In 2012 human emissions of CO2 were 32,310 million metric tons.
In the same year we consumed 540 quadrillion BTUs (quads) of energy. However, about 61 quads of this was generated by renewable resources or nuclear power, so let’s say that burning 479 quads of energy created those 32,310 mmts of CO2.
At current levels of efficiency, that works out to about 73.8 million metric tons of CO2 for each quad.
Let’s imagine that we wanted to reduce emissions by 25% below our 1990 emissions, in line with the Kyoto Protocol. The world’s 1990 emissions were 22,261 mmts, less 25% gets us 16,700. Roughly 50% of what we emitted in 2012. How would we go about this?
Let’s see what we have to work with. According to the DOE EIA, this is the fuel portfolio the world used in 2012:
Liquids: 179.9 quads
Coal: 154 quads
Natural gas: 120.4 quads
Nuclear: 25.5 quads
Other: 60.6 quads
The ‘other’ category includes renewables–but also firewood and dung.
If we look at our goal using the portfolio approach we would say let’s convert coal to natural gas and nuclear. In addition, we would say let’s use clean energy to power trains and push to get everybody out of cars and planes and into trains (and metros).
If we were wildly successful–let’s say cutting liquids from 179.9 quads down to 90 and eliminating coal altogether (with half being replaced by natural gas and half by nuclear), we would save 14,000 mmts of CO2 from being emitted (the energy switch from coal to natural gas still produces emissions). And we would be almost there.
The sobering news is that to get an additional 75 quads from nuclear power we would have to construct about 600 new nuclear power plants… which we could do, of course.
But that immediately should start us thinking that a top down allocation of fuel portfolio choices may not be the best approach.
So we’ll look at alternatives in an upcoming post.