Natural Causes of Climate Change

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Natural Causes of Climate Change
and

• Past Climates (Paleoclimatology)

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Geologic Time and Human Evolution
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Geologic Timescale
Red and blue areas indicate hot (Hot House) and
cold (Ice House) periods
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Geologic Time Scale Relative to One Year
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Major Human Events on a Relative Time Scale of
One Year
Starting time to present
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The Anthopocene Epoch

• The Anthopocene is a new Epoch characterized by
  human-caused major global changes that have
  altered the Earth in fundamental ways.
• It starts at the beginning of the Industrial
  Revolution in 1751.
• We are no longer in the Holocene.

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Mass Extinctions

• The K/T extinction was due to a large impact that
  radically changed the climate.
• The other extinctions appear to be due to natural
  climate changes.
• The greatest mass extinction (P/T) was due to a
  climate change from an Ice House to a Hot House.

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Causes of Climate Change

• Abundance of Greenhouse Gases
• Major Volcanic Eruptions
• Large Asteroid or Comet Impact
• Change in Suns Irradiance
• Change in Ocean Circulation
• Continental Drift
• Change in Earths Motions

Red main cause of current global warming
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Past Oxygen and CO2 Abundances
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Major Volcanic Eruptions

• Large volcanic eruptions can cool the climate for
  a few years by injecting ash into the
  stratosphere to reflect the Suns radiation back
  to space.
• Enormous eruptions over long periods can emit
  large amounts of CO2 to warm the climate.

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Large Asteroid or Comet Impacts

• Large impacts cool the climate by injecting dust
  into the stratosphere to reflect sunlight back to
  space.
• If the impact is in limestone a large impact will
  first cool the climate and then heat it up by
  releasing large amount of CO2 from the limestone.

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Changes in the Oceans Thermohaline Circulation
Can Change the Climate
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Continental Drift due to Plate Tectonics can
Change Climate over Millions of Years
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Changes in Earths Motions can Change the Climate
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Changes in the Suns Irradiance
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Soar irradiance through September 2008.
Reference Fröhlich, C. and J. Lean, Astron.
Astrophys. Rev., 12, pp. 273--320, 2004.
http//www.pmodwrc.ch/pmod.php?topictsi/composite
/SolarConstant
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Solar Irradiance, Temperature, and Atmospheric CO2
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Solar Irradiance, Temperature, and Human-Caused
CO2 Emissions
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Conclusions

• Only two causes can operate on time scales short
  enough to account for todays rapid warming 1)
  increase in solar irradiance, or 2) increase in
  greenhouse gases.
• The increase in solar irradiance is not enough to
  account for the present warming and its rapid
  rise.
• The increase in greenhouse gases must be the
  cause of global warming.
• This is consistent with the observed rapid rise
  in both greenhouse gases and their emission by
  humans.

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Generalized Climates for the Past 3 Billion Years
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Cenozoic Era
End of Cretaceous (65 My BP)
Present Day
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Climate Change During Past 180 Million Years
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The Paleocene-Eocene Thermal Maximum (PETM)
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The Pliocene/Pleistocene Ice House
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• Summary Cenozoic Era
• Dominant Forcing Natural CO2
• - The natural imbalance of CO2 between
  sources and sinks is about 0.0001 ppm/year or 100
  ppm/million years
• - Human-made rate today 2 ppm/year
• - It takes humans 1 year to emit what
  nature emits or absorbs in 20,000 years
• Humans Overwhelm Slow Geologic Changes
• 2. Climate Sensitivity High
• - Antarctic ice forms if CO2 lt 450 ppm
• - Ice sheet formation reversible
• Humans Could Produce A Different Planet

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Change in Sea Level During the Last Glacial and
Interglacial Periods
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Sea Level in North America if all Ice on Earth
Melted
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Extent of the Ice Sheet that Covered North
America during the Last Ice Age
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Temperature Variations During the Past 140,000
Years
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Abrupt Climate Change Our Worst Nightmare
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Variations in Temperature During part of the Last
Ice Age
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The Younger Dryas and Other Abrupt Climate
Changes
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Several Abrupt Climate Changes