In previous posts (here and here) I showed that Senator Orrin Hatch (R-UT) was playing it a little fast and loose in his Climate Change 101 web page. That is, he says he wants climatologists to be more open-minded toward criticisms about the mainstream view of climate change (a worthy goal,) but then when he starts listing criticisms, he does things like 1) reproducing fabricated data he got from a non-scientist, and 2) citing a single paper that has since been shown to be severely flawed as the absolute last word that “disproves” the idea that humans cause significant global warming by pumping massive amounts of greenhouse gases (especially CO2) into the atmosphere. In other words, it sure seems like Senator Hatch is simply parroting whatever arguments he WANTS to believe, rather than going to all the work of carefully examining the evidence.
I realize that this is a serious charge (at least if you value intellectual honesty.) Is Senator Hatch really just parroting arguments that he doesn’t fully understand? In this post I’m going to take apart the Senator’s statements about CO2, which is thought to be the major culprit in human-caused global warming, to show that he really hasn’t done his homework. In fact, many of his statements are simply red herrings–decoys that initially sound like plausible arguments, but turn out to be more distracting than informative.
1. Senator Hatch tries to convince his readers that adding CO2 to the atmosphere might actually be a good idea! The implication is that mainstream climate scientists haven’t taken positive effects into account before pushing the idea that we should cut our emissions.
Climate contrarians often begin by trying to give CO2 a public relations boost, and politicians, especially, like to call it “The Gas of Life.” Consider how Senator Hatch riffs on this common theme.
Several scientific studies conclude that with higher CO2 levels in the air, plants become more hardy and thrive better even with significantly less water. For this reason, it is a common practice for commercial greenhouses to pump in CO2 to boost plant growth. CO2 is the ultimate plant food.
It’s quite true that elevated levels of CO2 do boost the growth of SOME kinds of plants. Everyone who studies plants knows this, including (Senator Hatch might be surprised to find out) the botanists and ecologists who study the effects of global warming on plant life. So the question isn’t whether there are any positive effects of increasing atmospheric CO2. Rather, the question is, “AT WHAT POINT the negative effects of global warming (like increased incidence of drought) start to OUTWEIGH the positive effects?”
Has the IPCC ignored the evidence for positive effects, as Senator Hatch apparently wants his readers to believe? That’s actually pretty easy to check out. I went to the IPCC website and opened up the 2007 Working Group 2 Report, which is about “Impacts, Adaptation, and Vulnerability.” I scanned through the table of contents and found that Ch. 5 is about “Food, Fibre, and Forest Products”–i.e., plant stuff–and then to Section 5.8.1, which has the “key findings and conclusions” for the chapter. Senator Hatch should read it, because it has all kinds of statements like the following.
While moderate warming benefits crop and pasture yields in mid- to high-latitude regions, even slight warming decreases yields in seasonally dry and low-latitude regions (medium confidence).
The preponderance of evidence from models suggests that moderate local increases in temperature (to 3ºC) can have small beneficial impacts on major rain-fed crops (maize, wheat, rice) and pastures in mid- to high-latitude regions, but even slight warming in seasonally dry and tropical regions reduces yield. Further warming has increasingly negative impacts in all regions [5.4.2 and see Figure 5.2]. These results, on the whole, project the potential for global food production to increase with increases in local average temperature over a range of 1 to 3ºC, but above this range to decrease [5.4, 5.6]. Furthermore, modelling studies that include extremes in addition to changes in mean climate show lower crop yields than for changes in means alone, strengthening similar TAR conclusions [5.4.1]. A change in frequency of extreme events is likely to disproportionately impact small-holder farmers and artisan fishers [5.4.7].
Experimental research on crop response to elevated CO2 confirms Third Assessment Report (TAR) findings (medium to high confidence). New Free-Air Carbon Dioxide Enrichment (FACE) results suggest lower responses for forests (medium confidence). Crop models include CO2 estimates close to the upper range of new research (high confidence), while forest models may overestimate CO2 effects (medium confidence).
Recent results from meta-analyses of FACE studies of CO2 fertilisation confirm conclusions from the TAR that crop yields at CO2levels of 550 ppm increase by an average of 15%. Crop model estimates of CO2 fertilisation are in the range of FACE results [22.214.171.124]. For forests, FACE experiments suggest an average growth increase of 23% for younger tree stands, but little stem-growth enhancement for mature trees. The models often assume higher growth stimulation than FACE, up to 35% [126.96.36.199, 5.4.5].
So the fact is that the IPCC has tried to take positive effects like increased plant yields into account. THEY are the ones who have tried to see how all of it balances out, while people like Senator Hatch are the ones trying to ignore negative effects. Pot, meet kettle.
The Senator does seem to understand the concept of net results, though.
There is also some disagreement among scientists as to whether global warming – regardless of its cause – would result in a net benefit or detriment to life on earth. Scientific studies demonstrate overwhelmingly that humans tend to fare better during warming spells than periods of cooling.
The problem with this is that the scientific debate is not about whether warming is “good” or “bad”. Change happens, but when important changes are both sustained and rapid, the rest of nature has a hard time keeping up. Personally, I have never noted any scientists arguing that global warming will be good for the world, who don’t also believe that the IPCC has overestimated the likely amount of warming over the next century. As I showed in my previous posts, these scientists are few and far between.
2. Senator Hatch implies that adding CO2 to the atmosphere can’t possibly cause much warming, because it isn’t even the most abundant greenhouse gas, and most of the CO2 in the atmosphere is natural, anyway.
Here’s how he puts it:
The main GHGs are water vapor, CO2, and methane. However, water vapor is, by far, the dominant GHG. In equal volumes, water vapor has a significantly higher warming factor than CO2. Besides its higher warming factor, water vapor is also much more prevalent as a GHG than CO2. The volume of water vapor in the atmosphere is not constant, but the U.S. Energy Information Agency estimates that water vapor makes up 95 percent of all greenhouse gases, naturally emitted CO2 makes up only 4.7 percent of GHGs, and human-emitted CO2 makes up only 0.3 percent of all GHGs.4 To reemphasize this fact – because it is so often under emphasized by the popular media and the UN – CO2 has significantly less power to warm per volume than water vapor, AND it makes up a much smaller volume of GHGs compared to water vapor.
Methane is a powerful but very minor greenhouse gas in terms of volume and is, therefore, not calculated in the graph below.
All these facts seem to be correct, but some of them are tailored to be misleading–i.e., important background is left out. For instance, while it’s true that about 94% of atmospheric CO2 is from natural sources, it’s also true that the total atmospheric carbon dioxide has increased about 40% since pre-industrial times, when it was fairly stable for thousands of years. So where did all that manmade CO2 go? The answer is that the CO2 in the atmosphere is in short-term equilibrium with CO2 dissolved in shallow ocean water. Even some people who have taken a few chemistry courses don’t realize that in an equilibrium system, the forward and reverse reactions are still going. We pump extra CO2 into the atmosphere, and some of it gets dissolved in shallow ocean water until a new equilibrium is reached. However, even at equilibrium, the atmospheric and dissolved CO2 are constantly exchanging. Since there is so much more CO2 dissolved in the ocean, the manmade CO2 molecules in the atmosphere gradually get diluted by the natural ones, but this does not change the new equilibrium concentration in the atmosphere. Bottom line: Even though only 6% of the CO2 molecules in the atmosphere are manmade, almost a third of the CO2 concentration in the atmosphere is there due to human activities.
[UPDATE: My friends tell me that the last paragraph is hard to understand, so here are some explanatory notes. 1) We pump extra CO2 into the atmosphere, which has raised the concentration by 40%, so far. 2) The CO2 in the atmosphere exchanges with that dissolved in the shallow ocean, making the proportion of man-made CO2 molecules in the atmosphere go down, while the proportion of man-made CO2 in the ocean goes up. Meanwhile, the total CO2 concentration in the atmosphere doesn't go down as much as the man-made CO2 concentration. 3) We can tell how much of the CO2 is from burning fossil fuel by looking at the ratio of C-13 and C-12 isotopes. This explanation is a little oversimplified, but there is a voluminous literature on how difficult it is to teach chemical equilibrium correctly, so I'm not going to accomplish it in a couple paragraphs. Anyway, you don't need a better explanation (Jedi mind trick).]
Another example is how Hatch implies that adding CO2 can’t possibly have much of an effect, because water vapor is by far the dominant greenhouse gas. Again, it’s true that water vapor is the big dog on the block, but he’s missing some vital information. We are talking about CHANGES in the temperature due to CHANGES in greenhouse gas concentrations. The problem with water vapor is that there is a limit to how much the atmosphere can hold at a given temperature. If the humidity gets too high, the water vapor condenses and falls out of the atmosphere as precipitation (e.g., rain). Much of the atmosphere fluctuates around this limit, so that if we decided to build machines to pump extra water vapor into the atmosphere, it wouldn’t have much of a long-term temperature effect because the extra gas would quickly condense and precipitate out. If we keep pumping CO2 into the atmosphere, however, it will keep building up, and so CHANGES in CO2 concentration can be a cause of long-term global temperature CHANGE.
Even though water vapor can’t drive long-term temperature CHANGES by itself, it can enhance changes caused by other drivers. If the temperature starts going up because of increased solar radiation or increased CO2, for example, the atmosphere can hold more water vapor. (If you don’t believe me, read the Wikipedia page on relative humidity.) Since it’s a greenhouse gas, the temperature will go up even more. This isn’t speculation–it’s basic physics. But for Sen. Hatch, this is just an “assumption”.
The small role CO2 plays as a greenhouse gas explains why the IPCC climate models do not attribute warming directly to human-emitted CO2. Rather, the models incorporate an assumption that the very small amount of warming from human CO2 creates an increase in water vapor and a decrease in clouds, and this new water vapor – which has a greater warming factor than CO2 – combined with fewer clouds actually creates the additional warming that has been the cause for alarm. This indirect warming effect is referred to as positive feedback.
Although I grant that the cloud feedback is somewhat controversial, recent work shows that it is probably fairly small, and probably positive. The idea that water vapor feedback is positive is totally non-controversial. (For background on the water vapor feedback, see this lecture by Prof. David Archer of the U. of Chicago.) Even scientists like Dick Lindzen, whom Sen. Hatch cites, don’t argue that the water vapor feedback is negative, but rather that other feedbacks (like the cloud feedback) are more strongly negative than commonly believed.
In summary, Senator Hatch throws out a number of facts about CO2 that are interesting, but insufficient to show how this gas affects global temperature, or its net effect on plant life. I don’t believe he is intentionally throwing out red herrings, but the fact is that if he had spent the time to become truly informed before lecturing the scientific community about how they have it all wrong, these kinds of arguments wouldn’t have impressed him.