Use of pollen data to investigate past climates: spatial and ecological sources of uncertainty
Past Climates or
description
Transcript of Past Climates or
Past Climatesor
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 Era1. 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 < ~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.
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-iceAs sea ice melts it exposes darker ocean, which absorbs more heat than ice does, causing further warming.
10 Years 0.2-4° C
Amazon RainforestLosing 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 SheetIce sheet is frozen to submarine mountains, so high potential for sudden release and collapse as oceans warm.
300 years 3-5° C