The release of certain gases into the Earth’s atmosphere can create a “greenhouse effect,” where heat is trapped and global temperatures rise. Although emissions can occur due to natural causes, they are primarily caused by human activities, especially the burning of fossil fuels for energy and transportation.
What are greenhouse gases?
When sunlight hits Earth, it produces heat. Consider the difference in temperature on a sunny day versus a cloudy day. However, when greenhouse gases (GHGs) are released into Earth’s atmosphere, they can create an insulating layer that prevents that heat from escaping back into space. Much like how a greenhouse creates a warmer environment for the plants it houses, these greenhouse gases trap heat in our atmosphere.
This greenhouse effect is vital; without it, the planet would be too cold to support life. However, since the Industrial Revolution, human activity has significantly increased the amount of greenhouse gas emissions in our atmosphere. By persisting for years or even centuries, they amplify the greenhouse effect and cause global temperatures to rise, making greenhouse gas emissions a major cause of global climate change.
What are the main types of greenhouse gases?
Experts consider carbon dioxide (CO2) to be the main driver of the greenhouse effect, but it is not the only contributor. The impact of other greenhouse gases, including methane (CH4), nitrous oxide (N2O) and fluoride gases such as chlorofluorocarbons, is measured in terms of carbon dioxide equivalent (CO2e). Measuring CO2e helps show the overall impact of all greenhouse gases, not just CO2.
The impact of each type of greenhouse gas is collectively measured in terms of its global warming potential (GWP). This metric compares the heat-trapping ability of the gas to that of CO2 over a specified period—for example, over 20, 100, or 500 years. For example, the 100-year GWP of CH4 is about 28–36 times that of CO2.
Carbon dioxide
The most abundant greenhouse gas, CO2 emissions account for three-quarters of all human-caused greenhouse gas emissions. The primary source of CO2 emissions is the burning of fossil fuels such as coal, oil, and natural gas for energy and transportation. CO2 is also released through deforestation and other land-use changes. Before the Industrial Revolution, global CO2 concentrations were around 280 parts per million (ppm). In May 2023, according to the National Oceanic and Atmospheric Administration’s Global Monitoring Laboratory, CO2 concentrations reached a record 424 ppm.1
Methane
CH4, the main component of natural gas, is less abundant than CO2 but more than 25 times more effective at trapping heat in the atmosphere. This is largely due to agricultural practices and livestock emissions (a single cow emits 220 pounds of CH4 each year2). However, animals aren’t the only source: CH4 emissions also occur when organic waste decomposes in landfills, and through rice harvesting practices, wetland habitats, and fossil fuel production and transportation.
Nitrous oxide
N2O comes from agricultural activities, industrial processes and the burning of fossil fuels. It is less abundant than CO2 and CH4 but is still a major contributor to global warming. Agricultural practices, particularly the use of synthetic fertilizers, are a major source of N2O emissions.
Fluorinated gases
Man-made synthetic gases—including hydrofluorocarbons, perfluorocarbons, chlorofluorocarbons, sulfur hexafluoride and nitrogen trifluoride—are used in processes such as refrigeration, air conditioning and electronics manufacturing. Although less common than CO2, CH4 and N2O, fluorinated gases are among the most effective at trapping heat and have the potential to persist in the atmosphere for thousands of years.
Where do greenhouse gas emissions come from?
Total greenhouse gas emissions come from several sources. Some are produced by natural processes; for example, volcanic eruptions and forest fires release CO2 and other gases into the atmosphere, while the decomposition of plants and animals releases CH4. However, the vast majority of global greenhouse gas emissions come from anthropogenic sources, meaning they are produced by human activities, such as:
Burning fossil fuels
Three-quarters of human-generated GHG emissions come from the burning of fossil fuels, including coal, oil, and natural gas. When they are burned to produce energy or as transportation fuels, they release large amounts of CO2 into the atmosphere. For example, cars and other vehicles that run on gasoline and diesel emit CO2 when the fuel is burned in their engines. Airplanes are a big contributor: burning jet fuel emits CO2 and other greenhouse gases at high altitudes, where they have a stronger impact on the atmosphere. Many power plants use coal, oil, or natural gas to generate electricity, as do heating and cooling systems for homes and buildings.
Agriculture
Livestock, especially cattle, produce CH4 during digestion, which is then released into the atmosphere. When large numbers of livestock are raised for meat production, the collective CH4 emissions can be enormous. Rice fields also emit CH4 during cultivation. When rice fields are flooded, this creates anaerobic conditions for bacteria to feed on the decaying natural materials, releasing CH4 in the process.
Deforestation
Forests are important carbon sinks, meaning they pull CO2 out of the atmosphere. When forests are cut down or burned, the trees release the carbon they stored. Demand for agricultural products often drives deforestation, which leads to land being cleared for crops and livestock.
Industrial processes
Certain manufacturing processes release GHGs. When raw materials are heated to high temperatures, they can produce CO2; for example, CO2 is a byproduct of the chemical reaction that converts limestone into clinker when producing cement. In the chemical manufacturing industry, the production of synthetic chemicals, plastics, and other products can produce CH4, N2O, and CO2.
Why are greenhouse gas emissions become a problem?
Greenhouse gases are necessary to maintain habitable temperatures on Earth. However, as greenhouse gas concentrations increase, they trap more heat in the atmosphere and the consequences for the global climate and environment become more severe. These consequences include:
Global warming
GHG emissions are a major contributor to global warming. They increase the greenhouse effect, which causes global temperatures to rise. The past few years have been among the warmest on record. According to the UN Intergovernmental Panel on Climate Change’s assessment report, each of the past four decades has been warmer than any previous decade since 1850.3 This increased heat can lead to more frequent and severe weather events such as hurricanes, floods, heat waves, and droughts.
Rising sea levels
Warmer temperatures are helping to accelerate the melting of polar ice and glaciers. This is contributing to rising sea levels, posing a major threat to coastal communities and low-lying areas.
Ocean acidification
More CO2 in the atmosphere leads to higher levels of CO2 in the world’s oceans. This causes ocean acidification, which can harm marine life, including coral reefs and shellfish.
Climate change can lead to a loss of biodiversity as species struggle to adapt to the changes or face extinction. Rising temperatures can affect bird migration patterns or lead to the introduction of invasive species. These changes can wreak havoc on the complex food chains that drive ecosystems, impacting every level.
Poor air quality
Some GHGs contribute to poor air quality, which can cause respiratory and other health problems in humans. Weather conditions caused by climate change, such as droughts and wildfires, can lead to increased levels of ground-level ozone, dust, smoke and other pollutants. They can also cause the spread or increase of allergens in the air.
Economic impact
Environmental disruptions can be detrimental to a range of industries and businesses by affecting supply chains and access to resources. Climate change can have a devastating impact on the agricultural sector, as extreme weather, changes in temperature and water access, and poor air quality can disrupt crop growth and harvests. Tourism and other weather-dependent industries are at risk; for example, ski resorts may close as warming temperatures reduce snow accumulation.
What helps reduce greenhouse gas emissions?
Because of their significant contribution to global warming, reducing greenhouse gas emissions is key to mitigating climate change. To achieve this, individuals, businesses and government agencies are joining forces in their efforts to lower emissions, aiming for the ultimate goal of net zero, the point at which the amount of greenhouse gases emitted equals the amount removed from the atmosphere, effectively bringing human-caused emissions as close to zero as possible. Strategies that can help reduce greenhouse gas emissions include:
Renewable energy
One of the most effective ways to reduce CO2 emissions is to switch from fossil fuels to renewable energy sources such as solar, wind and hydropower. This shift to renewable energy sources reduces reliance on the combustion of high-emission fossil fuels, thereby reducing emissions from power generation and transportation.
Energy efficiency
Improving energy efficiency in homes, buildings, and industrial spaces will reduce energy consumption and, as a result, greenhouse gas emissions. These changes in energy use can be achieved through building insulation, energy-efficient equipment, and sustainable design practices. At the corporate and industrial level, new technologies that enable better energy management can help companies reduce their carbon footprint.
Sustainable transport
Reducing emissions from the transport sector involves switching to electric vehicles, improving public transport, and encouraging carpooling, cycling and walking.
Sustainable agriculture and forestry
Implementing sustainable practices, such as reducing fertilizer use and responsible land management, can reduce N2O emissions and improve soil health. Restoring and planting trees can help pull CO2 from the atmosphere.
New technologies
Digitalization, artificial intelligence (AI), advanced data capture and analysis, and other technological innovations can contribute to reduction efforts. For example, the use of drones and sensors can help make agricultural and industrial processes more precise, ensuring the most efficient use of resources. Or AI-powered sorting systems can separate recyclables more accurately than manual sorting, aiding waste management practices.
Individual action
On a smaller scale, individuals take steps to reduce their personal carbon footprint. This includes recycling, switching to sustainable sources of energy and transportation, and other dietary and lifestyle changes. People can use tools such as the U.S. Environmental Protection Agency’s Household Carbon Footprint calculator4 or the United Nations Framework Convention on Climate Change’s Climate Change Lifestyle calculator5 to measure their impact.