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
radiation; absorbs outgoing radiation)
Earth solar 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?
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.)
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