Greenhouse gases will take you by surprise!

Published on April 18, 2024


1) Why is carbon dioxide (CO2) a greenhouse gas and oxygen (O2) is not? Is it because of the carbon?

Yes, but not only.

The presence of the carbon atom plays a fundamental role. Not because it’s carbon but because it’s combined with two oxygen atoms. The gas molecules determine if it is a greenhouse-gas. To absorb infrared rays, a gas must contain at least three atoms or two different atoms in its molecule.

That’s why CO2 is a greenhouse gas. It has one carbon atom and two oxygen atoms. Oxygen is not a greenhouse gas because it has two identical atoms.

2) Is the atmosphere composed primarily of greenhouse gases?

No, far from it!

Ninety-nine percent of our atmosphere is naturally made up of oxygen (O2), nitrogen (N2) and argon (Ar). These gases do not have greenhouse-effect characteristics.

Greenhouse gases account for only 1% of the atmosphere. When it comes to the greenhouse effect, it’s not majority rules!

3) Is CO2 the primary greenhouse gas?

The answer is... no!

The main greenhouse gas is - wait for it - water vapor. Seriously, water vapor! Water in all its forms, water vapor and clouds, is responsible for 75% of the greenhouse effect.

Why do we think CO2 when we hear global warming, and not water vapor?

Human activities have virtually no direct influence on the concentration of water vapor in the atmosphere. And consequently, no direct influence on its greenhouse effect.

4) Are greenhouse gases naturally present in the atmosphere?

Yes, in part.

Our atmosphere is naturally made up of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and water vapor (H2O). Human activity increases the concentrations of these gases and strengthens their greenhouse effect. Water vapor is the exception and the proportion generated by human activity is anecdotal.

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Proportion of greenhouse gases in the atmosphere without the impact of human activity

On the other hand, human activities also emit additional greenhouse gases. The main ones are halocarbons including CFCs.

These “industrial” greenhouse gases are used in:

5) Is CO2 the most important gas in global warming?

Yes and no.

It’s all semantics! Let's be specific.

Additional human-generated greenhouse effects are due primarily to CO2.

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However, CO2 is also the gas with the lowest global warming power (GWP). GWP corresponds to the gas’s “radiative forcing”, that is, the amount of radiation it intercepts and returns to the ground. The GWP is generally calculated over a 100-year period. Using CO2 as a reference, it’s then possible to compare different greenhouse gases.

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As Galileo would say, it’s all relative.

One thing is certain. Mechanically speaking, global warming is not reversible because the greenhouse gas effect has long-term warming power.

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