The term “greenhouse gas” refers to any type of gas that has heat-trapping qualities when released into the atmosphere. Any number of substances can act as greenhouse gases, but the primary ones wherein humans are concerned are carbon dioxide and methane.

Primary Greenhouse Gasses

Carbon Dioxide (CO2)
Carbon dioxide is the most abundant type of greenhouse gas, making up around 0.037 of the volume of the troposphere and climbing with every particle of CO2 released. (Miller, 20114, p. 82) The concentration of CO2 in the troposphere today is higher than it’s ever been in the last 420,000 years. (Miller, 2004, p. 284)

CO2 is emitted by burning any type of carbon-based fuel, whether that be oil, coal, or plain old wood. So it’s released by any number of things, everything from cars to power plants to factories and forest fires.

Carbon remains in the atmosphere for anywhere from many decades to several centuries, and its warming effects can persist for a thousand years or more as a result of residual patterns set into motion. So we’re going to be dealing with the effects of the carbon released today for some time to come. Even if we halted all emissions today, temperatures would continue to rise and then stay elevated for many centuries because of this.

Methane
Methane is released as a waste product by organic life. Therefore everything from microbes to cattle emit this greenhouse gas. It is also buried in stores deep underground, the remnants of organic matter long since gone. It can bubble up through the ground, be released by melting permafrost, or be emitted as a result of mining activities.

Methane is the main component of natural gas, and currently oil and gas production is the main methane emitter. Cattle and livestock ranches also feature prominently in the equation, which is one of the reasons why diets heavy on meat are worse for the planet than plant-based diets. A California study found landfills were actually the biggest source of methane emissions, accounting for roughly 41% of methane emissions detected by remote sensing. This was followed by dairy farms and the oil and gas industry, each contributing around 26%. (Gremling, 2019)

Methane is much less prevalent in the atmosphere. While there are around 410 molecules of carbon dioxide for every million molecules of air, methane accounts for just 2 or so out of a million. (Jackson & Canadell, 2019) But those 2 per million can have a dramatic effect on climate change.

Methane is less worrisome in some ways and more worrisome in others. On one hand, methane has a much shorter atmospheric lifespan, so it doesn’t have the same millennia-spanning consequences that carbon does. On the other hand, it’s far more potent as a greenhouse gas, and so each molecule of methane has a more dramatic impact on warming trends.

“The good news about methane is that it remains in the atmosphere for a far shorter time than CO2 does,” write climate scientists Rob Jackson and Pep Canadell. “The bad news is that methane is vastly more efficient at trapping heat–more than 80 +times+ more, in the first 20 years after its release–which makes it, pound for pound, a bigger problem than carbon.” (Jackson & Canadell, 2019)

Methane is responsible for around a quarter of all current warming. (Krupp, 10-16-2018)

Water Vapor
Water vapor in the atmosphere also has a greenhouse effect, but because this has always been a part of our natural climate cycles, it’s typically ignored in climate science. The amount of water vapor released by human activities pales in comparison to what the earth produces on its own. That said, if higher temperatures lead to higher rates of evaporation, water vapor could become part of the feedback loop that makes climate change worse.

Other Types of Greenhouse Gases
There are many other types of gases that contribute to the greenhouse effect:

Black carbon
Mainly a byproduct of incomplete combustion in coal burning, diesel, and forest fires, this may be responsible for as much as 15-30% of the warming over the past 50 years.

Nitrous oxide
This gas is released as a byproduct of fertilizers, fossil fuel burning, nylon production, and livestock waste. It has around 296 times the heat-trapping potential of carbon dioxide. Rice paddies and inorganic fertilizers are a major source of this gas.

Chlorofluorocarbons (CFCs)
Used in air conditioners, refrigerators, and plastic foams, these have anywhere from 900 to 8,300 times the warming potential of CO2. Yet more concerning is the fact that they also destroy the ozone layer.

Hydro chlorofluorocarbons (HCFCs)
Meant to replace chlorofluorocarbons, which are being phased out, these have 470-2,000 times the warming potential of CO2.

Hydro fluorocarbons
Another gas used in air conditioners, refrigerators, and plastic foams, introduced to replace CFCs, with anywhere from 130 to 12,700 times the warming potential of carbon dioxide.

Halons
Released by fire extinguishers, these have 5,500 times the warming potential of carbon dioxide.

Carbon tetrachloride
A cleaning solvent that has 1,400 times the warming potential of carbon dioxide.

These other chemicals may have much more potent greenhouse effects, but because they are released in such comparatively small quantities compared to methane and CO2, they play a much smaller role in climate change. Still, they’re part of the overall equation.

Composition of the Atmosphere
Currently the composition of the atmosphere is as follows:

• Nitrogen: 78%
• Oxygen: 21%
• Water vapor: 0.01% at the poles to as much as 4% in the tropics around the equator
• Argon: slightly less than 1%
• Carbon dioxide: 0.037%
• + Trace amounts of other gases.