The long-term fossil fuel
problem
Earth 497
Kasting
Questions:
• How much will atmospheric CO2 go up if
we burn all the fossil fuels?
• How long will it take to get back to
“normal” (the preindustrial state)
• To solve the long-term fossil fuel problem, one needs to keep track
of both DIC and alkalinity in the oceans
• The steady-state (preindustrial) values of these quantities are
determined by the carbonate-silicate cycle
The BLAG model
• Reservoir sizes are in units of 1018 moles
• Fluxes are in 1018 mole/m.y.
Weather rate correction factors
• Weathering rates depend on land area
• Weathering rates also depend on atmospheric CO2, via
the greenhouse effect and the temperature and rainfall
dependence of weather
Metamorphic (volcanic) correction
factor
• Rates of CO2 release
from volcanism are
assumed to be
linearly proportional to
seafloor spreading
rate
• Past spreading rates
can be estimates from
paleomagnetism (but
it is hard to do
accurately!)
BLAG model results
• Atmospheric CO2 was up to 100 times higher in the not-too-distant
past, according to some parameter estimates
• A more realistic estimate (the linear decrease model) gives a factor
of 6 enhancement in CO2 at 100 Ma
• We can take the BLAG chemistry, convert
the equations to sources and sinks for DIC
and Alk, and use them to estimate how
atmospheric CO2 might change in the
distant future
• To do this, we need to also convert from a
1-box ocean to (at least) a 2-box ocean, to
take into account the biological pump
“Simple” 3-box model for fossil fuel
CO2 uptake
• Atmosphere-ocean CO2
exchange is calculated using
piston velocity arguments
• Mixing between the surface and
deep ocean is estimated based
on tracer measurements (14C)
• Downward fluxes of organic and
carbonate carbon from the
surface ocean to the deep ocean
establish pH gradients within the
ocean
Atmosphere
Surface ocean
Forg
Fcarb
Deep ocean
Ocean carbon cycle results: pCO2
Ocean carbon cycle results: pCO2
Ocean carbon cycle results: pH
Ocean carbon cycle results:
Lysocline depth
Ocean carbon cycle results:
Airborne fraction