One hundred and fifty years ago, the brilliant Irish physicist John Tyndall published a paper in Philosophical Transactions of the Royal Society that helped to prove the existence of the greenhouse effect and its important influence on climate. Only for the 25 years or so have his discoveries been controversial, thanks to a steady pushback motivated by politics and financial interests. Tough break, science.
Nevertheless, in celebration of Tyndall and his work, the Royal Irish Academy and the Environmental Protection Agency have convened a conference in Dublin for Sept. 28-30. Richard Black of the BBC has written an excellent appreciation of Tyndall as well, which I heartily recommend.
The conference has posted a PDF of Tyndall’s paper—On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction—which Tyndall had presented as the Bakerian Lecture back in February 1861. It’s fascinating to read, because it painstakingly describes how Tyndall conducted his studies with this experimental set-up.
Tyndall noted that the most prominent greenhouse gas in the atmosphere, based on his studies, was water vapor. However, as he recognized, the others could not be ignored. As countless climate scientists have explained to those in denial ever since, carbon dioxide is most influential on changes in climate because water vapor then amplifies its effect.
This diagram summarizes how the greenhouse effect plays into the Earth’s overall energy budget and thereby affects its climate.
Again, once upon a time, little in the above picture was controversial. Scientists would debate precisely what the values of transmitted, reflected and absorbed heat should be (and indeed, they still do), but the general scheme was widely accepted.
Only in recent decades, when so many have been so motivated to wave away concerns about global warming, has anyone tried to dismiss the effects of CO2 on Earth’s climate. They will sometimes try to argue instead that the climate is really determined, directly and overwhelmingly, by the power of the sun.
Many disproofs of that idea have been offered already; let me present just one. And because discussing the Earth’s climate seems to raise so many issues, let’s ignore Earth and look at two other planets.
Mercury orbits closest to the sun, at an average distance of only about 58 million kilometers. It has almost no atmosphere. On the side of the planet away from the sun, since nothing can trap the heat, temperatures can plunge down to only 100 Kelvin, or roughly -280 degrees Fahrenheit. But directly under the sun, when Mercury is at its closest approach, temperatures are estimated to hit about 700 K, or roughly 800 degrees F.
Venus is about twice as far away from the sun as Mercury is: 108 million kilometers. The sunlight it receives is therefore only one quarter as strong. And yet Venus is hotter than Mercury. Because of the thick, CO2-rich clouds that drape Venus, its temperature is about 735 K, or 863 degrees F. Moreover, that is the temperature everywhere on the planet all the time—at the equator, at the poles, during the day, during the night. Venus’s greenhouse atmosphere traps heat so effectively that no area ever cools off relative to the rest.
The sun is powerful, but when it comes to climate, the greenhouse effect is the great equalizer.