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  • Writer's pictureHeidi Harting-Rex

What are Greenhouse Gases?

Greenhouse gases (GHGs) are a mixture of certain global atmospheric pollutants. Many are products of using fossil fuels. Scientists use the term “greenhouse gases" because these emissions trap heat close to Earth’s surface, just like a greenhouse would, which is why it is also called the “greenhouse effect”. Since many of the gases are naturally occurring, Earth’s atmosphere has previously been able to absorb them and slowly release them in cycles that maintained a stable average temperature. However, the human impact on our planet now exceeds the atmosphere’s capacity to do this, like a bucket overflowing.

There are many greenhouse gases, and each affects the atmosphere differently. This is because some last longer and/or are more capable of trapping heat than others. Scientists often use the term “carbon dioxide equivalent” (CO2e) to standardize the impacts of each gas; this illustrates how much greenhouse effect each gas produces related to that of carbon dioxide(CO2). CO2 is one of the biggest players, but the other GHGs include water vapor, methane, nitrous oxide, hydrofluorocarbons (a common refrigerant), perfluorocarbons (from making aluminum and semiconductors), sulphur hexafluoride (from electricity transmission) and nitrogen trifluoride (from making TVs and microelectronics). We’ll talk about the three most common gases.

CO2 is the most prevalent; it is a natural chemical compound and we as humans breathe it out. Scientists started measuring CO2 levels in the 1950s. The levels have increased, consistently, every year since. The pre-industrial concentration of CO2 in the atmosphere was below 280 ppm (parts per million). We are presently over 420 ppm. We have more CO2 in our atmosphere now than in the last four million years. At that time, sea levels were 30-80 feet higher. Once CO2 is in the atmosphere, it remains for a long time, making an impact for several hundred years.

We humans emit over 30 billion tonnes of CO2 per year, or four megatons per person. That means an average person, weighing 150 pounds, puts his/her weight of CO2 into the atmosphere in one week

Carbon is necessary for life on earth. And the natural world, without human interference, is abundant in carbon sinks, or places that absorb it to maintain an equilibrium. We cause destruction in two ways simultaneously: by emitting and by eliminating sinks. The oceans, forests and other natural areas all absorb carbon. We’ve reached a tipping point in their capacity, however, as excess CO2 in the oceans causes higher temperatures, acidification and massive die offs, like coral reefs. 

Methane is next. It is responsible for about 17% of warming. It’s a byproduct of processing and transporting fossil fuels. Large industrialized cattle lots, rice fields, peat moss harvesting and rotting organic matter in landfills also release it. Since the Industrial Revolution, methane concentrations in the atmosphere have increased by 160%, the highest in 800,000 years. Methane lasts around twelve years in the atmosphere, yet is 25 times more potent than CO2.

The third gas is nitrous oxide. We release less of it, yet it is around 300 times stronger than CO2. In the last century, we’ve seen a 100% increase in the fixed nitrogen on earth, largely due to industrialized farming. Nitrous oxide lingers for around 100 years.

The hard part about GHGs is realizing that, even if we stop emitting tomorrow, the gases will not disappear from our atmosphere.

All images copyright John Moore (

Climate Change Q/A is produced by Heidi Harting-Rex, an avid climate change reader, and Rosie Ferguson, a graduate of the University of Montana Journalism School with a minor in Climate Change Studies.

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