What are greenhouse gases?

Greenhouse gases (GHGs) are gases in Earth’s atmosphere that trap heat from the sunlight by preventing some of the heat from leaving the atmosphere. The primary greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. These gases lead to global temperature rise and subsequent environmental impacts, what we know as the climate crisis today.

Examples of major greenhouse gases

Here are some of the main greenhouse gases:

Carbon Dioxide (CO2)

There are two areas carbon dioxide can come from, natural and human-made sources. Carbon dioxide emit naturally from respiration by animals and plants, volcanic eruptions, wildfires, and the decay of organic matter. There are also the human-made sources, or anthropogenic sources, particularly through the burning of fossil fuels (coal, oil, natural gas) for energy and transportation, deforestation, and industrial processes.

Carbon dioxide is the most significant GHG from human activities, and its concentration in the atmosphere has been rapidly increasing since the industrial revolution.

Methane (CH4)

Human-made sources of methane include agriculture, landfills, coal mining, and oil and gas extraction. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide.

Nitrous Oxide (N2O)

Nitrous oxide are emitted from agricultural and industrial activities, as well as during the combustion of fossil fuels and solid waste. Nitrous oxide has a global warming potential 300 times greater than carbon dioxide. When inhaled in large amounts or without proper precautions, it can have adverse health effects, including neurological and mental effects.

Fluorinated Gases

Fluorinated gases include hydrofluorocarbons (HFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃), usually emitted from industrial processes, refrigeration systems, and a variety of consumer products.

Is water (H2O) is greenhouse gas?

Greenhouse gases trap heat from the sunlight, so by definition water/water vapor is a GHG. But we must be careful not to misconstrue its role.

Although water vapor is the most abundant greenhouse gas, it doesn’t drive changes in the greenhouse effect on its own. Instead, it acts as a feedback mechanism. What this means is that its effect is determined by other forces. As the atmosphere gets warmer due to other greenhouse gases, it can hold more water vapor. This amplifies the greenhouse effect of water vapor.

However, we must also note that water vapor doesn’t remain in the atmosphere for long. As a comparison, CO₂ can remain in the atmosphere for hundreds to thousands of years, whereas water vapor typically lasts just a few days before it condenses and falls as precipitation. Furthermore, human activities do not directly affect the concentration of water vapor in the atmosphere, but primarily through increasing temperatures resulting from other greenhouse gases.

What is Global Warming Potential?

Global Warming Potential (GWP) is a measure used to represent the comparative potency of GHGs in terms of how much heat they can trap in the atmosphere relative to CO2. Essentially, it’s a way of comparing the potential impact of different GHGs on global warming. For example, methane has a GWP of over 20 in a period of 100 years, meaning methane has about 25-30 times the warming potential of CO2 over 100 years. Nitrous Oxide has a GWP of approximately 298 times, and Hydrofluorocarbons (HFCs) can range from less than 1 to over 14,000.

What is Carbon Dioxide Equivalents?

Carbon dioxide equivalents (CO2e) is a metric similar to GWP, and is used to compare the emissions from various GHGs based on their potential to cause global warming. This measure standardizes the GWP of different gases to that of carbon dioxide.