Carbon Dioxide's invisibility is what causes global warming

Australia's leader of the opposition Tony Abbott recently derided an emission trading scheme as "so-called market in the non-delivery of an invisible substance to no one". This echoes an earlier statement where Abbott dismissed carbon dioxide as an "invisible, odourless, weightless, tasteless substance". In this modern age, most people are aware of how something that is invisible to the eye can nevertheless have a significant impact. Examples include radiation from radioactive material, germs and well, gravity. In the case of carbon dioxide, it is actually its invisibility that is the key factor in how it causes global warming.

When sunlight reaches the Earth, it passes through our atmosphere. Greenhouse gases such as carbon dioxide are invisible to sunlight, also known as shortwave radiation because of its short wavelength. This allows the sunlight to pass through the atmosphere unhindered by greenhouse gases, and warm the Earth's surface.

The warm surface of the Earth radiates infrared heat, also known as longwave radiation because of its long wavelength. Greenhouse gases absorb longwave radiation. This results in the atmosphere trapping some of the Earth's heat as it tries to escape out to space. Heat-trapping gases such as carbon dioxide make the atmosphere warmer than it would be without any greenhouse gases.

Currently, we are adding greenhouse gases to the atmosphere through the burning of fossil fuels. As more greenhouse gases accumulate in the atmosphere, more heat is being trapped. This causes global warming. Consequently, the fact that carbon dioxide lets sunlight pass freely through the atmosphere is an integral aspect of the greenhouse effect. Carbon dioxide's invisibility is a key part of what causes global warming.

Greenhouse warming has distinct fingerprints that have been observed throughout our climate. As greenhouse gases trap more heat, satellites should measure less heat escaping out to space. This has been observed by a number of different satellites. Surface measurements observe more heat returning back to Earth.

Over 150 years ago, John Tyndall predicted the specific patterns of greenhouse warming - nights warming faster than days and winters warming faster than summers. Both these patterns have been observed. Another distinctive pattern of human-caused global warming is a cooling upper atmosphere at the same time that the lower atmosphere warms. This has also been observed.

Our confidence that humans are causing global warming is based on many, independent lines of evidence. Human fingerprints are being observed all over our climate.

Posted by John Cook on Tuesday, 16 July, 2013

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