The future of fossil fuels can be projected
with some amount of reason, by
extrapolating from what is going on today
and how we think things might change into the future.
There are lots of different ways that you can
do this scenario forecasting, some of them
very complicated, that take into account the individual countries
and individual situations, but you can also get there
from a broader perspective using this
formula, which is known as the Kaya identity.
The rate of carbon emission can be calculated as the product of
the population as you expect it to grow in the future, times the GDP per capita,
because fossil fuel use is so
closely tied with economic activity.
If we look at the units that we're building up here, population is people.
GDP per capita is dollars per person, per year.
And so the units of people cancels out there.
The third term is the energy intensity.
This is basically how much energy
it takes to make a dollar, to do a dollar's
worth of economic activity.
And this depends on whether you're making a dollar's worth of
steel or a dollars worth of coffee or something like that.
It makes a difference.
It also depends on on energy efficiency.
Now we've got watts per year.
and last term is has to do with this energy source,
how you're making the energy, the amount of carbon per watt of energy.
Nuclear power would have less carbon per watt than coal production.
The units now cancel, so we have watts or,
gigatons of carbon per year.
Extrapolating the present day trends
in these terms, we need to guess how high
we think earth's population is going to reach.
Hopefully it will plateau and stop growing, it looks like it's doing that.
The average income on the earth is increasing a function of time.
We can put the rate of change of that into the equation.
The energy use is getting more efficient.
The energy intensity is decreasing through time.
And then there are also changes in the carbon source that have to do with
efficiency, but also there's been a recent trend away
from coal because of lower prices for natural gases brought about
by improvements in the ability to extract natural gas known as fracking.
But you put all these things together, and you end up with
the projection that under business as usual, that means with no effort to
avoid climate change, the rate of carbon emission, today about 10 gigatons a
year, could grow to about 20 gigatons a year by the year 2100.