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 CO 2 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 CO 2 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 20 th 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 21 st 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