Simply put, gases that trap heat within the earth’s atmosphere are called Greenhouse Gases.
They are able to do this through a process called ‘greenhouse gas effect’. Without the 'greenhouse gas effect' the earth’s average temperature would have been a frigid -18°C, altering the course of evolution completely.
The most abundant natural greenhouse gases in our atmosphere are:
- Carbon Dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O), &
- Water vapour
The heat trapping ability of these greenhouse gases come from their unique ability to:
- let solar radiation pass through them, to reach the earth’s surface,
- absorb the infrared radiation emitted back by the earth’s surface,
- re-emit this absorbed infrared radiation back to earth’s surface.
Remarkably, greenhouse gases, which play a crucial role in our climate system, exist in the atmosphere in extremely small amounts— far less than one percent by volume !!
For context, the earth’s atmosphere is about 78.08% Nitrogen, 20.95% Oxygen, & 0.93% Argon (by volume the dry air).
A brew of 'trace gases' which also include 'greenhouse gases' - accounts for the remaining 0.04% approximately.
That’s all it takes—less than a percent, yet it drives a world of impact.
Over the last many two centuries, the concentration of greenhouse gases in our atmosphere has first-gradually-and-then-exponentially increased !!
This abnormally high concentration has in-turn amplified the amount of heat that the greenhouse gases able to trap within the earth’s surface at any given moment – setting up our planet onto a path of increasing global warming & climate destabilisation.
To understand the speed at which this has happened, consider the fact that the carbon dioxide concentration in our atmosphere has close to doubled since mid-eighteenth century at the onset of industrial revolution (from 277.60ppm, 1749 to 421.02ppm, 2023). It has been under the 300ppm mark for more than 10,000 years before this.
The atmospheric concentration of Methane and Nitrous Oxide follow a similar trend during the same 1750-2023 period.
Methane concentration has more than doubled (from 719.01ppb to 1919.24ppb) &
Nitrous Oxide concentration has increased by close to 20% (from 277 ppb to 336.57 ppb).
While the growing greenhouse gas concentrations were already beginning to trap more heat, our industrial era also brought forth new industrial gases with greenhouse gas properties. Take the example of Fluorinated gases (F-gases), the most common them being HFCs (or hydrofluorocarbons).
All greenhouse gases do not ‘trap heat’ & cause global warming to the same extent.
Some greenhouse gases are more effective at ‘trapping heat’ than others.
For the same weight and time period, in order of increasing ‘heat-trapping' ability (lowest to highest), the greenhouse gases are,
- Carbon Dioxide (CO2)
- Methane (CH4)
- Nitrous Oxide (N2O)
- F-Gases
It is also worth nothing, that the 'heat trapping' ability of the greenhouse gas in the atmosphere gradually changes with time.
To allow comparison of the global warming impacts of different greenhouse gases, a unit of measurement called Global Warming Potential (GWP) was developed.
It represents the amount of energy (simplified: radiation) that a gas is able to absorb in comparison to carbon dioxide.
GWP of different greenhouse gases is measured for the for the same weight of gas (1 tonnes) over an equal time period (20 years, 100 years etc), to allow apple-to-apple comparison.
By definition, carbon dioxide (CO2) is considered base & has a GWP of 1 regardless of the time period.
The graph here shows how the various greenhouse gases compare against each other.
Higher the GWP of a gas, greater is its ‘heat trapping’ capacity & greater is the extent to which it contributes to global warming.
For example, methane has a 100-year GWP value of 28. This which means that the global warming influence of 1 tonne of methane gas is 28 times higher than carbon dioxide – making it far deadlier than carbon dioxide from a climate change point of view.
You will also notice in the table above that the global warming influence of the same GHGs changes over time.
We use cookies to personalise your content, and provide a better experience. By using our platform and services, you agree to our use of cookies as described in our cookie policy.
