Download Air: Climate

Air: Climate
Objectives
• Analyze human contributions to global climate change and what effects our
modifications are having on physical and biological systems
• Briefly discuss policy options for responding to the threats of global climate
change
• Summarize the structure and composition of the atmosphere
• Explain some basic weather patterns
• Comprehend how El Niño cycles change ocean surface temperatures and
affect continental climate
Human-induced global climate change
Is global climate changing?
 Global average surface temperature rose 0.6o C during 20th century
 Ten hottest years have been since 1990
 Average summer and winter temperature in Alaska are 4°C higher than
average
IPCC
• In 1988, the Intergovernmental Panel on Climate Change (IPCC) was formed
 Released third report in February 2001
 700 scientists from 100 countries reviewed results from 3,000 studies
 Recent changes in world’s climate have had discernable impacts on
physical and biological systems
 Human activities are at least partially responsible
IPCC in 2007
• IPCC now recognizes that humans are responsible for global climate change
and that there is even more evidence of effects on biological and physical
systems
Evidence for climate change
• What effect is climate change already having on physical systems?
Evidence for climate change
• What effect is climate change already having on biological systems?
Potential global climate change
International Climate Negotiations
• Kyoto Protocol (1997) - United Nations Pact
 160 nations agreed to roll back carbon dioxide, methane, and nitrous oxide
emissions about 5% below 1990 levels by 2012
 Sets different limits for different countries, depending on prior output
 Developing countries exempted
Kyoto protocol
• 126 nations have officially ratified the agreement
• Bush pulled out of agreement in 2001
• Russia ratified in Fall 2004
• Russia put Kyoto over the limit needed to make protocol come into force
 Has become legally binding for all participants
• Australia ratified in December 2007
 US is the only industrialized country that still refuses to sign
• Kyoto is still probably not enough
Controlling greenhouse emissions
• Reducing carbon dioxide levels
 Renewable energy sources may offer a better solution to climate problems
• Capturing and storing carbon dioxide
 Carbon management
 Planting vegetation
 Emissions trading system
 Deep water injection
 Other countries are doing it!
The atmosphere and climate
• Weather - A description of physical conditions of the atmosphere
• Climate - A description of the long-term weather pattern in a particular area
 Weather and climate are primary determinants of biomes and ecosystem
distribution
Troposphere
• Troposphere
 Ranges in depth from 18 km over the equator to about 8 km over the poles
 Air circulates in convection currents
 Contains 75% of total air mass
A Layered envelope
• Stratosphere
 Extends from troposphere to about 50 km
 Similar composition to troposphere, but much more dilute
 Fraction of water vapor is 1000x less and ozone is 1000x more than in the
troposphere
 Relatively calm
Energy and the greenhouse effect
• Of the solar energy that reaches the outer atmosphere:
 About one-quarter is reflected by clouds and the atmosphere
 Another quarter is absorbed by carbon dioxide water vapor, ozone and a
few other gases
 About half reaches the earth’s surface
Energy and the greenhouse effect
• Most solar energy reaching the earth is visible light
 Energy reemitted by the earth is mainly infrared radiation (heat energy)
 Longer wavelengths are absorbed in the lower atmosphere, trapping
heat close to the earth’s surface
 Greenhouse Effect
Energy balance
Water stores heat and winds redistribute it
• Water vapor contains a large amount of energy stored as latent heat
• Uneven heating produces pressure differences that cause wind, rain, and
storms (weather), which redistribute heat and water
Convection currents
Convection currents
• Major zones of subsidence occur at about 30o north and south latitude
 Where dry, subsiding air falls on continents, it creates desert regions
Coriolis Effect
• Surface flows do not move straight north and south, but are deflected due to
Coriolis Effect
 Steady, reliable wind patterns are created
Convection Cells and Prevailing Winds
Ocean currents
• Warm and cold ocean currents strongly influence climate conditions on land
Upwelling
• Upward movement of water along a coast; replaces surface waters that move
away from shore
Seasonal Winds
• Monsoon - Seasonal reversal of wind patterns caused by differential heating
and cooling rates of oceans and continents
Climate Change
• Periodic weather cycles detected
 Milankovitch Cycles - Periodic shifts in earth’s orbit and tilt
 Change distribution and intensity of sunlight reaching the earth
 Sunspot cycles
 El Nino Southern Oscillation
El Niño (ENSO)
• El Niño Southern Oscillation
• Climactic event that involves changes in sea surface temperature and air
circulation patterns in the equatorial Pacific Ocean
ENSO
• Large pool of warm surface water in Pacific Ocean moves back and forth
between Indonesia and South America
 Most years, the warm water is held in western Pacific by steady equatorial
trade winds
 Every three-seven years the trade winds stop and the mass of warm
surface water surges back east
 El Nino year
Between ENSOs
• Warm water and heavy rainfall move west across the Pacific
• Warm moist air rises in the western Pacific causing storms
• Upwelling of cool water along western coasts
During an ENSO
• Trade winds weaken and warm water flows east across the Pacific
• Sea surface temperatures rise
• Upwelling along western coasts ceases
• Heavy rainfall occurs along coasts, droughts elsewhere
 El Niño from 1991-1995 caused floods of the century in Mississippi Valley