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Nitrous oxide levels

The recent role of the greenhouse effect

Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO2 and other heat-trapping gases to the atmosphere. These greenhouse gas emissionshave increased the greenhouse effect and caused Earth’s surface temperature to rise. The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from the burning of fossil fuels.

The main greenhouse gases

The most important GHGs directly emitted by humans include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and several others. The sources and recent trends of these gases are detailed below.

Carbon dioxide 

Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change. CO2 is absorbed and emitted naturally as part of the carbon cycle, through plant and animal respiration, volcanic eruptions, and ocean-atmosphere exchange. Human activities, such as the burning of fossil fuels and changes in land use, release large amounts of CO2, causing concentrations in the atmosphere to rise.

Atmospheric CO2 concentrations have increased by more than 40% since pre-industrial times, from approximately 280 parts per million by volume (ppmv) in the 18th century to over 400 ppmv in 2015. The monthly average concentration at Mauna Loa now exceeds 400 ppmv for the first time in human history. The current CO2 level is higher than it has been in at least 800,000 years.[2]

Some volcanic eruptions released large quantities of CO2 in the distant past. However, the U.S. Geological Survey (USGS) reports that human activities now emit more than 135 times as much CO2 as volcanoes each year.

Human activities currently release over 30 billion tons of CO2 into the atmosphere every year.[2] The resultant build-up of CO2 in the atmosphere is like a tub filling with water, where more water flows from the faucet than the drain can take away