We evaluate the effects on CO2 production of replacement of coal with natural gas, increasing vehicle fuel economy, and doubling nuclear or renewable power.
First we introduce a simple accounting method or index for CO2 production. We take CO2 from a unit of natural gas energy as a reference 1. Then for the same energy from petroleum we take it as 1.4 CO2 since it produces 40% more CO2 than natural gas. For a unit of energy from coal we take 2 since it generates twice as much CO2 as natural gas. Renewables (including hydro) and nuclear power are taken as essentially zero in CO2 production.
The US energy sources by percent are shown in the graph below.
Here, petroleum is 36% of our energy, and multiplying by 1.4 gives 0.50 to the CO2 production index.
Natural gas is 27% of our energy, and multiplying by 1 gives 0.27 to the CO2 index.
Coal is 18% of our energy, and multiplying by 2 gives 0.36 to the CO2 index.
Renewables are 9% of our energy (mostly hydro) giving 0 CO2.
Nuclear is 8% of our energy giving 0 CO2.
The total index is 1.13. This is equivalent to 13% greater CO2 than if all our energy came from natural gas, and is a simple way to compare CO2 from various scenarios.
First lets evaluate what happens if natural gas replaces all coal production, which is in progress since natural gas is now cheaper. The 18% coal now adds 18% to natural gas, making the new natural gas 45% of our energy. Multiplying by 1 gives 0.45 to the CO2 index. The total CO2 index is now 0.45 plus the previous 0.50 from petroleum to give 0.95. The total CO2 production index has been reduced from 1.13 to 0.95, or a reduction of 16% to 84% of the present CO2 production.
Next, lets look at the added affect of increasing the fleet average fuel economy. Whereas the stated goal for 2025 is 55 mpg, there are exceptions to maintain the same types of models, and an estimate of 43 mpg has been given for the fleet average of new cars then. This will also probably need a fair percentage of hybrid vehicles. It will also take a decade for this to replace all cars. The average vehicle mileage today is 27 mpg. So the reduction in petroleum usage ratio wise is to 27/43 = 0.63 of present usage. Since present petroleum is 0.50 CO2 units, that will reduce it to 0.32 CO2 index. Adding that to the natural gas after replacing coal CO2 index of 0.45 gives a total CO2 index of 0.77. The ratio of 0.77 to the present 1.13 index is 0.68 or a reduction to 68% CO2 from the present.
This looks like the above present trend and goals will reduce CO2 by a third from the present.
A nuclear policy being considered a few years ago would have doubled nuclear energy in the US. Partly because of fear after Fukushima and due to costs, this is in doubt these days. But we consider it anyway to find out what its effect could be. At this point, we consider the extra 8% replacing the natural gas. The estimate is the same as if renewables were increased to cover the 8%. We reduce the natural gas from 0.45 by 0.08 to 0.37 for the CO2 index. Adding that to the future petroleum index of 0.32 gives a total index of 0.69. The ratio of that to the present index of 1.13 gives 61% of the present CO2 generation.
We see that without any real new energy source breakthroughs we can achieve a reduction to 61% of our present CO2 production by these conversions and fuel efficiency. The time scale here is only about 20 years or so.
We have assumed here that as our population grows there are no new energy demands. Electricity generation efficiency and industrial efficiency and household and lighting efficiencies have been working in our favor. With cheaper and better batteries, we can start to convert to electrical vehicles, which are also more efficient users of fuel that produces the energy.
In the world at large, there is hope in the large number of nuclear reactors being considered, and in the future conversion from Chinese coal to natural gas usage as well. We should do what we can to help future developing countries to adopt less smog and CO2 polluting sources than China has.
