Past Climates or Paleoclimatology

Estimated Phanerozoic Temperatures (14° is Today; 16° is Critical and 18° is Catastrophic for Humans)

Generalized Climates for the Past 3 Billion Years

Climate Change During Past 180 Million Years

Cenozoic Era End of Cretaceous (65 My BP)Present Day

The Paleocene-Eocene Thermal Maximum (PETM)

The Pliocene/Pleistocene “Ice House”

Summary: Cenozoic Era 1. Dominant Forcing: Natural Differences in CO 2 - Rate ~100 ppm/Million years ( 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 CO 2 < ~450 ppm - Ice sheet formation reversible Humans Could Produce “A Different Planet”

Change in Sea Level During the Last Glacial and Interglacial Periods

Sea Level in North America if all Ice on Earth Melted

Extent of the Ice Sheet that Covered North America during the Last Ice Age

Temperature Variations During the Past 140,000 Years

Abrupt Climate Change: Our Worst Nightmare

Variations in Temperature During part of the Last Ice Age

The Younger Dryas (YD) and Other Abrupt Climate Changes

Several Abrupt Climate Changes

Nine current tipping elements vulnerable to possible abrupt change. The time frames and threshold temperature increases may be modified with more data. RegionElement 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 YearUnknown Sahara and West African Monsoon Small changes to the monsoon have triggered abrupt wetting and drying on the Sahara in the past. 10 Years3-5° C Arctic Summer Sea-ice As sea ice melts it exposes darker ocean, which absorbs more heat than ice does, causing further warming. 10 Years0.2-4° C Amazon Rainforest Losing critical mass of the rainforest is likely to reduce internal hydrological cycling, triggering further dieback. 50 Years3-4° C Boreal Forests Longer growing seasons and dry periods increase vulnerability to fires and pests. 50 years3-5° C Atlantic Ocean Thermohaline Circulation Regional Ice melt will freshen North Atlantic water, shutting down the ocean circulation. 100 years3-5° C El Nino-Southern Oscillation (ENSO) Climate models suggest ENSO will enter a near- permanent switch-on raising temperatures. 100 years3-6° C Greenland Ice Sheet Break-up of ice sheet raising sea level drastically. 300 years1-2° C West Antarctic Ice Sheet Ice sheet is frozen to submarine mountains, so high potential for sudden release and collapse as oceans warm. 300 years3-5° C