My father (who is apparently a member of a newly discovered North American club) is a Global Warming skeptic. I think I’ve convinced him recently, however, that CO2 is indeed increasing in the atmosphere at a dramatic rate and that increase is of man-made origin. Being an appropriate skeptic, he correctly asks, “CO2 is increasing … So What!?”

Here’s why CO2 build-up in the atmosphere is meaningful:

Our atmosphere is relatively transparent to visible light. Therefore much of the energy from the sun passes through our atmosphere and is “absorbed” by the surface (which is relatively opaque to visible light). The surface then begins to warm and as a result re-radiates the energy. This re-radiation occurs at a different wavelength then the incident energy and is generally shifted toward the near infrared (commonly referred to as “heat waves”). Our atmosphere however, is not as transparent to the near infrared or “long wavelength” end of the visible spectrum and so this energy is “captured” by the “greenhouse gases” in our atmosphere and the resulting is a warming of the atmosphere. You know that the atmosphere is not as transparent to the long wavelength, red end of the spectrum because “the sky is blue”. If the atmosphere was equally transparent to all visible light then, even during the day, the sky would be pure black (like pictures from the Moon). You also know that we’re warmer with an atmosphere than we would be without it because you know what happens when you cover your own body with a blanket.

Everything above is without debate. Now, however, it’s important to attempt to model this precisely and that is difficult. If the earth were a pure “blackbody” then it would be relatively easy. For example, we could assume that all light energy from the sun that hit a “disk in space” of diameter equal to the earth’s diameter was absorbed completely and thermal equilibrium were achieved. Using the Boltzmann’s Law we could then determine the temperature a blackbody globe would be to emit this much energy (thermal equilibrium). This predicts a temperature of about 42 Fahrenheit. This immediately complicates however because the earth doesn’t absorb completely and some of the energy is reflected. This is known as the earth’s albedo and is roughly estimated to be about 68% absorption efficiency. In addition, we have to estimate how effective the atmosphere is in capturing the energy re-emitted by the earth. This is known as emissivity, i.e. what percent of the energy radiated by the earth is emitted out from the atmosphere. This is roughly estimated to be 61%. Using these two parameters for earth’s light absorption and atmospheric emission we then predict a temperature of 56 Fahrenheit. This is a fairly simple model but it gets pretty close to the actual average earth’s temperature which is about 55 to 56 Fahrenheit. (This model is further explained here and here’s a simple excel spreadsheet that implements these calculations).

OK, now we’ve got a pretty good handle on what affects the temperature of our climate: the incident energy from the sun, the reflectivity or albedo of the earth’s surface and the energy absorption or emissivity of our atmosphere. If any of these parameters change, then the temperature we experience is going to change. So the simple answer to “Why is CO2 build-up meaningful?” is that the amount of CO2 in the atmosphere can change the emissivity of the earth’s atmosphere. According to our model, a one percent change in emissivity will result in a 2 degree Fahrenheit rise in temperature. Note also that in the model a one percent change in albedo also results in a 2 degree change in temperature. This is why the polar ice caps are considered of such importance, the size of the “white” polar ice caps (areas of high reflection) is a large determinant of the earth’s albedo.

Again, at a high level, there no debate in any of these points. The earth is a physical object that obeys the laws of thermodynamics and it’s made of materials that have physical characteristics. If these physical characteristics change (e.g. albedo, emissivity), the the point of thermal equilibrium will change according to the laws of thermodynamics. What’s also true, however, is that precisely measuring and predicting these effects on a global scale is extremely difficult and highly debatable. The measurement of average surface temperature of the earth is extraordinarily hard, especially when trying to reproduce a backward history of these measurements. Predicting and measuring the average emissivity of the atmosphere, especially as a function of the atmospheric make-up is again, an extraordinarily difficult problem to make complete and precise. To further complicate the model, the two parameters emissivity and albedo interact. A lot of work in this area is subject to debate and, unfortunately, when driven by a political agenda often complete crap. A relatively objective look at the complexity involved indicates why so much is available for debate. It doesn’t change the reality that if we put enough CO2 into the atmosphere, we’re going to change the temperature of the climate, that’s just physics. (Note: CO2 is only one of the “greenhouse gases” a relatively poor name for gases that absorb energy in the infrared spectrum such as water vaper, ozone, CO2, nitrous oxide and methane)

So let’s stay with “An Un-confused Truth”, (whether or not convenient): The earth is a natural system that is currently in a state that supports complex life and is especially conducive to the dominance of man. This particular state of the earth, however, is not it’s only possible state and, in fact, not the state that it’s been in for long. The earth has existed as a solid sphere for about 4.5 Billion years. A unique characteristics of the earth right from the start was that its distance from the sun allowed for water (note our simple model predicts a temperature of 42 Fahrenheit, right where H20 is a liquid). It turns out that water and a bit of methane gas is a great cocktail to allow complex carbon molecules to occur and bacteria (or prokaryotes) seem to have existed on the earth for nearly 4 of its 4.5 Billion years. The creation and proliferation of bacteria is what created the atmosphere and the atmosphere warmed the earth to above 50 Fahrenheit creating a globe whose surface is covered mostly by oceans. The nursery of the oceans and about three to three and half billion years of incubation allowed complex animal life forms to emerge. The exact conditions that have allowed man to be the dominate complex life form have existed for about 200,000 years. Those conditions include a mild and consistent climate that let’s man’s intelligence and memory find food year round. And a long term stability that has allowed our species to develop a continuous memory of nearly 10,000 years to form what we loosely call “knowledge”. But please note the time scale: if the 4.5 Billion years of earth’s existence were a timeline that spanned from the tip of your right hand across your shoulders to the tip of your left hand, then you could wipe out the time of man by swiping a nail file across the tip of your left middle finger(*).

The belief that this world is in a stable, self-correcting state that has existed and will exist forever is naïve. The reality is that we exist in a highly unusual place: a relatively small and solid planet, just the right distance from a relatively small and stable star that allows water to exist as a natural form; and that condition has been highly stable for approaching 5 Billion years. Given time, it will change. The responsible behavior for us, given our knowledge is to try to preserve the gift of our environment as best we can. Our lives depend on it.

(*) – The analogy of the ‘a nail file wiping out the time of man’ is one of my most remembered passages from Bill Bryson’s excellent book A Short History of Nearly Everything. You should read it.

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