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Chapter 13 Section 3 Global Warming Environmental Science Spring 2011 Objectives • Explain why Earth’s atmosphere is like the glass in a greenhouse • Explain why the carbon dioxide content of the atmosphere is increasing • Identify one possible explanation for the increase in average global temperature • Describe what a warmer Earth might be like Bell Ringer • Explain why Earth’s atmosphere is like the glass in a greenhouse ▫ Earth’s atmosphere traps heat which is like a greenhouse trapping heat ▫ The glass lets light through easily, light changes into heat energy, the heat is not as easily able to pass through the glass as the light can ▫ Light continues to come in, heat cannot get out ▫ Heat builds up The Greenhouse Effect • Sunlight streams through atmosphere and heats Earth • As heat radiates from Earth’s surface, some escapes into space • The rest of the heat is absorbed by gases in the troposphere and warms the air ▫ Called Greenhouse Effect The Greenhouse Effect • Greenhouse gases: gases that absorb and radiate heat ▫ Water vapor, carbon dioxide, chlorofluorocarbons, methane, and nitrous oxide ▫ Water vapor and carbon dioxide account for most of absorption of heat that occurs in atmosphere Measuring CO2 in Atmosphere • Levels of CO2 vary with seasons • Summer: plants use more CO2 for photosynthesis than the release in respiration ▫ Causes CO2 levels to decrease • Winter: drying grasses and fallen leaves decay and release carbon that was stored ▫ Causes CO2 levels to increase Rising CO2 Levels • After only a few years of measuring CO2 levels, it was obvious they were changing in other ways than just seasonal fluctuations • CO2 levels have increased by over 20% in less than 50 years • Due largely to CO2 released into air when fossil fuels burned Greenhouse Gases and the Earth’s Temperature • Because greenhouse gases trap heat near the Earth’s surface, more greenhouse gases in the atmosphere will result in an increase in global temperature • Comparison of CO2 in atmosphere and average global temperatures for the past 400,000 years supports this view Global Warming • Global warming: average temperature at Earth’s surface increased during the twentieth century • Temperature is rising at a similar rate to the increase in greenhouse gases in the atmosphere • Hypothesized that the increase in greenhouse gases has caused the increase in temperature Consequences of a Warmer Earth • Melting ice, rising sea levels • Global weather patterns ▫ Severe weather increasing ▫ Change in ocean current patterns • Human health problems • Agriculture ▫ Frequency of droughts, demand for irrigation • Effects on Plants and Animals ▫ Range of species, migration and nesting patterns Recent Findings • IPCC findings ▫ Average global surface temperature increased by 0.6 degrees C during the 20th century ▫ Snow and ice cover has decreased ▫ Average global sea level has risen ▫ Concentrations of greenhouse gases have continued to increase as a result of human activity ▫ Predicts that human influences will continue to change the composition of the Earth’s atmosphere throughout the 21st century Reducing the Risk • Kyoto Protocol: requires developed countries to decrease emissions of carbon dioxide and other greenhouse gases by an average of 5 percent below their 1990 levels by 2012 • USA decided to not ratify Kyoto Protocol