In my last post I went over how much humanity impacts the carbon cycle, this post will outline where the carbon comes from.
The Human Release of Carbon
In my last post I outlined the carbon cycle and showed how much human output is compared to the amount that is removed in the cycle. This post will outline where that carbon is coming from.
This is is a bonus post. I have decided to outline where the CO2 is coming from as some people have been denying the numbers shown in my former posts.
Most of our electricity comes from the burning of fossil fuels, as much as 85%. Burning coal releases the most carbon dioxide, and it takes about 0.7 pounds (0.3kg) of coal per kilowatt hour of energy. Burning this coal releases about 2 pounds (0.9kg) of carbon dioxide. This is because coal is over 50% carbon.In the United States alone this amounts to about 1,364 million metric tons of CO2 per year. Natural gas is the second most used fuel (in the United States). Natural gas, which is mostly methane (CH4), releases half as much carbon per unit of energy as coal. In the United States 530 million metric tons of CO2 are released per year from natural gas.
*According to this government site, coal releases about 215.4 pounds of CO2 per million British Thermal Units (BTU). One million BTU equals 1,055,060,000 Joules. This may seem like a lot of energy but this is equal to 293 kilowatt hours. This means that coal releases 215/293 or 0.73 kg of CO2 per kilowatt hour. Coal releases on average about 0.44 kg of CO2 per 1 kilowatt hour. Source.
More than a kilogram of CO2 is released per kilogram of coal burned. The atomic mass of oxygen is 16 and the atomic mass of carbon is 12. This means CO2 is actually ~63% oxygen. That means the mass of CO2 can be somewhat misleading *
Most cars today run on petroleum. Petroleum releases about 8.89 kilograms of CO2 per gallon or 33.6 kilograms per liter. Moving large metal machines tends to take more energy than keeping your room lit. That means even though we use our cars less, it still leads to a massive amount of carbon being released into the atmosphere. This amounts to about 27% of the greenhouse gas emissions of the United States. Gasoline has about 9.15 kilograms of carbon per liter of gasoline. This ends up being over 1,700 million metric tons of CO2 being released in one year by the United States for transport alone. That makes sense considering the United states consumed 7.19 billion barrels of petroleum products in 2016 alone.
Each liter of gasoline about 8.65 kilowatt hours of energy. This translates to 11.7 kilowatt hours per kilogram, with some being lost to the inefficiencies of the motor. Each kilogram of gasoline creates about 3 kilograms of carbon dioxide. This is because gasoline is made out of hydrocarbons, which have 4 to 12 carbon atoms per molecule. As I outlined above, CO2 is mostly oxygen by mass and a little bit of carbon goes a long way.
The last major source of CO2 is industry, accounting for 21% of CO2 emission. (In other countries this is higher, because the US doesn’t really make anything.)The CO2 emissions from industry are divided into two groups, direct and indirect. Direct includes burning fuel for power or heat, chemical reactions, and some comes from leaks. Most goes to producing power, and about a third is lost to leaks. (The gulf spill is one example.) Indirect emissions come from the use of electricity and transportation by the company.
Most emissions come from on-site use, which accounts for 57% of emissions. The next greatest comes from natural gas emissions. Accidental natural gas emissions account for 13% of emissions. Another 7% of CO2 is released by using fossil fuels (or byproducts) for other uses. The rest is from chemical processes, like making steel, mining and processing coal, or making concrete.
Some people on Steemit claim that we overestimate the amount of carbon we release is an overestimate. This shows how we have measured what we do in detail.