National Teach-In on Global Warming

http://people.sfcollege.edu/greg.mead/globalclimate/globalclimateteachin.htm
4 Topics:

1. Controls on global temperature
2. History of our knowledge of greenhouse processes
3. Physics of the Greenhouse Effect
   
4. History of temperature change

Controls on global temperature

• Solar Insolation
  
• Mostly in the Visible Light range:
  
  
• Averages ~250 watts/m² 
• may reach 1000 watts/m² in the tropics with the sun high over head.
• will vary with latitude, season, cloud cover, and other factors.
  
• Long term changes as Sun ages.
• Short term changes due to sunspot cycles.
  
• (From Sky and Telescope, 3/09, Vol 117, #3, p. 33)
  
  
• Albedo
• currently ~30%.
• lower during periods of high sea level.
• higher during ice ages.
  
  
• Plate Tectonics
• Mountain Building changes atmospheric circulation
• Uplift of Himalayas - may have kick-started Antarctic Glaciation ~33 MYA.
  
• Movement of Continents alters oceanic circulation
• Northward movement of South America away from Antarctica allowed isolation of Antarctica, leading to cooling.
  
  
• Orbital Variations (Milankovitch Cycles)
• 
  
• Changes distribution and (slightly) amount of solar heating.
• Controlled Ice Ages over the last 2.5 MY.
  
• Had other effects on climate earlier.
  
  
• Volcanic Eruptions
• Ash blocks sunlight.
• SO₂ emitted - reverse greenhouse gas.
  
• CO₂ emitted.
• generally fairly short term <10 yrs.
  
  
• Greenhouse Effect:
• A necessary part of our planet.
• Global average temperature ~15^oC (~59^oF).
• Without greenhouse effect, ~-18^oC (~0^oF).
  
• Greenhouse Gases
  
• Water
• in vapor (atmospheric humidity) form.
• not in droplet form (clouds and precipitation).
• about 80% of the total global Greenhouse Effect.
  
• CO₂
• about 20% of the total global Greenhouse Effect.
• Has increased ~35% in last 150 years (from ~280ppm to ~380ppm).
  
• Weathering - uses up CO₂ in chemical reactions.
  
• Tied to Plate Tectonics because mountain building increases weathering rates, especially in the Himalayas.
  
• Plant Growth - uses up CO₂.
• Deforestation - releases CO₂ as decay occurs.
• Sea Level drop - allows plant growth.
• Sea Level rise - kills forests, decay releases CO₂.
• Formation of Limestone (CaCO₃) removes CO₂.
• ~100,000x more CO₂ in limestone than in atmosphere
• Volcanic activity - releases CO₂.
• Oceanic Productivity - transfers organic material to deep ocean.
• Oceanic temperature change
• cold water can hold more CO₂.
• warm water can hold less CO₂.
• about 60x more CO₂ in ocean than in atmosphere.
• Use of fossil fuels - releases CO₂.
• Petroleum - preserved marine algae.
• Coal - preserved land plants.
• ~600x more CO₂ in fossil fuels than in atmosphere.
• Methane
• much more effective than CO₂ (molecule for molecule).
• much less abundant.
• overall minor effect.
  
• has doubled in last 150 years.
• stored as
• Fossil Fuels.
• Methane Hydrates (USGS site).
• stores ~2x amount of carbon as in Fossil Fuels.
• stored in continental margin sediments.
• pressure and temperature sensitive.
• possibly an important energy resource.
  
• released by bacterial activity:
• termites.
• cattle and other animals' digestive tracts.
  
• rice patties.
• degassing from oil drilling?
  
• naturally destroyed or stored by:
• oxidation in atmosphere.
• combustion.
• methane hydrate deposition.
  
• Ozone (in stratosphere only)
• CFC's (ChloroFluoroCarbons)
  
• NO₂ (Nitrous Oxide)
  
• All of these interact:
  

  (from Ruddiman, W.F., 1997 Tectonic Uplift and Climate Change)

  
  

(Very brief) History of our knowledge of greenhouse processes

• Joseph Fourier (1824, 1827) first discovered the greenhouse effect
  
• From the American Institute of Physics
• John Tyndall (1820-1893) described the effect in 1861
• Svante Arrhenius (1859-1927, Nobel Prize winner, Chemistry, 1903) predicted global warming in 1896 due to anthropogenic CO₂.
• How good is our knowledge about Global Climate Change?
  
• Statements on Global Warming

Physics of Greenhouse Effect

• 
• (from http://ipcc-wg1.ucar.edu/wg1/FAQ/wg1_faq-1.3.html)

Key Points about Climate and Global Warming:

• Climate:
• A long term average (30 yrs according to NWS)
• Lots of rapid variations
• The Earth has been hotter - and will be again.
• The Earth has been colder - and will be again.
• We don't know everything about it
• We do know alot about it.
• Global Warming
  
• It is a long-term change -
• It does not mean that every location on earth will heat up steadily -
• It is not a direct control on individual weather patterns -
• It does not mean that the increase will be steady-
• We don't know everything about it
• We do know alot about it.

History of temperature change
Evidence:

• Paleontological
• Sedimentological
• Isotopic
• Oxygen Isotopes in shells and limestones give ice volume and temperature.
• Oxygen and Hydrogen Isotopes in ice cores give ice volume and temperature.
• Carbon Isotopes in shells and limestones give biological productivity and sequestration.
• Ice Cores:
• Isotopic evidence.
• Volcanic ash and acid.
• Palynological.
• Atmospheric gas composition.
• Direct Measurements (for less than 200 years)
  

Long term:

This graph shows approximate changes over the last 500 million + years.  Note that there have been periods much warmer and significantly cooler than today.  These temperature changes have occurred for a large variety of reasons.  Plate Tectonics undoubtably controls many of the changes, through changing ocean currents and changes in weathering. (Also see http://www.scotese.com/climate.htm; Christopher Scotese, UT Arlington)

Cenozoic (the last ~65 million years)

• 
  
• PETM:
• Possible runaway greenhouse effect
• possibly due to destabilization of Methane Hydrates
• Antarctic Glaciation
• Increased weathering of Himalayas?
• Opening of Drake Passage?
• Antarctic Reglaciation
• Uplift of Himalayan Plateau?
  
• Pliocene/Pleistocene glaciation
• Uplift of Rocky Mountains causing changes in Jet Streams?
• Changes in oceanic circulation?
  

Plio-Pleistocene:
Ice ages

• The last 2.5 million years:

(From 2003 Royal. Soc. Chemistry newsletter)

• The last 650,000 years

(from http://www.realclimate.org/index.php?p=221, ice core data from Antarctica)

The Last 2000 years:

Recent:

(From Robert A. Rohde, UC Berkely, based on publically available temperature data)

CO2 Records: from ice cores, from direct measurements.

(From: IPCC)


(data from Dave Keeling and Tim Whorf, Scripps Inst. of Oceanography)


(From Sky and Telescope, 3/09, Vol 117, #3)  - Short answer, NO.

Why are we concerned?

1. Warming of climate systems
2. Melting of glacial systems
• sea level rise (moderate if best case scenario)
  
• glacial surges (could lead to more rapid sea level rise)
  
3. Warming of Oceans
4. Feedbacks:
1. Warming of atmosphere leading to warming of oceans, causes lowered CO₂ solubility, leading to CO₂ leaving the ocean, leading to increased greenhouse effect, leading to more atmospheric warming...
2. Warming of atmosphere leads to melting of glaciers, leading to lowered albedo, leading to more absorption of solar radiation, leading to more warming...
3. Warming of ocean leads to methane hydrates converting back to gaseous methane, leading to increased greenhouse effect, leading to more warming...
4. Rising sea level covers land, leading to forest destruction, leading to decay of organic matter, leading to more release of CO₂, leading to more warming...