring Carbon Dioxide in the Atmosphere
Keeling reasoned that at Mauna Loa, the average carbon dioxide levels for the entire Earth could be measured.
Much of the carbon dioxide that is released into the air dissolves in the ocean or is used by plants for photosynthesis.

7. Measuring Carbon Dioxide in the Atmosphere
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. Rising Carbon Dioxide Levels

9. B. 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.
This is causing a global rise in temperature.

10. Greenhouse Gases

11. 2. 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.

12. Global Climate Change

13. Bill Nye climate change video

14. A. 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.

15. Modeling Climate Change
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.

16. 3. The Consequences of a Warmer Earth
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.

17. A. 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 in sea levels will flood coastal wetlands and other low-lying areas.

18. B. Global Weather Patterns
If the Earth warms up significantly, the surface of the oceans will absorb more heat energy, 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.

19. C. 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, 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.

20. D. 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.

21. E. Effects on Plants and Animals
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.

22. F. Effects on Plants and 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.
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23. 4. 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.

24. Reducing the Risk
Conflict has already arisen between developed and developing countries over future CO2 emissions.
Developing countries are projected to make up half of all CO2 emissions by 2035.

25. 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.

26. Reducing the Risk