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Bellringer The Greenhouse Effect • The Earth is similar to a greenhouse. The Earth’s atmosphere acts like the glass in a greenhouse. – Sunlight streams through the atmosphere and heats the Earth. – As this heat radiates up from Earth’s surface, some of it escapes into space. – The rest of the heat is absorbed by gases in the troposphere and warms the air. • This process of heat absorption is called the greenhouse effect. The Greenhouse Effect The Greenhouse Effect • A greenhouse gas is a gas composed of molecules that absorb and radiate infrared radiation from the sun. – These gases include: water vapor, carbon dioxide, CFCs, methane, and nitrous oxide, with water vapor and Carbon Dioxide accounting for most of the radiation absorption. Measuring Carbon Dioxide in the Atmosphere • Charles Keeling, a geochemist installed an instrument to monitor amount of carbon dioxide in the air, far away from forests and cities, at the top of a tall tower on the volcano Mauna Loa in Hawaii. – His reasoning for choosing Manua Loa over a forest or city was that he thought carbon dioxide levels for the entire Earth could be measured instead of individual locations. • In a forest, carbon dioxide levels rise and fall with the daily rhythms of photosynthesis. • Near cities, carbon dioxide from traffic and industrial pollution raises the local concentration of gas. Measuring Carbon Dioxide in the Atmosphere • Keeling’s first measurement, in March of 1958, was 0.0314 percent, over the course of the year the trend was for levels to rise and then fall and the cycle would repeat . – Ex. In summer, growing plants use more carbon dioxide for photosynthesis than they release in respiration, causing the levels to drop. – Ex. In winter, dying grasses and fallen leaves decay and release the carbon that was stored in them, causing levels to rise. Rising Carbon Dioxide Levels • Each year, the high carbon dioxide levels of winter were higher, and each year, the summer levels did not fall as low. • In 42 years, carbon dioxide has gone from 314 to 386 parts per million to an increase of 544 parts per million. This increase may be due to the burning of fossil fuels. Rising Carbon Dioxide Levels Greenhouse Gases and the Earth’s Temperature • Many scientists think as greenhouse gases trap heat near the Earth’s surface, more greenhouse gases in the atmosphere 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 support it. Greenhouse Gases and the 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 plant and car emissions. • Millions of trees are burned in tropical rainforest to clear the land for farming. • We also release other greenhouse gases, such as CFCs, methane, and nitrous oxide, in significant amounts. Greenhouse Gases How Certain is Global Warming? • Global warming is a gradual increase in the average global temperature that is due to a higher concentration of gases such as carbon dioxide in the atmosphere. – Earth’s average global temperature increased during the 20th century and many scientists predict that this trend will continue in the 21st century. How Certain is Global Warming How Certain is Global Warming? • Not all scientists agree that the observed global warming is due to greenhouse gases. – Some believe that the warming is part of natural climatic variability due to widespread fluctuations in temperature have occurred throughout geological time. Modeling Global Warming • Predictions about climate change are based on computer models that predict how phenomena such as temperature, rainfall patterns, and how sea level will be affected. • Hard for scientists to predict because of the variety of factors that play into climate. Modeling Global Warming • Computer modeling is complicated by the Earth’s feedback processes including: clouds, water vapor, ice, changes in ocean chemistry, and changes in vegetation, that sometimes make it necessary to use different equations under changing simulated environments. The Consequences of a Warmer Earth • The impacts of global warming could include a number of potentially serious environmental problems including: • disruption of global weather patterns and a global rise in sea level • adverse impacts on human health, agriculture, and animal and plant populations • other impacts on the environment that could not be predicted by computer models Melting Ice and Rising Sea Levels • If the global temperature increased, the amount of ice and snow at the poles would decrease, causing sea levels around the world to rise. • Coastal wetlands, and other low-lying areas could be flooded causing potential lost of homes and income. • The salinity of bays and estuaries might increase, adversely affecting marine fisheries. Freshwater aquifers could become too salty to be used as sources of fresh water. Global Weather Patterns • If the Earth warms up significantly, the surface of the oceans will absorb more heat, which may make hurricanes and typhoons more common. • concern that global warming will also cause a change in ocean current patterns, shutting off the Gulf Stream • change could significantly affect the world’s weather • Severe flooding could occur in some regions at the same time droughts devastate other regions. Human Health Problems • The number of heat related death could potentially arise. • Very young and very old people would have the greatest risk of heat exhaustion. • Respiratory illnesses, especially in urban areas, increase. • Temperature increases might cause the mosquito population to rise, which carry diseases such as malaria and encephalitis. Agriculture • Agriculture could be severely impacted by global warming if extreme weather events, such as drought, occur more frequently. – Higher temperatures could result in decreased crop yields. • As a result, the demand for irrigation could increase, which would deplete aquifers that have already been overused. 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 causing the southern areas to shrink and lose diversity. Effects on Animals • Global warming could cause a shift in the geographical range of some animals. • Ex. Northern birds may not migrate as far south during the winter. • Warming of surface waters of the ocean might cause a reduction of zooplankton, that many marine animals depend on for food. • Warming tropical waters may kill algae that nourish corals, thus destroying coral reefs. Recent Findings • The International Panel on Climate Change (IPCC) issued its Third Assessment Report (TAR) in 2001. • The IPCC reported that the average global surface temperature increased by 0.6ºC during the 20th century, snow and ice cover has dropped, and the global sea level has risen. • The concentrations of atmospheric gases have continued to increase as a result of human activities and would continue to rise due to this activity throughout the 21st century. Reducing the Risk • The Kyoto Protocol is an international treaty countries signed to agree to reduce their emissions of carbon dioxide and other gases that may contribute to global warming by the year 2012. • In March of 2001, the United States decided not to ratify the Kyoto Protocol. • However, most other developed nations are going ahead with the treaty. Reducing the Risk • The need to slow global warming has been recognized by the global community. – Some nations and organizations have developed reforestation projects to reduce carbon dioxide. • 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. Reducing the Risk