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Future climate (Ch. 19)
1. Enhanced Greenhouse Effect
2. CO2 sensitivity
3. Projected CO2 emissions
4. Projected CO2 atmosphere concentrations
5. What about other gases?6. Projected T increases
What will happen to Earth’s
climate system as the abundance
of greenhouse gases in the
atmosphere continue to increase?
What we need to know is Earth’s
“CO2 sensitivity”
2. CO2 sensitivity
T changes caused by changing CO2
abundance by given amount
CO2 sens. = (T change) / (change in CO2 amount)
e.g., for 2 x CO2 amount, 4 x CO2 amount
CO2 sensitivity
CO2 sens. = (T change) / (change in CO2 amount)
or
T change = (CO2 sens.) x (change in CO2 amount)
For given CO2 change:
If sensitivity high, T change large
If sensitivity low, T change small
Equivalent CO2
a measure of the amount of the combined effect
of all greenhouse gases, calculated as if CO2 were
the only greenhouse gas
GCM resultsfor CO2 sensitivity
Much variation.
Intergovernmental Panel onClimate Change (IPCC, 2007):+2.5 oC for 2 x CO2
560 ppm280 ppm
Q: Can’t we determine CO2 sensitivity
by using recent known temperature and
CO2 changes?
A: Yes, but…
We have to consider that response lags
behind forcing
And consider SO2 pollution
SO2 + 2H2O = H2SO4 + 2H
• SO2 released from burning, e.g. S-bearing coal
• This SO2 combines with water to make
sulfuric acid• Get cooling effect & acid rain
Effect of SO2 pollution
gas liquid liquid in solution
Produces cooling effect in atmosphere--what book calls “sulfate” aerosol
Temperature variationscorrelated with SO2 pollution?
1950-2000
x xx
x = major sulfate aerosol sourcesAverage: +0.7 oC/100 yrs
3. Projected CO2 emissions
% increase = % increase change change in
in C in x in emission x efficiency of
emissions population per person of C use
Projected CO2 emissions
% increase = % increase change change in
in C in x in emission x efficiency of
emissions population per person of C use
Likely to get higher or lower?
Projected CO2 emissions
% increase = % increase % change % change in
in C in x in emission x efficiency of
emissions population per person of C use
Likely to get higher or lower?
Projected CO2 emissions
% increase = % increase % change % change in
in C in x in emission x efficiency of
emissions population per person of C use
Likely to get higher or lower?
• Standard of living?• C taxes? Cap & trade?• Conservation?
Projected CO2 emissions
% increase = % increase % change % change in
in C in x in emission x efficiency of
emissions population per person of C use
Likely to get higher or lower?
Projected CO2 emissions
% increase = % increase % change % change in
in C in x in emission x efficiency of
emissions population per person of C use
Likely to get higher or lower?
• Fuel type (oil, gas, bituminous coal,
anthracitic coal, oil shale? H??)• Technology• Wind? Solar? Nuclear? Biofuels?
Current trends
minimum
(from pre-industrialCO2 value = 280 ppm)
Q: Why do curvesreach maximum?A: We run out offossil fuels
4. Projected CO2 atmosphere concentration
How does Earth redistribute CO2?
• Some stays in atmosphere• Some goes into biomass• Some into oceans
(over millions of years: into rock)
Roughly half of atmospherevalue
5. What about other gases?
sulfur dioxide SO2
methane CH4
concentrations of both will probably go up
What should happen on Earth as
temperature increases?
• More evaporation, more rain overall (exceptions!)• Cloudier• Less glaciers, sea ice, icesheets• More forests at high latitudes• More plant growth• Higher sealevel• Changes in habitat• Change in season length
4 x CO2 path (likely)could lead in 50-500to Earth like it was10-50 Myr ago
But… differentnow in rate at whichsystem changing
Use past as guide to the future?
“Estimated future changes in climate will beon a scale comparable to the largest naturalchanges of the past… We are now ~0.7 oC ofthe way [out of 2.5-5 oC projected warming]into this huge new experiment in transformingour planet…
Unless technology or extreme conservationefforts intervene, Earth is headed toward awarmer future at rates that are unprecedentedin its 4.5-billion-year history”
--Ruddiman, p. 357