Greenhouse gases
Greenhouse gases (GHGs) are gases in the Earth’s atmosphere that trap heat, contributing to the greenhouse effect.
The main greenhouse gases include:
Carbon dioxide (CO2): This is the main man made gas. It accounts for the largest share of greenhouse gases in the atmosphere (about 76% as of 2024). This gas is generated through burning fossil fuels (coal, natural gas and oil ), solid waste, trees, and some chemical reactions such as cement production.
Methane (CH4): Methane is emitted during the production and transportation of fossil fuels. Methane is also emitted through agricultural practices such as rearing livestock and decay of organic waste in landfills. In Ireland, agricultural activities account for the majority of Methane (CH4) emissions (around 90%). This is due to heavy cattle and sheep production which release methane (CH4) as a result of microbes breaking down food in their stomachs and intestines.
Nitrogen oxide (N2O): Nitrous oxide is emitted during agricultural, land use, and industrial activities; combustion of fossil fuels and solid waste; as well as during treatment of wastewater. In Ireland, agriculture contributes almost 90% of total N2O emissions, mainly due to nitrogen fertiliser use and emissions from animal waste.
F-Gases: These are Chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. They are often used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.
The Industrial Revolution and the use of fossil fuels (coal, oil, and gases) have raised carbon dioxide and nitrous oxide levels, disrupting the natural balance. Deforestation, farming, fertilizers, gases, and plastic pollution have also worsened the greenhouse effect, causing global warming.
Different GHGs can have different effects on the Earth’s warming. The two key ways in which these gases differ from each other are their ability to absorb energy (their “radiative efficiency”), and how long they stay in the atmosphere (also known as their “lifetime”).
The Global Warming Potential (GWP) measures how much energy 1 ton of a gas absorbs over time relative to 1 ton of carbon dioxide (CO2). A higher GWP means the gas has a greater warming effect than CO2. Typically, GWP is calculated over 100 years. It helps us compare the impacts of different gases and identify emission reduction opportunities.
Carbon dioxide (CO2) has a GWP of 1, regardless of the time period, because it serves as the reference gas. Once released, CO2 stays in the atmosphere for thousands of years, causing long-term increases in its concentration and contributing to climate change over a very long period.
Methane (CH4) is estimated to have a GWP of 27-30 over 100 years. CH4 emitted today lasts about a decade on average, which is much less time than CO2. But CH4 also absorbs much more energy than CO2.
Nitrous Oxide (N2O) has a GWP 273 times that of CO2 for a 100-year timescale. N2O emitted today remains in the atmosphere for more than 100 years, on average.
The F-Gases are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO2. The GWPs for these gases can be in the thousands or tens of thousands.
As of 2020, the sectors that contributed the most to global emissions were Electricity and Heat at 15.18 billion tonnes, Transport at 7.29 billion tonnes and Manufacturing and construction at 6.22 billion tonnes (Ritchie et al., 2020).
In 2023, the majority of GHG emissions consisted of carbon dioxide (CO2) accounting for 73.7% of total emissions, while methane (CH4) contributed 18.9% of the total, Nitrous Oxide (N2O) 4.7% and F-gases 2.7% 1.
In the same year, the world’s largest GHG emitters were China(15,943,986.55 ktCO2/year), United States(5,960,804.38 ktCO2/year), India(4,133,554.36 ktCO2/year), Russia (2,672,039.44 ktCO2/year) and Brazil (1,300,168.87 ktCO2/year).
The continued accumulation of carbon dioxide and other greenhouse gases in the atmosphere will cause a significant increase in global temperatures and disruptions to weather patterns worldwide. Rising temperatures will melt polar ice caps and low-lying areas will be flooded due to rising sea levels. Changing rainfall and snow patterns will cause widespread drought, particularly in important agricultural regions. The shortage of food and water will lead to major displacements of populations and civil unrest. Extreme weather events will become more common and lead to frequent extensive damage to property and significant loss of life (Hindricks and Myles, 2013).
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