If you were to take the sum “knowledge” of global warming skeptics and distill it into a short, quasi-readable manifesto, you’d end up with something like Joanne Nova’s “The Skeptics Handbook.”
For someone who claims to have been a “veteran believer in greenhouse gases from 1990 – 2007,” Nova sure has a way of rehashing a lot of the same old tired arguments that climate scientists have been shooting down for years – particularly her central point that there is no evidence to link rising carbon dioxide emissions to higher temperatures (more on that later).
Perhaps the most odious aspect of this handbook is that it seems to be aimed squarely at a younger audience – what with its dumbing down of the science and constant repetition of the same flawed arguments. Having failed to gain ground with the adults, the skeptics are presumably turning to the younger generations now to carry their water.
While I’d encourage anyone who wants a substantive discussion of the science behind climate change to go consult the experts (actual scientists like the Real Climate blogger team, for example) – a revolutionary concept, I know – I’ll do my best to debunk some of Nova’s most egregious arguments over the next few days. I’ll get things started today with her “bottom line”: that adding more CO2 to the atmosphere does not cause global warming.
The easiest way to dismiss this point, as Grist contributor and Texas A&M University Professor Andrew Dessler noted, is to look at Venus’ atmosphere. Though it shares several features in common with our planet – hence its sometimes being called Earth’s “sister planet” – it differs in one crucial aspect: the amount of CO2 in its atmosphere.
In fact, many of its unique characteristics can be attributed to the fact that its atmosphere has such a large mass of CO2 – roughly 97 percent of it. This may help explain why its average surface temperature – around 462°C (or 735°K) – is so high, though there are certainly other factors at play. (The comparison isn’t perfect, of course, since the two planets’ atmospheres differ in other respects, but Venus’ atmosphere does demonstrate that there is a link between higher CO2 levels and higher temperatures.)
If you want a more detailed, science-heavy (and more robust) explanation for why adding more CO2 to the atmosphere will worsen global warming, then you need to understand a little more about how the greenhouse effect actually works. One common refrain from skeptics is that the atmosphere is already saturated with CO2 – in other words, that the greenhouse effect has already reached “its peak performance,” as Nova puts it – so adding more of it, even doubling its atmospheric concentration, shouldn’t make a difference. The problem with this logic is that it ignores the complex, multi-layered structure of the atmosphere by essentially treating it as one unit.
Radiation that leaves and enters the atmosphere must move through several layers. A little of it gets trapped in each one when CO2 or another greenhouse gas absorbs some of its energy; that energy may be radiated back to the ground or, in some cases, used to speed up the surrounding air molecules, causing more collisions and, thus, a slight warming of the layer in which they sit. A fraction of that energy shifts to higher layers and, when they become thin and cold enough, escapes into space.
It stands to reason then that adding more CO2 to the atmosphere should allow the upper layers to absorb more of it. This means that the energy would have to move up higher still in order to escape into space. Because these layers are particularly cold, they don’t radiate heat upwards as effectively and, therefore, a lot of that surplus energy moves back to the surface – resulting in the planet taking in more energy than it emits.
Since the higher layers are the ones that determine whether or not this excess energy leaves the atmosphere (and, thus, how much extra warming occurs), whether or not the surface levels are saturated – and, just to be clear, they’re not – makes little difference.
If that all sounds a bit confusing, and you’re still not clear on the whole saturation argument (or some skeptic has decided to muddle the situation further by bringing up water vapor), just know this:
“(a) You’d still get an increase in greenhouse warming even if the atmosphere were saturated, because it’s the absorption in the thin upper atmosphere (which is unsaturated) that counts (b) It’s not even true that the atmosphere is actually saturated with respect to absorption by CO2, (c) Water vapor doesn’t overwhelm the effects of CO2 because there’s little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and (d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.”
Next time, we’ll bust the skeptics’ claim that the world is no longer warming.