If there’s one thing I hate more than anything, it’s pointless rhetoric. Physics has made me this way since physics trains you to wade through the BS. And with most issues, there’s BS on both sides. So, if you’ve been paying attention to such things, perhaps you were aware of this. Specifically, an error in US climate data has recently been discovered by climate scientists that has slightly rearranged the list of “hottest years on record.” Now, here’s where the rhetoric comes into play:
Anti (or anthropogenic?) global warming (AGW) side:
Update: Thanks to wolfgang for bringing this potential confusion to my attention. I know I should be good about getting this (what AGW stands for) right, but, regardless, on the site I link to above and below, the AGW didn’t support the notion that humans are having an affect on global warming. So regardless of what AGW stands for as an acronym, they don’t believe in the whole “carbon contributes to global warming” think. So, anyway, they (the AGW community) have been all over this as definitive proof that global warming isn’t happening or that we’re simply in a natural warming trend (i.e. humans aren’t causing it) despite the fact the (if you check out the link again) rearrangement wasn’t terribly drastic. No single year moved more than a place or two on the list. Nonetheless, the AGWs act as if suddenly the 1990s turned out to be a mini-ice age.
The effect of the change mentioned above, in addition to a minor rearrangement of the hottest years on record, was also to change the estimate for the average global temperatures for certain periods. Specifically, the climate scientist I mentioned before says that the “net effect of the change was to reduce mean US anomalies by about 0.15 ºC for the years 2000-2006.” An anamoly is how far a given year was from the average. So, further down he reports that the US average temperature for 2002-2006 was 0.66 ºC and for 1998-2006 was 0.79 ºC. He then (actually in various places) dismisses this change in the mean anamoly as insignificant since it is only a fraction of a degree Celsius. But note that the mean temperature for the period of 1930-1934 was 0.63 ºC which means, the four-year cycle ’02-’06 was an increase in 0.03 ºC over ’30-’34, far smaller than the amount by which the mean US anamolies were decreased! Um, huh? If you’re going to tout that 0.15 ºC is not a significant change, then you need to remember what you’re comparing it to (or what your readers think you’re comparing it to.
With that said, astronomers have long known about the “greenhouse effect” since that’s what has happened on Venus (though for obviously different reasons) sometime in the last couple million years or something (and, yes, Mars has a load of CO2 but the reason it can’t be compared to what’s happening on earth is because it has a considerably smaller mass which affects the make-up of the atmosphere, etc., etc.). Anyway, here on earth, the evidence from other sources seems pretty clear that, while we are definitely in a natural warming cycle, the rate of warming appears to be increasing, so it’s getting hotter faster than it should.
So, as a physicist, I’ve been attempting to weed through the rhetoric on both sides. Data analysis is nice and it can tell you a lot, but one thing it doesn’t tell you is what is really going on. So, I’ve decided to tackle the global warming issue from a quantum/statistical mechanical point-of-view, looking at just what energies are absorbed and reemitted by normal air (N2 and O2) and by CO2, as well as looking at the effect of added CO2 on the heat capacity of the mixture.
Quantum mechanically, the way global warming has been explained to me is that the CO2 absorbs photons reflected by earth’s surface that normally pass right on through on their way back out. The absorption briefly bumps up the energy level of the CO2 (likely electronically in visible wavelengths and rotationally and vibrationally for IR and microwave), and then the CO2 settles back down reemitting these photons. However, any time you have a large, random ensemble of atoms or molecules that emit energy, the energy is emitted in all directions. So, of these photons that normally pass right on through on their way out of the atmosphere, about half (think hemispherically) get sent back down to the surface (actually a bit less since some is reabsorbed by neighboring molecules).
First of all, this explanation demonstrates that the term “greenhouse effect” is inaccurate. In a greenhouse, the ultra-violet radiation gets permanently stuck inside “the greenhouse” (or your car, for example). In the global warming case, the photons make it out eventually, but it takes longer to get rid of them since some get sent back down before they can go out again (some, obviously, get sent down several times – I should mention it’s not necessarily the same photons, rather it’s a percentage of the aggregate). No big deal, right? Well, if we could make the night longer or winter longer, we’d be good to go, meaning that the effect of the “greenhouse” gases on the atmosphere is to slow down the daily and yearly heating and cooling rates such that excess heat builds up in the atmosphere.
Now, what I want to find out is, is this the definitive explanation? It is at the very least self-consistent, but whether it truly explains global warming will depend on just what wavelengths (energies) the CO2 absorbs that the O2 and N2 do not (or if this statement is true).
In any case, the short summary is to say that I’m interested in what’s really going on sans the hype from both sides of the aisle.
However, I will point out one little curious note that is often overlooked. While everyone is debating the effect of carbon in the atmosphere on global warming, no one is talking about an expense that must be paid for the burning of hydrocarbons: oxygen. While it is not presently a major concern, note that CO2 gets its O2 from the air. So for every carbon atom we send into the atmosphere via the burning of hydrocarbons, we take out an O2 molecule. No big deal, right? Lots of air to go around? Well, consider this. CO2 is measured currently at about 385 parts per million in the atmosphere. If we doubled the amount of straight “carbon” we’re putting into the atmosphere, we’re simultaneously taking that much O2 out. The Navy (among others) can tell you that once CO2 constitutes about 1% of the air a person breathes, it can begin to cause headaches and other mildly troubling health symptoms. Above 1%, of course, it only gets worse. How does the Navy know this? Subs. A colleague of mine was a submariner in the Navy and had one commanding officer who liked to stay down for awhile (this was in the 1970s – technology may have improved) and this inevitably led to many of the crew getting CO2 headaches. So, if you’re not careful, you can reach that 1% concentration faster than you think because for every CO2 molecule you introduce, you also eliminate an O2 molecule (which is what keeps you alive). Just some food for thought…