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

anthropogenicincrease inCO2 and CH4

2000: 365 ppm

1800: 280 ppm

1. EnhancedGreenhouse Effect

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

280 ppm

560 ppm

GCM resultsfor CO2 sensitivity

Much variation.

Intergovernmental Panel onClimate Change (IPCC, 2007):+2.5 oC for 2 x CO2

560 ppm280 ppm

Q: Why is there so much uncertainty

in determining CO2 sensitivity?

Q: Why is there so much uncertainty

in determining CO2 sensitivity?

A: Because of feedbacks.

T - water vaporfeedback

T - albedofeedback

less snow & ice,lower albedo

more absorptionof radiationby ground

Some feedbacks to CO2 changes.

GCM resultsfor CO2 sensitivity

Curves steeper

Curves less steep

Why?

Q: Can’t we determine CO2 sensitivity

by using recent known temperature and

CO2 changes?

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

SO2 pollutionand sulfate

Global sulfate emissions

Temperature variationscorrelated with SO2 pollution?

1950-2000

x xx

x = major sulfate aerosol sourcesAverage: +0.7 oC/100 yrs

Thoughtexperimentillustratingdifferentresponse timesfor CO2 and SO2

Q: Can’t we determine CO2 sensitivity

by using past climate info?

Q: Can’t we determine CO2 sensitivity

by using past climate info?

A: Yes, to some extent.

CO2 data: ice coresT data: various

CO2 data: vegetation changesT data: various

b

a

a

b

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?

max

max

x

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?

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

CO2 only

5. What about other gases?

sulfur dioxide SO2

methane CH4

concentrations of both will probably go up

Melting ofmethane clathrateice in deep ocean& in permafrost

CH4

6. Projected temperature increase

What should happen on Earth as

temperature increases?

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

Assumes mid-range CO2 sensitivity:+2.5 oC for 2 x CO2

+5 oC for 4 x CO2

130 yrs

300 yrs

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?

IPCC (2007) sea level: +30 cm2 x CO2

in year 2100

Change in seasonsat mid-latitudes

2 x CO2

scenario atpeak warming

More changeat high latitudes(>40 o)especially inwinter(why?)

Sea level: +1 to 2 m4 x CO2

Yr 2200-2300

Sea level: +1 to 2 m

Bye-bye ice sheets? How quickly to melt?

“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