Fossil fuel combustion is basically taking
a jolt from that battery of the biosphere.
We're digging up some buried organic carbon, and
reacting with oxygen to get the energy back.
One thing that may occur to you is, Does that
mean we're going to use up the oxygen in the atmosphere?
That would be like draining the battery of a biosphere all the way dead.
Fortunately, for us, most of the buried organic carbon in the earth is in an
inconvenient form to use as a fuel. limestone rock is a big white thing.
But it has maybe a few tenths of a percent of organic carbon,
mixed in with it, in a form that we could never extract, and put into a gas tank.
Most of the buried organic carbon is
not suitable as a fossil fuel.
There are three basic types of fossil fuels.
And the most abundant of them, and therefore the most important one for the
future of Earth's climate, is coal. Coal is fossil
plant material that was protected from being respired by, being deposited
in a swamp. If you have a soil that has lots of
water, it's very waterlogged, it's hard for oxygen from the air to get down in
there, so plant material, leaves, roots,
or mosses, can accumulate as thick deposits of
very pure organic carbon known as peat. And then when that peat
is cooked, it it matures into what we call coal.
There are two different types of coal.
Coal that is formed in salt-water conditions
tends to have more sulfur in it,
because sea water has sulfur in the form of sulfate.
Whereas, coal that's formed in fresh water conditions tends to have
less sulfur in it.
You already know about the sulfate aerosols.
This is where they come from.
When there is sulfur in the coal that's released to the atmosphere,
it makes these little droplets, which scatter light, change
the properties of clouds, the indirect effect, and all that.
Coal is basically mostly elemental carbon.
The oxidation state of carbon just by itself is zero.
Coal is halfway between
the most oxidized form and the most reduced form.
It only has half as much energy per carbon as natural gas, which is the most
reduced form of carbon. Coal is also not particularly convenient
as a fossil fuel, compared to the other ones, because it's in a solid form.
And so, mostly what coal is used for is to generate electricity
by burning it and using the heat to boil water to make steam.
And then using the steam to drive the turbine,
as opposed to oil which is in a nice liquid
form that you can put in a gas tank.
Coal is the most abundant of the fossil fuels.
Here are approximate inventories of different types of fossil fuels.
Rhese are somewhat fuzzy numbers because how much coal we think can be
extracted from the Earth depends on how far we're willing to go to
get it.
And on technological improvements in coal mining, things like that.
But in general there's at least 10 times more coal
or maybe 50 times more coal than the other fossil fuels.
The question of what Earth's climate will look like in the year
2100 and beyond depends largely on what happens to that coal.