greenhouse effect and global warming by eliwalker

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									Greenhouse Effect A simple model of global temperature
reflected solar radiation absorbed Earth reradiated

Energy incident ≡ SπR2 Energy reflected ≡ αSπR2 Energy re-radiated ≡ τ4πR2T4

S ≡ 1372 W/m2 α ≡ albedo = 0.31 τ ≡ 5.67 x 10-8 W/m2K4

Solve for T T = 255K (-18° C) Known T = +15° C, 33° C higher than model Why: Greenhouse Effect (Atmosphere transmits incoming radiation; absorbs outgoing radiation)

History Early atmosphere of earth ~1000 x more CO2 Enabled development of life 6 CO2 + 6 H2O C6H12O6 + 6 O2 (Other part of C cycle C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy)

What Atmospheric Gases Contribute to Greenhouse Effect?

CO2

Strong correlation between CO2 concentrations and ∆T. (Antarctic ice cores)

Recent History of Problem

From 1870 - 1990 From 1870 - 1990

CO2 content or atmosphere has increased 25% T has increased 0.5 - 0.7° C

Let’s calculate effect of CO2 increase in 1965 [CO2] = 320 ppm in 1990 [CO2] = 355 ppm Assume exponential growth C = C0ert 355 = 320er(1990-1965) r = 0.41% / yr If this rate continues, we can calculate time to double CO2 2 x 280 = 355e0.0041t pre IR value t = 110 yr Date = 1990 + 110 = 2100

Effect on T Doubling CO2

dinosaur era 1.5 - 4.5° C = ∆T

warmer than last 10,000 years Best model (NRC) ∆T = ∆Tdoub x ln CO2(t) ln 2 (CO2)0

Controversy is what this means for future Double CO2 ∆T ~ 1.5 - 4.5° C

Science O=C=O

CO2 motions (vib.)

Greenhouse gases

Global Carbon Cycle

Currently the cycle is out of balance. Humans release 6 -7 x 109 tons of C to atmosphere / yr. (5 x 109 tons due to fossil fuels. Effect: Deforestation ~ 1 - 2 x 109 tons)
1 x 109 ton 0.47 ppm CO2

of the 6 - 7 x 109 excess tons / yr ~ 3 x 109 tons goes into atmosphere (3 - 4 x 109 tons ocean + biosphere

Mathematics of Climate change In estimating the “greenhouse effect” we assumed that the energy absorbed by the earth was equal to the energy radiated. Suppose they are not. Qabs ≠ Qrad Suggest that Qabs + ∆Qabs + ∆F = Qrad + ∆Qrad

∆F = ∆Qabs - ∆Qrad ∆Ts = λ∆F climate sensitivity parameter Approx. Qrad (W/m2) = 1.83 Ts (°C) + 209 0.34 < λ < 1.03 λ av ~ 0.57

C emissions from fossil fuels

Syn fuels are terrible, coal is bad, nat. gas is better. However, as we said earlier, the biggest resource is coal.

Let’s make some models C emissions = Population x GNP x Energy x C emissions person GNP energy Assume exp. growth r = rpop + rGNP/pop + renergy/GNP + remissions/energy
1.8% 1.5% -0.8% -0.2%

Base case

(1.0)

(1.2)

US Policy April 21, 1993

US goal of return in 2000 to 1990 emission level is announced

Results to date:

Other greenhouse gases CFCs (Chlorofluorocarbons) Principal component of ozone problem, as well. Currently regulated by Montreal protocol that requires a 50% reduction (rel. to 1986) by 1998. BUT, because of long lifetime in atmosphere.

Methane (CH4) natural sources

decaying matter “bovine flatulence” termite farts 25 x more absorbing than CO2 ~1% / yr increase (correlated with population increase).

Belching and farting

N2O (nitrous oxide) fossil fuel burning fertilizer use + 0.2 % / yr Net Effect

Aerosols Provide “negative” forcing

Overall Net Effect

Connection with energy

Regional Effect of T increase

Profound effect on agriculture, water supply (no or reduced snowpack) ∆h (sea) ∆t + 10 - 20 cm 1900 - 2000 + 10 - 20 cm 2025 + 50 - 200 cm 2100 ~ 6m 2300


								
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