Climate Change: What We Know and What We need To Learn

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Climate Change What We Know and What We need To
Learn

• Science on Saturday
• March 26, 2006
• Dave Bader, LLNL
• Barry Marson, Tokay High School
• UCRL-PRES 220136
• Work supported by the Office of Science, US
  Department of Energy ay the University of
  California Lawrence Livermore National Laboratory
  Under Contract W-7405-Eng-48

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Climate Change What Do We Know?Joint science
academies statementGlobal response to climate
change June 2005(http//nationalacademies.org/on
pi/06072005.pdf)Signed by the Presidents of the
National Science Academies of

• Italy
• Japan
• Russia
• United States
• United Kingdom

• Brazil
• Canada
• China
• France
• Germany
• India

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Climate change is real

• The evidence comes from direct measurements of
  rising surface air temperatures and subsurface
  ocean temperatures and from phenomena such as
  increases in average global sea levels,
  retreating glaciers, and changes to many physical
  and biological systems.
• It is likely that most of the warming in recent
  decades can be attributed to human activities.
• This warming has already led to changes in the
  Earth's climate

.
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What is Climate?

• Simplest definition The average weather
• More complicated answer The statistics of
  weather at a location or over a defined area
• Weather
• Is it raining now?
• The temperature outside.
• There is a snowstorm in Reno.
• Climate
• The average temperature for Pleasanton in July
• The average yearly snowfall in Yosemite
• The probability that there will be another flood
  in Napa next winter

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Weather vs Climate
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Weather and Climate are Driven by the Earths
Energy and Water Cycles

• The sun transfers energy to the earth (warming)
• The earth transfers energy to outer space
  (cooling)
• The heating and cooling is unevenly distributed
  over the Earths surface
• Atmospheric motions (weather) and ocean
  circulations result from this uneven heating and
  cooling

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The Suns Energy Drives the Climate
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Demonstration 1

• IR Thermometer

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Visible and Infrared Satellite images of the
Western Hemisphere
Energy In
Energy Out
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Greenhouse Gases Affect the Infrared Radiation
Part of the Energy Balance

• Greenhouse Gases absorb some of the energy
  radiated from the surface and release heat to the
  air
• Primary Greenhouse Gases are CO2 , O3 and water
  vapor
• CO2 evenly distributed throughout the troposphere
  and slowly increasing
• Water vapor highly variable in space in time, but
  total is nearly constant
• O3 nearly constant in stratosphere, highly
  variable in troposphere

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Annual Average Energy Budget Terms
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Incoming and Outgoing Energy Budget Differences
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Heat Transport

• Atmosphere
• Warm air rises, cold air sinks (warm air is less
  dense)
• Water absorbs heat when it evaporates and melts,
  releases heat when it condenses and freezes
• Motions are influenced by the Earths rotation
• All weather results from these processes
• Minutes to weeks
• Ocean
• Ocean circulations result from differences in
  salinity and temperature
• Ice is less dense than water
• 4 C water is most dense
• Warm fresher water rises, cold salty water sinks
• Motions are influenced by the Earths rotation
• Days to centuries

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Demonstrations

• Air convection
• Water convection
• Evaporative cooling

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Source IPCC 2001
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Quicktime Ocean clip available athttp//sos.noaa
.gov/movies/index.htmlunder Sea Current
Simulation
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Average Circulation
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Atmosphere is Thin Shell Surrounding the Earth
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Most of the Mass and Water in Troposphere (lowest
15 km)
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Water Cycle
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Thunderstorm Convection
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Animation available at http//www.vets.ucar.edu/
vg/CCM3T170/index.shtml
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Climate Change is Caused by Changes in the Energy
Balance
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Climate Change ResearchWhat We Need to Learn

• System is unobservable over the time scales
  required for experiments decades to millenia
• Models are substitutes numerical laboratories
• Effects of a small change have big impacts from a
  human perspective
• Very complex problem because of feedbacks
• Positive Feedback Examples
• Snow-Ice Cooling
• Water Vapor Warming
• Negative Feedback Examples
• High Cloud Cooling

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Natural Climate Change

• Large volcanic eruptions eject tiny dust
  particles into the stratosphere that stay
  suspended for several years and reflect sunlight
• Changes in the amount of sunlight received by
  Earth
• Orbital changes occur slowly over hundreds of
  centuries
• Solar output cycles produce small changes over a
  few years, e.g.sunspots

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Annual Average Energy Budget Terms
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Ice Ages

• At the peak of the last ice age (18,000 years
  ago), the temperature was only 4-5 C colder than
  it is today, and glaciers covered much of North
  America!

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Greenland Ice Sheet
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Anthropogenic Climate Change

• Earths energy budget changed rapidly since the
  mid-1800s because of human activities
• Emissions of CO2 from fossil fuel combustion
• Increased from 270 ppm in the 1800s to over 370
  ppm today
• Estimates are that 90 of warming since 1850
  results from the radiative effects of CO2
  concentration increases
• Air pollution of other gases and small aerosol
  particles
• Changes in land use
• Farms replace forests
• Urbanization
• Many others

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Annual Average Energy Budget Terms
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Carbon Dioxide and Temperature
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(No Transcript)
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Changes in Ocean Temperature
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Snow line elevation increases and alpine glaciers
melt
Much of the world depends on snowpack for water
storage. Winter snows support summertime
irrigation
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Impacts of Climate Change
(- )
(- )

• Snowpack Temperature
• Observed Change 1950-1997

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Future Climate Change?

• CO2 Greenhouse Gas Warming Theory is over 100
  years old (1896). Postulated that doubling of
  concentrations would result in 5-6 C global
  surface temperature rise.
• Changes observed are consistent with theory
• Nighttime temperatures increase more than daytime
• Polar regions warm faster than tropical regions

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Approximations Assumptions (errors)
Approximations Assumptions (errors)
Approximations Assumptions (errors)
Computer code DO K1,NZ U(I,J,K)U(I,J,K)DELU(K)
ENDDO
Numerical model DYF(Dx,Dy,Dz ,Dt )
Approximations Assumptions (errors)
Experiment design DELX100.,DELY100,..
Modeled System
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Test Models with Observations
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(No Transcript)
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What Happens Next?

• CO2 concentrations will continue to increase
• Rate and amount depend on energy sources and
  consumption and natural processes
• Model simulations suggest that increasing CO2
  concentrations to 540 ppm will raise global
  temperatures 1.7-4.1C
• Climate will continue to change
• Feedbacks unknown and potentially large
• Ice-free summertime Arctic Ocean?
• Melting of Ice Sheets
• Melting of Greenland Ice Sheet will raise
  sea-level 7 meters (23 feet)

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Sea-ice from Climate Model
Animation available at http//www.vets.ucar.edu/v
g/categories/globalchange.shtml
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Sea-Ice and Climate Change