A reader has posted a claim about climate change that I have responded to in the past, but would like to respond to again.
It is a type of argument that, I hold, no rational person truly concerned with reaching a reasonable conclusion about climate change would offer.
The irrationality of the argument takes a little bit of demonstration, but the demonstration is solid.
The position under discussion is:
There is scientific models that show 2 ppm of CO2 is increasing in the environment each year. Are you aware that only 3% of this 2 ppm can be attributed to man?
I need to correct this a bit. It is actually 3.5 ppmv (parts per million by volume) per year. But this will not affect the logic of the objection.
Imagine that you own a tank partially filled with water. Each year, 210 gallons of water flow into the tank, and 210 gallons of water flow out of the tank. For 10,000 years, the level of water in the tank has stayed quite close to 270 gallons.
Note: For 10,000 years, atmospheric CO2 concentration has been hovering around 270 ppmv. Deviations from this have been small.
Now, somebody opens up a faucet that starts adding 7 gallons to the tub every year. After he turns on the faucet, you notice that the volume of water in the tub increases by 3.5 gallons per year.
Note: This corresponds to the 7 ppmv that humans are adding to the atmosphere each year, and the measured increase in atmospheric concentrations of 3.5 ppmv per year.
This happened quite a few years ago, and the volume of water in the tank is now 380 gallons rather than the traditional 270 gallons.
Corresponding to the current 380 ppmv concentration of CO2 in the atmosphere.
In this case, the 7 gallons of water entering the tub from the faucet represents only 3.3% of the total volume of water entering the tub.
Yet, given the following facts: (1) That the volume of water in the tub has been in equilibrium for 10000 years, (2) none of the other sources of water have changed their flow (the only source of increased volume of water entering the tub is what is coming out of the faucet), and (3) the increase in the volume of water (3.5 gallons per year) is half the volume that is coming out of the faucet (7 gallons per year) . . .
The only reasonable conclusion to draw is, of the 7 gallons going into the tub, half of it is flowing out again, and half of it is remining in the tub causing the volume of water in the tub to increase by 3.5 gallons per year.
Now, this is intuitive. In normal circumstances, people wouldn't even think twice about this. They open the faucet. They see a water volume that had been previously unchanged start to increase. They say that opening the faucet is causing the water volume to increase. It's a simple inference that nobody would find tricky.
However, when it serves a political or ideological purpose, we see that it is easy for a person to blind themselves (or intentionally attempt to blind others) to what would be a simple causal inference by making the totally irrelevant claim, "It is 3% of the volume of water flowing into the tub." It doesn't matter. The volume of water in the tub wasn't changing until the faucet was turned on and, if you turn off the faucet, the volume would return to normal. The faucet is 100% responsible for the change in volume in the tub.