Download Chapter 13 Section 3

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