What are greenhouse gases?

Carbon dioxide is just one of the gases that contribute to global warming. Discover the list of seven other substances

Before listing what greenhouse gases (GHG) are, it is necessary to understand that the greenhouse effect it is a natural process, caused by the presence of a series of gases in the atmosphere and responsible for retaining part of the heat that reaches the Earth through solar radiation. Thanks to this greenhouse — and what is absorbed by the oceans and the Earth's surface —, we inhabit a planet where the temperature makes the survival of its species viable.

Because of the our activities here, the natural phenomenon that guarantees the survival of many species (among them ours, the human one) now puts their existence at risk.

As the concentration of GHGs in the atmosphere increases, the energy radiated from the surface becomes trapped and cannot leave the planet, being reabsorbed and forcing the Earth to seek a new thermal balance. This is why an excess of these gases is behind the rise in Earth's average temperature, also known as global warming, and climate change, the increase in intensity and frequency of extreme weather events, such as droughts, fires, hurricanes and floods. 

Governments, companies and society has, in some way, tried to take actions to change this panorama, either by signing agreements to control the emission of these gases, or by seeking technologies to reduce the release or capture of these gases from the atmosphere or simply adopting habits that are less harmful to the environment

O Kyoto Protocol, one of these international agreements that aim to reduce the emission of pollutants, in 1997 listed the following gases that should be controlled to avoid global warming and which, since then, have been known as greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) sulfur hexafluoride (SF6), hydrofluorocarbon (HFC), perfluorocarbon (PFC) and water vapor (H2O). In 2015, in a round of protocol updates, another gas was added: nitrogen trifluoride (NF3).

Carbon dioxide (CO2)

It is what contributes most to global warming and is therefore often used as a synonym for the expression “greenhouse gases”. It is also the gas that receives the most attention from emission reduction or sequestration of the atmosphere

The human contribution to the increase of this gas in the atmosphere is mainly due to the burning of fossil fuels (whether in transport, energy generation or for heating) and logging. According to the UNEP (United Nations Environment Programme), it can persist in the atmosphere for more than a thousand years.

Methane (CH4)

The main source of human emissions of this gas comes from agriculture, especially livestock (from manure and the animals' digestive tract). According to the UN body, 32% of the gas released by human action comes from there. Irrigated rice cultivation is another source of CH4 released into the atmosphere, approximately 8%. Oil and gas extraction, coal mining and landfills together represent 55% of emissions.

Methane is responsible for around 30% of global warming since pre-industrial times and, according to UNEP, is proliferating rapidly. This gas can remain in the atmosphere for a decade.

Nitrous oxide (N2O) 

Nitrous oxide was already in the atmosphere, just in small quantities. What humans did was increase their concentration through industrial activity, the burning of fossil fuels and agricultural practices – which are responsible for more than 2/3 of emissions. N2O can remain in nature for more than 100 years.

Sulfur Hexafluoride (SF6), Hydrofluorocarbon (HFC) and Perfluorocarbon (PFC)

They are also called fluorinated gases and are not produced naturally, like the other three already mentioned. HFC was the answer given by the industry to replace chlorofluorocarbon (CFC), banned from industrial production for destroying the ozone layer. The other gases, explains UNEP, have industrial and commercial uses.

water vapor

It is the most abundant GHG and contributes most to the greenhouse effect, but our contribution to this is almost irrelevant. Virtually all water vapor present in the atmosphere comes from natural processes.

Nitrogen trifluoride (NF3) 

Despite not being on the initial list of the Kyoto Protocol, nitrogen trifluoride was added to the list of greenhouse gases in 2015. One study published in 2008 in Nature classified NF3 as “a rare but extremely potent greenhouse gas.” According to the publication, it is 12 to 20 thousand times more efficient at retaining heat than CO2. Nitrogen trifluoride is commonly used in the manufacture of flat-screen TVs and monitors. Its useful life in the atmosphere is estimated at 740 years. 

Indirect greenhouse gases

In addition to the gases mentioned above, there is a list of indirect greenhouse gases, as shown in National Atmospheric Emissions Inventory, the UK government body responsible for calculating annual pollutant emissions in that country. 

These are gases that can indirectly increase the concentration of a substance in the atmosphere or contribute to its heating or cooling.

Are they: 

  • Nitrogen oxides (NOx)
  • Carbon monoxide (CO)
  • Non-methane volatile organic compounds (NMVOC)
  • Sulfur dioxide (SO2)

Brazil and its emissions

At the end of 2021, the Climate Observatory showed that Brazil increased its greenhouse gas emissions during the pandemic, contrary to the movement observed in the rest of the world. They grew 9.5% here while they reduced 7% in other countries.

O deforestation of the Amazon was the main cause for the increase in these emissions in a year in which the economy experienced a slowdown. Data SEEG (Greenhouse Gas Emission Estimation System), show that eight, of the ten municipalities that release the most GHGs into the atmosphere are from the North region of the country. The country's two largest urban centers, São Paulo and Rio de Janeiro, complete the list. 

With 3.2% of global emissions, Brazil is the fifth largest emitter of greenhouse gases in the world, behind China, the United States, Russia and India. In 2020, the average CO2 emission per Brazilian was 10.2 gross tons, against 6.7 for the world average. 

According to the report “Analysis of Brazilian emissions and their implications for Brazil’s climate goals 1970 – 2020”, in addition to deforestation (also called Land Use Change and Forestry), the following sectors of the economy contributed to the emission of more than 2.16 billion tons of CO2 equivalent into the atmosphere: agriculture, energy (includes transport), processes industrial and waste.

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