Carbon dioxide emissions have been an area of great scrutiny in recent years. The issue of global warming has much to do with the heat-trapping emissions caused by many parts of industry. As such, options have been put forth to help reduce the amount of carbon emissions present in our world.
Innovations such as the electric were developed to steer people away from using gas powered, carbon emitting cars. Unfortunately, electric cars have yet to reach a point to where they are economically viable for every person. The cost to manufacture a true electric car to be as efficient as a gas powered car leads to a price well outside most income ranges. Cars like a Prius are not fully electric, but hybrid cars that run on both electricity and gas. While good options, they still have the issue of emitting carbon. Another issue with electric cars is that the electricity that powers them comes from power plants that easily produce more greenhouse gas emissions than a car ever will.
What is the solution then? Education, at least for now, on what greenhouse gas emission do to the world. Regulations on how industry deals with its waste. Technological advancement geared towards reducing carbon emissions by making machines more efficient. And eventually, perhaps producing viable, sustainable electric generation options to eliminate the need for fossil fuel based power system entirely.
For education purposes, the question above asks how much carbon is emitted per kilometer traveled in an average car. To simplify things a bit, we will amend the question to include greenhouse gas emission in general, not just carbon. This does not change the question much because, in terms of issues like global warming, greenhouse gases all have nearly the exact same effect. Thus, we can look at greenhouse gases in general, rather than just one.
The average car emits about 19 pounds of greenhouse gases per gallon of gas used. Multiply that by a few hundred million cars, trucks, and SUVs and it turns out cars are responsible for nearly 30% of all greenhouse gas emissions in the United States alone. It is roughly similar in other countries of similar technological stature. In third world countries, it is a bit less due to fewer amounts of cars and less technology in general.
The average car gets about 24.9 mpg (miles per gallon) in the United States as of 2017. This includes all cars, even fuel deficient cars like trucks and SUVs. Converting that to kilometers per liter gives 10.6 (rounded) km/L. That gives one part of the information necessary to answer the above question. The second part needed is the amount of greenhouse gases emitted per liter of fuel used.
In order to get that number, we need to know how many liters there are in gallon. The ratio is roughly 3.8 liters per gallon, or 0.26 gallons in a liter. If 19 pounds of greenhouse gases are emitted by the average car per gallon of gas used, then basic algebra gives us roughly 4.94 pounds of greenhouse gases emitted per liter of fuel. Dividing 10.6 km/L by 4.94 pounds of greenhouse gases gives 2.15 (rounded) pounds of gas per kilometer traveled in an average car. Multiply that by a couple hundred miles per tank and then again by a few hundred million cars and you have an obscene amount of greenhouse gases emitted by one country per day!