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How Sensitive is the Climate?

How Sensitive is the Climate?. Tectonic Variations. Warm early Cretaceous (100 Myr). Royer et al, Nature (2007). Tectonic Variations. Models of relationship between carbon cycle and global temperature can be used to try to find best match with proxy temperature data. Tectonic Variations.

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How Sensitive is the Climate?

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  1. How Sensitive is the Climate?

  2. Tectonic Variations Warm early Cretaceous (100 Myr)

  3. Royer et al, Nature (2007) Tectonic Variations Models of relationship between carbon cycle and global temperature can be used to try to find best match with proxy temperature data

  4. Tectonic Variations Gives range of 1.5o to 6oC for warming associated with CO2 doubling

  5. Tectonic Variations

  6. Orbital Variations

  7. Orbital Variations EARTH-ORBITAL (‘MILKOVITCH’) CHANGES

  8. Antarctica Orbital Variations EARTH-ORBITAL (‘MILKOVITCH’) CHANGES A simple comparison of peak-to-peak changes gives an apparent sensitivity of greater than 10oC for warming associated with CO2 doubling What’s wrong with the reasoning?

  9. Estimated Temperatures in Antarctica The Last Glacial Maximum (“LGM”) A better approach:

  10. Suggests 2-3oC Tropical Cooling Estimated Temperatures in Antarctica Suggests 5-6oC Tropical Cooling The Last Glacial Maximum (21,000 Ka BP)

  11. The Last Glacial Maximum (21,000 Ka BP) Suggests 2-3oC Tropical Cooling Which is correct? Suggests 5-6oC Tropical Cooling Implications for Climate Sensitivity

  12. The Last Glacial Maximum (21,000 Ka BP) Suggests 2-3oC Tropical Cooling Suggests 5-6oC Tropical Cooling

  13. The Last Glacial Maximum (21,000 Ka BP) More recently, a large amount of proxy data have been merged (“PMIP-2”) giving a best estimate that global mean temperatures during the LGM were 3-5oC cooler than today Given the estimated ‘forcings’, these numbers imply a range of 2o to 4oC for warming associated with CO2 doubling

  14. Mid 1800s “Little Ice Age” Mid 1900s “Medieval Warm Period” Historical Variations

  15. Solar SOLAR OUTPUT VARIATIONS? 2000 1000 1200 1400 1600 1800 VOLCANOES Volcanism Historical Variations Over this timeframe, natural, ‘external’ forcing dominates until 19th century…

  16. Historical Variations Over this timeframe, natural, ‘external’ forcing dominates until 19th century…

  17. INDUSTRIAL AEROSOLS LAND USE CHANGE GREENHOUSE GAS CONCENTRATIONS Historical Variations Over this timeframe, natural, ‘external’ forcing dominates until 19th century… When anthropogenic influences begin to emerge…

  18. Industrial Aerosols Greenhouse Gases Modern Variations Over this timeframe, natural, ‘external’ forcing dominates until 19th century… When anthropogenic influences begin to emerge…

  19. Modern Variations

  20. Modern Variations

  21. Modern Variations Instrumental record alone implies sensitivity of around 3oC for 2xCo2 but since the record is so short, the estimate is very uncertain (could be anywhere from 1.5oC to 9oC) As we have seen however, a smaller upper limit on this range (of about 4-5oC) can be established based on other (paleoclimate) constraints

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