Carbon dioxide (CO2) is an important heat-trapping (greenhouse) gas, which is released through human activities such as deforestation and burning of fossil fuels, as well as natural processes such as respiration and volcanic eruptions.
Carbon dioxide concentrations are rising predominantly due to the burning of fossil fuels for various purposes; with the transportation, energy and industrial sectors being the three largest contributors. Fossil fuels include coal, petroleum, natural gas, oil shales, bitumens, tar sands, and heavy oils. All of these contain carbon and were formed as a result of geologic processes acting on the remains of organic matter (both plant and animal) over the span of many millions of years. Carbon dioxide levels today are higher than at any point in at least the past 800,000 years.
CO2 emissions from human activities have caused the concentration of carbon dioxide in the Earth’s atmosphere to go up from around 275 parts per million (ppm) before the industrial revolution to over 410 in 2020; a 50% increase!
The year 2020 was an exception. After rising steadily for decades, global carbon dioxide emissions fell by 6.4%, or 2.3 billion tons, due to the COVID-19 pandemic, which significantly contracted economic and social activities worldwide. Although the decline is significant (roughly double Japan’s yearly emissions), it is not expected to last once the virus is brought under control.
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