A greenhouse gas (GHG) is a gas that traps heat in the atmosphere. Greenhouse gases let sunlight pass through the atmosphere but prevent heat from leaving the atmosphere, also known as the greenhouse effect. Greenhouse gases are essential to keeping the Earth warm; without them, the Earth would be an average of about 0°F.
The primary greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.
Carbon dioxide is emitted through the burning of fossil fuels (coal, natural gas, oil), solid waste, biological materials, and as a result of some chemical reactions. Methane enters the atmosphere during the production and transportation of coal, natural gas, and oil and as a result of livestock and agricultural practices. Nitrous oxide is emitted during industrial and agricultural activities, the combustion of fossil fuels, and through the treatment of wastewater.
Of these, carbon dioxide (CO2) is the most abundant greenhouse gas. Since 1970, global carbon dioxide emissions have increased by 90%, with emissions from fossil fuel combustion and industrial processes contributing to about 78% of the total greenhouse gas emissions increase.
According to the Environmental Protection Agency (EPA), the economic sectors that produce the largest amounts of greenhouse gas emissions are electricity and heat production (25%), agriculture, forestry, and other land use (24%), industry (21%), and transportation (14%).
Emissions by Country
The world’s countries produce varying amounts of greenhouse gases into the atmosphere. The overall emissions level in a country can be explained by the size of its population, its GDP, its energy mix, and more.
In 2017, global carbon dioxide emissions from fuel combustion reached 32.8 billion tons in 2017 according to the International Energy Agency. China, the largest contributor, was responsible for 28% of these emissions, followed by the United States (14%), the European Union as a whole (10%), India (7%), Russia (5%), Japan (3%), Korea (2%), Canada (2%), Indonesia (2%), and Iran (2%). All other countries produced about 25% of emissions.
The 20 countries with the highest carbon dioxide emissions (in million tons (Mt)) are:
- China (9,300 Mt)
- The United States (4,800 Mt)
- India (2,200 Mt)
- Russia (1,500 Mt)
- Japan (1,100 Mt)
- Germany (718.8 Mt)
- Korea (600 Mt)
- Iran (567.1 Mt)
- Canada (547.8 Mt)
- Saudi Arabia (532.2 Mt)
- Indonesia (496.4 Mt)
- Mexico (446.0 Mt)
- Brazil (427.6 Mt)
- South Africa (421.7 Mt)
- Australia (384.6 Mt)
- Turkey (378.6 Mt)
- United Kingdom (358.7 Mt)
- Italy (321.5 Mt)
- France (306.1 Mt)
- Poland (305.8 Mt)
China has the highest greenhouse gas emissions of any country in the world. In 2017, China emitted 9.3 billion tons of carbon dioxide. China faces widespread criticism from the international community about its carbon footprint and is pressured to control its growing emission levels. The country’s economic growth has primarily been powered by coal, which produces up to twice the amount of carbon dioxide than other fossil fuels. China’s industrial sector is the primary coal consumer. Manufacturing, agriculture, mining, and construction make up about 62.5% of China’s energy use and 49% of its coal use.
2. The United States
The United States is the second-largest contributor of CO2 emissions, responsible for 4.8 billion tons of CO2 in 2017. The United States emitted a total of 6.5 billion tons of greenhouse gases. U.S. net emissions decreased by 12% between 2005 and 2017 with the electric power sector emissions falling 27% as a result of increased use of renewable energy, shifting from coal to natural gas, and leveling of electricity demand. The transportation sector is the largest contributor to emissions, responsible for 29% of emissions, followed by electricity (28%), and industry (22%).
India, like China, has a large population – the second-largest in the world of 1.38 billion people. India is the third-largest contributor of carbon dioxide emissions, emitting 2.2 billion tons of CO2 in 2017. Cattle, coal power plants, and rice paddies are the country’s major sources of emissions, which continue to rise rapidly. The country has pledged a 33-35% reduction in its emissions by 2030 compared to 2005 levels.
Russia is the fourth-largest contributor of CO2 emissions, emitting 1.5 billion tons of carbon dioxide in 2017. Russia’s per capita emissions are among the highest in the world: 53% higher than China and 79% higher than the European Union. The majority of greenhouse gas emissions in Russia are from the energy industry (78.9%), nearly half of which comes from the production of electricity and heat for the general population. Industrial production accounts for an additional 10.8% of total greenhouse gas emissions.
Japan is the fifth-largest contributor of greenhouse gases and the fifth and final nations that contributes over one billion metric tons per year. Japan emitted 1.1 billion tons of carbon dioxide in 2017. Japan is the only G7 country still building new coal-fired power plants. Japan has some unambitious climate change goals and is facing both criticism and pressure from the international community.
Germany is responsible for 718.8 million tons of carbon dioxide emitted in 2017. In 2019, Germany emitted 6.3% fewer greenhouse gases than in 2018. Since 1990, Germany has reduced its emissions by 35.7%. This is attributed to shutting down coal-fired power plants, expanding wind and solar energy, and successful reform of European emissions trading. Germany’s goal is to cut emissions by 55% by 2030 and to run on 80% renewable energy sources by 2050.
7. South Korea
Korea emitted 600 million tons of carbon dioxide in 2017. Korea emitted 709.1 million tons total of greenhouse gases, the highest it has ever been. The growth is attributed to an increase in gas emissions from electricity and heat production, specifically coal, and steel production. The number of new coal power plants that went into operation in 2017 surpassed the number that were decommissioned, leading to the major increase in greenhouse gas emissions.
Iran is the eighth-largest emitter of greenhouse gases in the world, emitting 567.1 million tons of CO2 in 2017. Between 1990 and 2016, Iran’s CO2 emissions rose by about 5% annually. The burning of natural gas and oil are the two leading contributors to Iran’s carbon emissions. Iran is rich in resources with enormous oil and gas reserves; however, it still has considerable renewable energy potential. Iran has pledged to reduce carbon emissions by 4% by 2030, but increased sanctions and a lack of trade have negatively impacted the country’s economy, preventing resources to be used for climate initiatives.
Canada emitted 547.8 million tons of carbon dioxide in 2017. Canada is warming up at twice the rate as the rest of the world, despite having a large network of hydroelectric dams and nuclear plants. Oil and gas production is Canada’s largest emitting sector, accounting for about 45% of emissions, followed by transportation, which accounts for about 28% of emissions. Despite Canada’s economy and population both growing since 1990, overall total greenhouse gas emissions per GDP and per person have declined.
10. Saudi Arabia
Saudi Arabia is the tenth-largest emitter of greenhouse gases, emitting 532.2 million tons of CO2 in 2017. Saudi Arabia’s economy is very oil-dependent and the country needs to diversify its economy and set higher goals in order to lower future emissions. Saudi Aramco, the official Saudi Arabian Oil Company, has contributed the most to global carbon dioxide emissions since the 1960s.