Friday, April 23, 2004

I wrote this as a letter to the editor back in 2001, but not much has changed in the basic facts. Unfortunately, there is generally not much discussion of the most basic facts, which led to the writing of this letter.

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Climate Change 101: What the Cynics Don't Say

In light of all of the hot air swirling around the topic of climate change, some basic facts about CO2 must be remembered.

First, the greenhouse effect has been on earth since it's creation, and is responsible for keeping the earth about 59F warmer than otherwise. Second, CO2 only contributes about 5% of the 59F of warming (i.e., about 3F). About 90% comes from water vapor, and 5% or so comes from other gases.

While natural sources generate 700 billion tons of CO2 yearly, all of that is reabsorbed by plants (and some by geochemical processes) to create new vegetation, much of which fed animals who then released it once again as CO2. Of the extra 24 billion tons emitted by humans (mostly generated by fossil fuels formerly locked away deep underground), only about half gets soaked up by the biosphere. The rest has been steadily accumulating in the atmosphere, raising concentrations from 0.0275% 275ppm (pre-industrial) to 0.0375% (currently), and likely well beyond 0.055%.

Climate cynics argue that this annual increase in CO2 levels is harmless on the grounds that 1.7% is a small number. Of course, I would not be harmed by a 1.7% increase in body weight, but to gain that much every year for 40 years could cause severe health effects. Likewise with CO2.

A doubling in CO2 concentrations can be expected to lead to a doubling of the greenhouse warming from CO2, i.e., about a 3F increase in global mean temperature. Furthermore, human activities are also increasing other more potent greenhouse gases such as nitrous oxides, methane, CFC, etc., implying an even larger temperature increase. While there are many natural processes that can dampen these temperature increases (such as fluffy low altitude clouds), there are others that can exaggerate them (such as wispy high altitude clouds). The best guess currently, after accounting for known factors is that we can expect a 2.7F to 7.2F [Science News, Mar 10, 2001] increase in temperature.

Climate cynics also like to point out 1000's of experiments showing that higher CO2 levels stimulate plant growth. While it's nice to know that, say, ryegrass and petunias bulk up with more CO2 (that's 2 experiments), they neglect the key experiments which better show the impact on human life and economy.

First, growth rate are not sustained, e.g., long term experiments with pine trees show that the fertilization effects stops after 3 years.

Second, plants produce other things than bulk mass when growing, for instance, pollen. Rag weed produces half the pollen at past levels of CO2 and twice the pollen at future levels of CO2. So, if it seems like your allergies have been getting worse, well, get used to it. It's going to get worse. This also implies that much of the recent increase in asthma can be attributed to the matching rise in CO2, as rag weed can trigger asthma.

Third, the extra bulk of CO2 fertilized plants is less nutrituous (being nitrogen poor, and hence, protein poor). In experiment, Sheep longer to digest it, and take longer to mature when fed CO2 fertilized fodder. Some insect species suffer; other's, like aphids, thrive.

Climate cynics also claim that the recent rise in average global temperature and the rise in CO2 levels are completely coincidental--that while we have been dumping huge amounts of proven greenhouse gases into the atmosphere, (1) their known heat trapping properties are counterbalanced by unknown mechanisms, and (2) natural cycles are causing the Earth to warm in proportion to the amount of increased CO2 (plus other man made greenhouse gases).

After many years of study, alternative warming mechanisms are still highly speculative. While changes in radiation from the sun are a leading contender, incorporating known fluctuations in solar radiation into climate models only strengthens the case for man made climate change. While climate over the past millenia can mostly be explained by variation in solar radiation & volcanic emissions (which leave traces in the geologic record), no solar & volcanic variations have been observed in the last century that can explain the sudden rise in average global temperature which so closely matches the rising CO2 levels. These factors do neatly explain most of the climate fluctuations that do not match the increase in CO2 levels (such as the warming in the 1940's), but only about 1/3 of the current warming trend can be attributed to increased solar input (based on observed data).



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