# Greenhouse Effect A simple model of global Effect A simple model of global temperature Energy incident ≡ SπR2 S ≡ 1372 W/m2 Energy reflected ≡ αSπR2 α ≡ albedo = 0.31 Energy

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• Greenhouse Effect A simple model of global temperature Energy incident SR2 S 1372 W/m2 Energy reflected SR2 albedo = 0.31 Energy re-radiated 4R2T4 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

absorbed

• 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?

CO 2 Strong correlation between CO2 concentrations and T. (Antarctic ice cores)

• Recent History of Problem

From 1870 - 1990 CO2 content or atmosphere has increased 25% From 1870 - 1990 T has increased 0.5 - 0.7 C

• Lets calculate effect of CO 2 increase in 1965 [CO2] = 320 ppm in 1990 [CO2] = 355 ppm Assume exponential growth C = C0e

rt 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 dinosaur era Doubling CO2 1.5 - 4.5 C = T warmer than last 10,000 years Best model (NRC) T = T doub x ln CO 2(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.)

Green-house 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. Deforestation ~ 1 - 2 x 109 tons) 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

Effect: 1 x 109 ton 0.47 ppm CO2

• F = Qabs - Qrad Ts = F climate sensitivity parameter Approx. Qrad (W/m

2) = 1.83 Ts (C) + 209 0.34 < < 1.03 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.

• Lets 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 (CH 4) natural sources decaying matter bovine flatulence termite farts 25 x more absorbing than CO2 ~1% / yr increase (correlated with population increase).

Belching and farting

• N 2O (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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