Warming Water

So Lola and I build a fire last evening and turn off the furnace. This morning the house is a chilly 57 degrees in the kitchen. I take a shower to get some water vapor in the air and the house warms up. I don’t think this is cause and effect but any completely accurate description of the total energy within my house needs to account for the water.

The Climatic Effects of Water Vapor: (pdf) There are a number of popular misconceptions about the greenhouse effect, notably that it is a bad thing. On the contrary, the greenhouse effect is a significant factor in making the Earth habitable. Without it the average temperature on Earth would be lowered by about 30 K, which would make most of the planet’s surface decidedly chilly. Furthermore, it is the water vapour in the lower 10 km or so of the atmosphere, rather than man-made carbon-dioxide emissions, that contributes most to this warming effect.

The mainstream media simply publish anything they are given and they are exceptionally unqualified to critically analyze science writing. The biggest error of omission in almost every piece broadcast or written about climate science is the role of the primary greenhouse gas. Have you ever heard this explanation on CNN or read it in the NY Times?

Air is largely composed of the diatomic molecules nitrogen and oxygen. So why is the transport of light through our atmosphere dominated by trace amounts of triatomic molecules such as water, carbon dioxide and ozone? After all, these molecules are only present above our heads at a level of about one part in 100 000. The answer lies in the physics of the individual molecules involved. Molecules absorb radiation at characteristic wavelengths that excite one or more of their rotational, vibrational or electronic degrees of freedom.

But what is so special about water that makes its absorptions extend all the way from the far infrared to the near ultraviolet? The simplest answer to this is that water, unlike the other triatomic species, contains two atoms of hydrogen. The presence of hydrogen atoms has two important effects. When a water molecule rotates about its centre-of-mass – which is near the oxygen atom – it does so with small moments of inertia. This leads to a very wide-ranging rotational structure that causes absorption bands for all types of transitions to extend over large regions of the spectrum.

The spectroscopic data that are required to model longwave atmospheric absorptions are generally well characterized. When these data are put into atmospheric models, water turns out to be responsible for about 60% of the greenhouse effect, while the much reviled carbon-dioxide molecule accounts for just 26%. Ozone accounts for 8%, and methane and nitrous oxide – the atmospheric concentrations of which have been increased by human activity – contribute a further 8% to the greenhouse effect.

Molecules consisting of three atoms are the ones absorbing most of the energy because their electrical charge is not evenly distributed. In simple terms, the charge polarity of three atom combinations allow energy to be absorbed in multiple ways with multiple effects on the activity of the molecule. And no, reversing the polarity will not send you into hyperspace or disengage a tractor beam. Of the triatomic molecules, water is by far the most important factor in moderating radiant energy effects.

The behavior of the planet arises from the physics of the atoms and no computer model can accurately recreate real observational data and, therefore, can not accurately predict the future. It is wise to be skeptical about any global warming article that does not discuss the dominant role of water in the way the atmosphere handles energy input from the sun, and subsequent heat loss from the surface of the planet.