Are humans intensifying the natural greenhouse effect?

The concentration of greenhouse gases in the atmosphere has been increasing ever since the beginning of industrialization at the end of the 18th century, so for more than 200 years. In the case of carbon dioxide, the main cause is the burning of carbon-based energy sources that have been created over the course of the Earth’s history (“fossil fuels”) – primarily coal, oil, and natural gas. When it comes to methane, the main sources include intensive agriculture practices (particularly livestock farming) and the use of fossil fuels (including leaks from natural gas wells and pipelines). Nitrous oxide, otherwise known as laughing gas, is also released mainly in agriculture (such as through the use of large amounts of artificial fertilizers).¹

At the same time, large areas of forest have been cut or burned down, bogs and wetlands have been drained, and land and soil use has changed, with no end to these developments in sight.  These changes are releasing further greenhouse gases, on the one hand, and mean there are fewer forests that can absorb and sequester carbon dioxide from the atmosphere, on the other hand.

In 2019, the annual average concentration of carbon dioxide in the Earth’s atmosphere was 411 ppm (parts per million molecules of dry air, measured at the Mauna Loa Observatory in Hawaii and representative of the Northern Hemisphere).² This marks an increase of almost 50 percent compared with the level before the onset of industrialization. As a result, the CO2 concentration is much higher than at any time in the past 800,000 years, and probably even higher than at any other point in the last three million years.³

Regarding methane, the annual mean of 1,866 ppb (parts per billion molecules of dry air, global average) in 2019 had already increased by a factor of roughly 2.5 compared to the preindustrial level.⁴ Because the greenhouse effect of methane per molecule is around 25 times greater than that of carbon dioxide, this increase also has a significant impact on the climate. The concentration of nitrous oxide (or laughing gas) in the atmosphere has increased from 270 ppb to more than 330 ppb since the beginning of industrialization.⁵

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