how sensitive is the climate?
Post on 13-Jan-2016
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How Sensitive is the Climate?
Tectonic Variations
Warm early Cretaceous (100 Myr)
Tectonic Variations
Models of relationship between carbon cycle and global temperature can be used to try to find best match with proxy temperature data
Royer et al, Nature (2007)
Tectonic Variations
Gives range of 1.5o to 6oC for warming associated with CO2 doubling
Tectonic Variations
Orbital Variations
EARTH-ORBITAL (‘MILKOVITCH’) CHANGES
Orbital Variations
EARTH-ORBITAL (‘MILKOVITCH’) CHANGES
Orbital Variations
Antarctica
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?
A better approach:
Estimated Temperatures in Antarctica
The Last Glacial Maximum (“LGM”)
Estimated Temperatures in Antarctica
The Last Glacial Maximum (21,000 Ka BP)
Suggests 2-3oC Tropical Cooling
Suggests 5-6oC Tropical Cooling
The Last Glacial Maximum (21,000 Ka BP)
Suggests 2-3oC Tropical Cooling
Suggests 5-6oC Tropical CoolingImplications for Climate
Sensitivity
Which is correct?
The Last Glacial Maximum (21,000 Ka BP)
Suggests 2-3oC Tropical Cooling
Suggests 5-6oC Tropical Cooling
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
Historical Variations
“Medieval Warm Period”
“Little Ice Age”
Mid 1800s
Mid 1900s
Historical Variations
VOLCANOES
SOLAR OUTPUT VARIATIONS?
Over this timeframe, natural, ‘external’ forcing dominates until 19th century…
1000
1200
1400
1600
1800
2000
Volcanism
Solar
Historical Variations
Over this timeframe, natural, ‘external’ forcing dominates until 19th century…
Historical Variations
GREENHOUSE GAS CONCENTRATIONS
INDUSTRIAL AEROSOLS
LAND USE CHANGE
Over this timeframe, natural, ‘external’ forcing dominates until 19th century…
When anthropogenic influences begin to emerge…
Modern Variations
Over this timeframe, natural, ‘external’ forcing dominates until 19th century…
When anthropogenic influences begin to emerge…
Greenhouse Gases
Industrial Aerosols
Modern Variations
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
Modern Variations
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