Scientists have been warning about global warming since at least 1912.

[DetlefK]

https://thinkprogress.org/headlines-back-in-1912-warned-coal-consumption-affecting-climate-b0c1373194a1/

As the full clipping read (emphasis added), “The furnaces of the world are now burning about 2,000,000,000 tons of coal a year. When this is burned, uniting with oxygen, it adds about 7,000,000,000 tons of carbon dioxide to the atmosphere yearly. This tends to make the air a more effective blanket for the earth and to raise its temperature. The effect may be considerable in a few centuries.”

The fact-checking website Snopes.com verified the authenticity of those clippings and traced the story to the caption in a lengthy article in the March 1912 issue of Popular Mechanics on “The effect of the combustion of coal on the climate — what scientists predict for the future.”

“It has been found that if the air contained more carbon dioxide, which is the product of the combustion of coal or vegetable material, the temperature would be somewhat higher,” the article explains. “Since burning coal produces carbon dioxide it may be inquired whether the enormous use of the fuel in modern times may not be an important factor in filling the atmosphere with this substance, and consequently indirectly raising the temperature of the earth.”

...

Indeed, the scientific understanding that certain gases trap heat and warm the planet dates back to the 1850s. Eunice Foote discovered CO2’s warming properties in 1856, and was the first scientist to make the connection between CO2 and climate change.

...

In a 1917 paper, Alexander Graham Bell wrote that the unrestricted burning of fossil fuels “would have a sort of greenhouse effect.”

Global warming works like this:

The Sun radiates a certain amount of heat onto Earth and Earth radiates a certain amount of heat back into space. The ratio determines how warm Earth is.

How good this infrared-radiation can leave Earth, that depends on the atmosphere. Gases like carbondioxide, water and methane are good scatterers for infrared radiation. That means, they are not transparent to it but tend to scatter it sideways in random directions. (Imagine the light of lamp scattered in a fog.)

If the atmosphere contains too much of these gases, that increases the odds that a photon of infrared radiation that normally would have left Earth will instead be scattered sideways and will remain in Earth's vicinity, increasing the odds that it will be absorbed by some matter and heat it.

Earth now receives the same amount of heat from the Sun as before, but the amount of heat leaving Earth has been reduced, and this new ratio means that Earth now has an average temperature higher than before.

[DBoon]

1. Since 1896

In developing a theory to explain the ice ages, Arrhenius, in 1896, was the first to use basic principles of physical chemistry to calculate estimates of the extent to which increases in atmospheric carbon dioxide (CO2) will increase Earth's surface temperature through the greenhouse effect.[3][20][21] These calculations led him to conclude that human-caused CO2 emissions, from fossil-fuel burning and other combustion processes, are large enough to cause global warming. This conclusion has been extensively tested, winning a place at the core of modern climate science.

https://en.wikipedia.org/wiki/Svante_Arrhenius