EARTH’S CLIMATE, THE GREENHOUSEEFFECT, AND ENERGY

---AN INTRODUCTION

Stephen E. Schwartz

College Mini-semester Program

January 7, 2008

http://www.ecd.bnl.gov/steve

GLOBAL ENERGY BALANCEGlobal and annual average energy fluxes in watts per square meter

Schwartz, 1996, modified from Ramanathan, 1987

ATMOSPHERICRADIATION

Energy per area pertime

Power per area

Unit:Watt per square meterW m-2

STEFAN - BOLTZMANN RADIATION LAWEmitted thermal radiative flux from a black body

F T= σ 4

F = Emitted flux, W m-2

T = Absolute temperature, K

σ = Stefan-Boltzmannconstant, W m-2 K-4

600

500

400

300

200

100

0

Em

itted

Infr

ared

Rad

iatio

n, W

m-2

-40 -20 0 20 40Temperature, °C

300280260240Temperature, °K

Top of Atmosphere

Global MeanSurface Temperature

Stefan-Boltzmann law “converts” temperature to radiative flux.

370360350340330320310

20001990198019701960

C. D. Keeling

Year

CO

2 co

ncen

trat

ion

(ppm

)

180

200

220

240

260

280

300

320

340

360

380

800 1000 1200 1400 1600 1800 2000

Law Dome Adelie LandSipleSouth Pole

Mauna Loa Hawaii

ATMOSPHERIC CARBON DIOXIDE IS INCREASING

Global carbon dioxide concentration and infrared radiative forcing over the last thousand years

Polar ice cores

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Forcing, W

m-2

RADIATIVE FORCING

A change in a radiative flux term in Earth’s radiationbudget, ∆F, W m-2.

Working hypothesis:On a global basis radiative forcings are additive andfungible.

• This hypothesis is fundamental to the radiativeforcing concept.

• This hypothesis underlies much of the assessment ofclimate change over the industrial period.

ATMOSPHERIC CARBON DIOXIDETime series 1700 - 2003

500

450

400

350

300

Car

bon

diox

ide

mix

ing

ratio

, ppm

2000195019001850180017501700

Law Dome (Antarctica) Siple (Antarctica)Mauna Loa (Hawaii)

Law - Etheridge et al.Siple - Friedli et al.

Mauna Loa - Keeling

ATMOSPHERIC CO2 EMISSIONSTime series 1700 - 2003

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Car

bon

diox

ide

emis

sion

s, p

pm/y

r

2000195019001850180017501700

6

5

4

3

2

1

0

Carbon dioxide em

issions, Pg C

/yr

Fossil Fuel Emissions

Fossil Fuel - Marland

ATMOSPHERIC CARBON DIOXIDETime series 1700 - 2003

500

450

400

350

300

Car

bon

diox

ide

mix

ing

ratio

, ppm

2000195019001850180017501700

Fossil Fuel Cumulative Emissions

Fossil Fuel - Marland

ATMOSPHERIC CARBON DIOXIDETime series 1700 - 2003

500

450

400

350

300

Car

bon

diox

ide

mix

ing

ratio

, ppm

2000195019001850180017501700

Fossil Fuel Cumulative Emissions

Law Dome (Antarctica) Siple (Antarctica)Mauna Loa (Hawaii)

Law - Etheridge et al.Siple - Friedli et al.

Mauna Loa - KeelingFossil Fuel - Marland

DEFORESTATION AS A SOURCE OFATMOSPHERIC CO2

ATMOSPHERIC CO2 EMISSIONSLand-use changes 1850 - 2000

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

Car

bon

diox

ide

emis

sion

s, p

pm/y

r

2000195019001850

2.5

2.0

1.5

1.0

0.5

0.0

Carbon dioxide em

issions, Pg C

/yr Total United States Canada Latin America Europe North Africa and Middle East Tropical Africa Former Soviet Union China Tropical Asia Pacific Developed Region

Houghton, Tellus, 1999; Houghton and Hackler, 2002

Carbon flux estimated as land area times carbon emissions associated withdeforestation (or uptake associated with afforestation).

United States dominates emissions before 1900 and uptake after 1940.

ATMOSPHERIC CO2 EMISSIONSTime series 1700 - 2003

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Car

bon

diox

ide

emis

sion

s, p

pm/y

r

2000195019001850180017501700

6

5

4

3

2

1

0

Carbon dioxide em

issions, Pg C

/yr

Land Use Emissions Fossil Fuel Emissions

Fossil Fuel - MarlandLand Use - Houghton

Prior to 1910 CO2 emissions from land use changes were dominant.

Subsequently fossil fuel CO2 has been dominant and rapidly increasing!

ATTRIBUTION OF INCREASE INATMOSPHERIC CO2

Comparison of cumulative CO2 emissions from fossil fuel combustion andland use changes with measured increases in atmospheric CO2.

500

450

400

350

300

Car

bon

diox

ide

mix

ing

ratio

, ppm

2000195019001850180017501700

400

300

200

100

0

Cum

ulative carbon dioxide emissions, P

g C

Fossil Fuel Cumulative Emissions

Fossil + Land UseCumulative Emissions

Land Use ChangeCumulative Emissions

Law Dome (Antarctica) - Etheridge et al Siple (Antarctica) - Law et alMauna Loa (Hawaii) - Keeling

Prior to 1970 the increase in atmospheric CO2 was dominated byemissions from land use changes, not fossil fuel combustion.

CLIMATE RESPONSEThe change in global and annual mean temperature,∆T, K, resulting from a given radiative forcing.

Working hypothesis:The change in global mean temperature isproportional to the forcing, but independent of itsnature and spatial distribution.

∆T = λ ∆F

CLIMATE SENSITIVITYThe change in global and annual mean temperature perunit forcing, λ, K/(W m-2),

λ = ∆T/∆F.

Climate sensitivity is not known and is the objective ofmuch current research on climate change.

Climate sensitivity is often expressed as thetemperature for doubled CO2 concentration ∆T2×.

∆T2× = λ ∆F2×

∆F2× ≈ 3.7 W m-2

CLIMATE SENSITIVITY ESTIMATESTHROUGH THE AGES

Estimates of central value and uncertainty range from majornational and international assessments

6

5

4

3

2

1

0

∆T2×

, Sen

sitiv

ity to

2 ×

CO

2, °C

190018901880

Arrhenius

Stefan-Boltzmann

2010200019901980

CharneyNRC – – – – IPCC – – – –

1 sigma> 66%

"Likely"

1.5

1.0

0.5

0.0

Sensitivity, K

/(W m

-2)

Despite extensive research, climate sensitivity remains highly uncertain.

THE ‘BIBLE’ OF CLIMATE CHANGEIt's big and thick.Every household should have one.No one reads it from cover to cover.You can open it up on any page

and find something interesting.It was written by a committee.It is full of internal contradictions.It deals with cataclysmic events such as

floods and droughts.It has its true believers and its rabid skeptics.

IMPLICATIONS OF UNCERTAINTY INCLIMATE SENSITIVITY

Uncertainty in climate sensitivity translates directlyinto . . .

• Uncertainty in the amount of incrementalatmospheric CO2 that would result in a givenincrease in global mean surface temperature.

• Uncertainty in the amount of fossil fuel carbon thatcan be combusted consonant with a given climateeffect.

At present this uncertainty is about a factor of 3.

IMPORTANCE OF KNOWLEDGE OFCLIMATE TO INFORMED

DECISION MAKING

• The lifetime of incremental atmospheric CO2 is about100 years.

• The expected life of a new coal-fired power plant is50 to 75 years.

Actions taken today will have long-lasting effects.

Early knowledge of climate sensitivity can result inhuge averted costs.

KEY APPROACHES TO DETERMININGCLIMATE SENSITIVITY

• Paleoclimate studies: Forcing and response over timescales from millennial to millions of years.

• Empirical: Forcing and response over the instrumentalrecord.

• Climate modeling: Understanding the processes thatcomprise Earth’s climate system and representing themin large-scale numerical models.

Climate models evaluated by comparison withobservations are essential to informed decision making.