What are greenhouse gases?

Greenhouse gases (GHGs) are the gases that absorb solar radiation reflected from the Earth’s surface and retain it in the atmosphere. The greenhouse effect is the process in which heat (infrared radiation) from reflected sunlight is trapped – without this, the Earth would be much colder than it is today.

GHG emissions, which are caused by human activities and the main driver of climate change, intensify the greenhouse effect. The Paris Agreement is a significant milestone in fighting climate change, as it is an international treaty that places legally binding targets for reducing emissions for all countries. The goal is to ideally limit global temperature increases to 1.5 °C above pre-industrial levels along with net zero emissions by 2050.

Types of greenhouse gases

Carbon dioxide (CO2)

Carbon dioxide makes up nearly three-quarters of global emissions. It lingers in the atmosphere for hundreds of years on average and is produced by burning fossil fuels and other organic matter. CO2 is emitted in nearly all economic sectors and industries and ‘carbon’ oftentimes becomes the shorthand for explaining many emissions terms, like carbon neutral and carbon footprint.

Because of its prevalence, CO2 is the standard by which the other GHG emissions are measured. Global warming potential (GWP) measures the emission energy of one tonne of gas relative to one tonne of CO2 over 100 years. The larger the GWP, the more it warms the Earth compared to CO2 over a given period. The mass measured from a gas using GWP provides a carbon dioxide equivalent (CO2e), which creates a standard to measure the impact of all atmospheric pollutants as well as calculate carbon footprints.

Methane (CH4)

Methane, the main constituent of natural gas, is released from landfills, natural gas and petroleum industries, and agriculture activities. It is much different from CO2 in that it lasts only about a decade in the atmosphere but has a GWP 28 times higher over a 100-year period. Methane makes up 21% of global GHGs.

Nitrous oxide (N2O)

Nitrous oxide, about 4.8% of GHG emissions, is 264 times more potent than CO2 over a 100-year period and survives a little over a century in the atmosphere. It mainly comes from agriculture and livestock as a fertiliser and when waste is put into landfill but is popularly known as laughing gas for its anaesthetic effects.

Fluorinated gases (F-gases)

Fluorinated gases are a group of gases that contain fluorine. These compounds have a GWP of up to tens of thousands of times greater than CO2 and have been regulated since the Montreal Protocol because of their depletion of the ozone layer. Although they are only 2.6% of GHG emissions, F-gases reside in the atmosphere for hundreds to thousands of years. They are primarily used as refrigerants, solvents, and in manufacturing.

Although water vapour is the most prevalent GHG, is not tracked the same way because it is continually fluctuating and too complicated to monitor. But increased water vapour is both a consequence and a cause of global warming, which is amplified by the other GHGs.

Where do GHGs come from?

Broken down into economic sectors, these are the activities that generate emissions worldwide (IPCC 2022):

  • Electricity and heat production (34%): burning fossil fuels for electricity and heat
  • Industry (24%): burning fossil fuels at industrial facilities for energy as well as emissions from transformation processes (chemical, mineral, etc.) and from waste management activities
  • Agriculture, forestry and other land use (22%): cultivating crops and livestock and deforestation
  • Transportation (15%): burning fossil fuels for road, rail, air, and marine transportation
  • Buildings (6%): energy produced onsite and burning fuels for heat and cooking
  • Therefore, these are the areas where reduction efforts should be prioritised.

Reducing GHGs through climate mitigation

The United Nations Environment Programme’s Emissions Gap Report (2023) calls for all countries, especially those with greater capacity and responsibility, to adopt ambitious sector-wide low-carbon development programs. Climate mitigation must be a mixture of different solutions.

An important step is to take steps towards decarbonisation: replacing fossil fuels with renewable energy across the board. Carbon sinks (trees, oceans, soil) absorb more carbon from the atmosphere than they release, so maintaining them provides a method for capturing emissions. Another is carbon capture and storage, which prevents emissions from entering the atmosphere at the source by storing them long-term in a geological formation.

For accountability, companies should follow the guidelines and principles set out by the Greenhouse Gas Protocol, which established a global framework to measure and manage emissions. They are notable for categorising emissions into three scopes:

  • Scope 1: a company’s direct GHG emissions
  • Scope 2: emissions from the production of electricity, heat, steam, and cooling purchased by a company
  • Scope 3: indirect emissions from a company’s activities from outside of its control, both upstream and downstream

You can learn more about measuring your company’s emissions and steps to reduce them with ClimatePartner Academy and Deep Dives.

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