Past%20Climates%20or

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Past Climatesor

• Paleoclimatology

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Estimated Phanerozoic Temperatures(14 is Today
16 is Critical and 18 is Catastrophic for
Humans)
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Generalized Climates for the Past 3 Billion Years
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Climate Change During Past 180 Million Years
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Cenozoic Era
End of Cretaceous (65 My BP)
Present Day
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The Paleocene-Eocene Thermal Maximum (PETM)
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(No Transcript)
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The Pliocene/Pleistocene Ice House
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• Summary Cenozoic Era
• 1. Dominant Forcing Natural Differences in CO2
• - Rate 100 ppm/Million years (0.0001 ppm/year)
• - Human-made rate today 2 ppm/year (20,000
  times faster than the natural rate)
• 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 (YD) and Other Abrupt Climate
Changes
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Several Abrupt Climate Changes
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Nine current tipping elements vulnerable to
possible abrupt change. The time frames and
threshold temperature increases may be modified
with more data.
Region Element Possible Time-frame Temperature Increase
Indian Summer Monsoon The regional atmospheric brown cloud is one of the many climate change-related factors that could disrupt the monsoon. One Year Unknown
Sahara and West African Monsoon Small changes to the monsoon have triggered abrupt wetting and drying on the Sahara in the past. 10 Years 3-5 C
Arctic Summer Sea-ice As sea ice melts it exposes darker ocean, which absorbs more heat than ice does, causing further warming. 10 Years 0.2-4 C
Amazon Rainforest Losing critical mass of the rainforest is likely to reduce internal hydrological cycling, triggering further dieback. 50 Years 3-4 C
Boreal Forests Longer growing seasons and dry periods increase vulnerability to fires and pests. 50 years 3-5 C
Atlantic Ocean Thermohaline Circulation Regional Ice melt will freshen North Atlantic water, shutting down the ocean circulation. 100 years 3-5 C
El Nino-Southern Oscillation (ENSO) Climate models suggest ENSO will enter a near-permanent switch-on raising temperatures. 100 years 3-6 C
Greenland Ice Sheet Break-up of ice sheet raising sea level drastically. 300 years 1-2 C
West Antarctic Ice Sheet Ice sheet is frozen to submarine mountains, so high potential for sudden release and collapse as oceans warm. 300 years 3-5 C