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Fossil fuel combustion is basically
taking

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00:00:15,043 --> 00:00:19,100
a jolt from that battery of the biosphere.

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00:00:19,100 --> 00:00:21,680
We're digging up some buried organic
carbon, and

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00:00:21,680 --> 00:00:25,490
reacting with oxygen to get the energy
back.

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00:00:25,490 --> 00:00:28,200
One thing that may occur to you is,
Does that

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00:00:28,200 --> 00:00:31,420
mean we're going to use up the oxygen in
the atmosphere?

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00:00:31,420 --> 00:00:35,640
That would be like draining the battery
of a biosphere all the way dead.

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00:00:35,640 --> 00:00:40,730
Fortunately, for us, most of the buried
organic carbon in the earth is in an

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00:00:40,730 --> 00:00:47,120
inconvenient form to use as a fuel.
limestone rock is a big white thing.

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00:00:47,120 --> 00:00:52,790
But it has maybe a few tenths of a
percent of organic carbon, 

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00:00:52,790 --> 00:00:57,570
mixed in with it, in a form that we could never
extract, and put into a gas tank.

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00:00:57,570 --> 00:01:00,690
Most of the buried organic carbon is

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00:01:00,690 --> 00:01:03,700
not suitable as a fossil fuel.

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00:01:03,700 --> 00:01:07,950
There are three basic types of
fossil fuels.

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00:01:07,950 --> 00:01:12,320
And the most abundant of them, and
therefore the most important one for the

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00:01:12,320 --> 00:01:19,120
future of Earth's climate, is coal.
Coal is fossil

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00:01:19,120 --> 00:01:26,000
plant material that was protected from
being respired by, being deposited

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00:01:26,000 --> 00:01:30,580
in a swamp.
If you have a soil that has lots of

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00:01:30,580 --> 00:01:35,380
water, it's very waterlogged, it's hard
for oxygen from the air to get down in

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00:01:35,380 --> 00:01:40,940
there, so plant material, leaves,
roots,

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00:01:40,940 --> 00:01:46,120
or mosses, can accumulate as thick
deposits of

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00:01:46,120 --> 00:01:51,360
very pure organic carbon known as peat.
And then when that peat

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00:01:51,360 --> 00:01:57,350
is cooked, it it matures into what we call
coal.

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00:01:57,350 --> 00:02:00,090
There are two different types
of coal.

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00:02:01,430 --> 00:02:06,530
Coal that is formed in
salt-water conditions

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00:02:06,530 --> 00:02:09,620
tends to have more sulfur
in it,

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00:02:09,620 --> 00:02:13,370
because sea water has sulfur in the form
of sulfate.

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00:02:13,370 --> 00:02:16,420
Whereas, coal that's formed in fresh water
conditions tends to have

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00:02:16,420 --> 00:02:18,980
less sulfur in it.

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00:02:18,980 --> 00:02:21,840
You already know about the sulfate
aerosols.

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00:02:21,840 --> 00:02:23,810
This is where they come from.

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00:02:23,810 --> 00:02:26,770
When there is sulfur in the coal that's
released to the atmosphere,

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00:02:26,770 --> 00:02:30,570
it makes these little droplets, which
scatter light, change

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00:02:30,570 --> 00:02:33,865
the properties of clouds, the indirect
effect, and all that.

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00:02:34,760 --> 00:02:43,220
Coal is basically mostly elemental
carbon.

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00:02:43,220 --> 00:02:48,910
The oxidation state of carbon just by
itself is zero.

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00:02:48,910 --> 00:02:52,080
Coal is halfway between

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00:02:52,080 --> 00:02:55,140
the most oxidized form and the most
reduced form.

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00:02:55,140 --> 00:02:59,760
It only has half as much energy per
carbon as natural gas, which is the most

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00:02:59,760 --> 00:03:06,020
reduced form of carbon.
Coal is also not particularly convenient

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00:03:06,020 --> 00:03:10,080
as a fossil fuel, compared to the other
ones, because it's in a solid form.

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00:03:10,080 --> 00:03:16,930
And so, mostly what coal is used for is to
generate electricity

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00:03:16,930 --> 00:03:22,280
by burning it and using the heat to boil
water to make steam.

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00:03:22,280 --> 00:03:25,490
And then using the steam to drive the
turbine,

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00:03:25,490 --> 00:03:27,680
as opposed to oil which is in a nice
liquid

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00:03:27,680 --> 00:03:29,670
form that you can put in a gas tank.

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00:03:30,910 --> 00:03:34,300
Coal is the most abundant of the
fossil fuels.

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00:03:34,300 --> 00:03:38,620
Here are  approximate inventories
of different types of fossil fuels.

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00:03:38,620 --> 00:03:45,220
Rhese are somewhat fuzzy numbers
because how much coal we think can be

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00:03:45,220 --> 00:03:50,550
extracted from the Earth depends on how
far we're willing to go to

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00:03:50,550 --> 00:03:51,000
get it.

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00:03:51,000 --> 00:03:56,100
And on technological improvements in coal
mining, things like that.

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00:03:56,100 --> 00:03:59,844
But in general there's at least 10 times
more coal

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00:03:59,844 --> 00:04:04,069
or maybe 50 times more coal than the other
fossil fuels.

57
00:04:04,069 --> 00:04:09,202
The question of what Earth's climate
will look like in the year

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00:04:09,202 --> 00:04:14,293
2100 and beyond depends largely on what
happens to that coal.