I recently spoke at a meeting about burning fossil fuels and how they release greenhouse gases that overheat the planet. When we got to audience questions, the last question turned out to be something that probably should have gone first: “What is a ‘fossil fuel’? And what are ‘greenhouse gases’?”

Sensible questions. The short answers are the fossil fuels are oil, natural gas, and coal, and the greenhouse gases are carbon dioxide, methane, nitrous oxide and fluorinated compounds. Well, there’s a mouthful. So what are they?

Fossil fuels

Oil

Oil is the largest source of U.S.-caused global overheating. Gasoline and diesel are refined from oil. When you fill up at a gas station, you are pumping a fossil fuel into your gas tank.

Your car runs by burning gasoline in your engine. When you burn gasoline, the burning creates water molecules and carbon dioxide.

If you drive a diesel truck, the same thing happens. Diesel burns into water and carbon dioxide that is released into the air.

That carbon dioxide is the stuff that got us into our global warming mess. Carbon dioxide is the biggest problem in greenhouse gases. For thousands of years, there were about two trillion tons of carbon dioxide in the air around the world. Since 1900, we added another trillion tons, increasing global carbon dioxide by 50%.

Jet fuel is refined from oil. Jet fuel contains the same kinds of molecules that burn into water and carbon dioxide; a flight to Hawaii releases carbon dioxide.

Propane is one of the chemicals that refineries get out of oil. When you light your camp stove, the propane burns into water and carbon dioxide. Propane stoves release the same carbon dioxide that is causing higher temperatures around the world.

Natural gas

Natural gas is the fossil fuel making the second-largest contribution to U.S. global heating. Natural gas molecules are very similar to petroleum oil molecules. Like oil molecules, they are made from carbon atoms and hydrogen atoms.

Most of the gas pumped into homes is methane. Methane burns like oil. Like oil, methane is made of carbon atoms and hydrogen atoms. As with gasoline, the hydrogens combine with oxygen to make water and the carbons combine with oxygen to make carbon dioxide.

Depending on the local gas utility, the gas pumped into your neighbors’ homes is between 67% and 97% methane. The rest of the pumped gas is mostly other gases (like propane) that burn into water and carbon dioxide.

When you light a gas stove, the flame starts releasing water vapor and carbon dioxide. (Natural gas also releases a variety of other pollutants. You need to have good ventilation for a gas stove.)

You may have seen advertising suggesting that natural gas “is the green energy,” and implying that natural gas doesn’t create greenhouse gases. Nope. The way ads can get away with saying that is, for a given amount of generated heat, natural gas releases less carbon dioxide. Not no carbon dioxide; just less.

For no carbon dioxide, you need existing solar panels, windmills, hydroelectric dams or nuclear power plants. Those are the “green energy” sources (although you might question whether radioactive waste from nuclear plants counts as “green”).

Coal

Coal used to be a bigger deal for global warming, but U.S. coal burning has dropped by more than half since 2007 as the U.S. switched from coal power plants to natural gas power plants. That’s a good thing. For a given amount of electricity, coal creates more global overheating pollution than gas.

Coal is mostly the same stuff as oil and gas. It is made of carbon atoms and hydrogen atoms. When a power plant burns coal, it makes carbon dioxide and water.

Coal also has a bunch of other stuff in it, so a power plant releases a bunch of other pollutants when it burns coal. As far as global warming is concerned, the big deal is that coal releases carbon dioxide.

Currently, in the U.S., coal burning creates about half as much carbon dioxide as gas or oil.

What are the greenhouse gases?

There are four greenhouse gases: carbon dioxide, methane, nitrous oxide and fluorinated compounds.

Carbon dioxide

Carbon dioxide is the big deal in greenhouse gases. Carbon dioxide produces 80% of the global heating from the U.S. Carbon dioxide stops infrared heat radiation that is headed to outer space and sends some of it back towards Earth.

Carbon dioxide is released when you drive a gasoline car or diesel truck, when you heat your home with natural gas, or when a power plant burns coal.

Methane

Methane causes 11% of the global heating pollution from the U.S. That is one seventh of the global heating of carbon dioxide.

The largest sources of methane in the U.S. are the oil, natural gas and coal industries. Methane leaks out of natural gas pipes and from coal mines and oil wells. That provides a nice side benefit: stop the fossil fuel industries and you stop a third of the methane releases.

Methane also comes from cattle gas and rotting sewage and landfills.

When someone wants to convince you of the importance of methane, they will point out that, if you have equal quantities of methane and carbon dioxide, the methane will produce about 28 times as much global warming.

That is true, but we release a lot less methane than carbon dioxide. If you have a choice of stopping methane or stopping carbon dioxide, please stop the carbon dioxide first. U.S. carbon dioxide causes seven times as much warming. Stop burning gasoline and natural gas, and you stop almost all U.S. global warming pollution.

Nitrous Oxide

Nitrous oxide causes 6% of the U.S. global heating pollution. U.S. carbon dioxide creates 13 times as much heating as nitrous oxide.

Nitrous oxide mostly comes from farms using older farming practices. We have innovations that will stop most nitrous oxide emissions.

Fluorinated compounds

The fourth greenhouse gas, fluorinated compounds, is actually a collection of gases. There are dozens of fluorinated compounds.

Fluorinated compounds are man-made chemicals used in machines that move heat, like refrigerators, air conditioners and heat pumps. Fluorinated compounds get released when they leak out of those machines. That is why you have to throw out refrigerators at specialized facilities that capture the gases.

Altogether, fluorinated compounds cause 3% of the global heating from U.S. greenhouse gases.

As with nitrous oxide, we already have solutions for replacing fluorinated compounds and stopping almost all their global heating.

That’s it

The fossil fuels are oil (and the products made from oil, like gasoline), natural gas (which is mostly methane), and coal. The greenhouse gases are carbon dioxide (80% of the problem), methane (11%), nitrous oxide (6%), and fluorinated compounds (3%).