Carbon dioxide (CO₂) is a greenhouse gas (GHG) generated predominantly through the burning of fossil fuels. In the atmosphere, greenhouse gases absorb and re-emit thermal radiation that would otherwise escape into space. In proper concentrations, greenhouse gases help ensure the Earth remains at a habitable temperature—however, modern consumption of fossil fuels has resulted in excessive emissions of CO₂ and other greenhouse gases. This, in turn, has created a "greenhouse effect" in which too much heat is captured, which disrupts Earth's carbon cycle and accelerates global warming.
Global warming and climate change have severe ecological impacts, including extreme weather events (floods, blizzards, storms), drought, sea-level rise, and disturbed water systems. CO2 emissions are a major part of each country's overall greenhouse gas emissions, and also contribute to a country's total pollution levels. Global CO₂ emissions are tracked by agencies such as the European Union's Emissions Database for Global Atmospheric Research (EDGAR), which compiles data from several sources to generate comprehensive annual reports on CO₂ emissions around the world.
*For a full list of countries and their emissions, see the table at page bottom
China has the highest overall level of CO₂ emissions, producing 11.680 gigatons (11.68 billion tons, or 11,680 million tons) of CO₂ emissions in 2020, followed by the United States with 4.535 gigatons and India with 2.412 gigatons. However, it is worth noting that these are also the world's three most populous countries, so their high rank among emitters of CO₂—which is released predominantly though transportation networks and electricity production—can be credited in no small part to their higher overall populations.
This notion is reinforced when one balances the rankings by dividing total consumption by the country's population, resulting in a list of the world's highest CO₂ emitters per capita (per person). This method results in a notably different top ten list:
Between 2010 and 2019, total global CO₂ emissions increased from 33.1 gigatons to 38 gigatons, a number that is projected to increase in the coming years. In the United States, energy use has increased for the past six+ years, due to factors including increased electricity consumption due to increased use of heating and cooling systems and a rising level of travel and tourism than in previous years. This increase comes after almost a decade of declining energy use.
In general, developed countries have higher CO₂ emissions due to their more developed infrastructures—particularly their electrical power grids and road/transportation networks--and higher standards of living. However, as seen in the per-capita chart above, developing or emerging countries and countries with quickly growing economies often see their emissions rise as well as their infrastructure expands to serve their growing population.
Highly developed countries are also the best-positioned to develop and deploy more efficient technologies such as solar power and other renewable energy systems. Developed and technologically advanced countries such as Denmark, Luxembourg, and Switzerland are among the most environmentally friendly, implementing green initiatives to reduce their carbon footprint, lower CO₂ emissions and GHG emissions, and improve their overall environmental friendliness and health.
In addition to national initiatives, there are several methods that individuals can use to reduce their carbon footprint. These include eating less red meat (meat production releases both CO₂ and methane, another greenhouse gas); choosing to walk, bike, carpool, or use public transportation instead of driving; updating outdated appliances with more energy-efficient models; and using reusable shopping bags, bottles, and other containers instead of disposable packaging.
China emits the most CO2 globally. In 2020, it released 11,680.2 million tons (gigatons) of CO2. Palau had the highest emissions per capita, 55.29 million.