Recently someone wrote this to the Cornwall Alliance:

I saw the following comment recently posted online in regard to a climate change column & I’d like to respond to him thoughtfully & intelligently:
 
“CO2 when overproduced acts as a pollutant which our environment can not properly use to make oxygen. It acts as a thermal blanket which raises the temperature steadily. This also harms the oceanic life which plays a key role in converting the CO2.”
 
He mentions 3 ‘facts’ here that I suspect are all suspect, esp. the first one. Can you refer me to any layman-friendly articles that speak to these topics?

How might he respond?

1. The words “when overproduced” essentially assume the conclusion as part of the argument. The relevant question is “What magnitude constitutes overproduction”? And the answer to that varies depending on the circumstance. On Apollo 13, each astronaut was exhaling (as are you and I) about 40,000 parts of CO2 per million parts of the air we expelled from our lungs—but when the spacecraft’s CO2 scrubber failed, that counted as overproduction. When it comes to Earth’s total atmosphere/hydrosphere/lithosphere (air, water, land) system, current atmospheric CO2 concentration is about 412 parts per million, which is less than 1/20^th the concentration at which very minor health problems occur for America’s submariners exposed to it long term; i.e., it’s not a threat to anyone’s health in terms of our respiration. The idea that it’s “overproduced” rests on the theory that its warming effect is large—a theory essentially programmed into the various computer climate models that forecast dangerous warming for the future if atmospheric CO2 concentration continues to rise. But the models’ predictions so far have called for two to three times the observed warming over the relevant period, indicating that they don’t properly depict the relationship between CO2 and global average temperature, but exaggerates it. Hence, the empirical evidence is that CO2’s warming effect is much smaller than the models—and the climate alarmists—assume.
2. Calling CO2 a “pollutant” is highly dubious. CO2 is an odorless, colorless gas non-toxic at more than 20 times the current atmospheric concentration. It is essential to photosynthesis; at about 270 to 280 parts per million, the level for centuries leading up to the Industrial Revolution, plants are essentially starving for it, and under 170 ppm photosynthesis stops and all life on Earth stops. During most of Earth’s history, atmospheric content was around 5,000 to 7,000 ppm, and plants thrived—as did the animals that ate them—and the planet didn’t suffer devastating warmth.
3. Saying that our environment “cannot properly use” CO2 at the present concentration “to make oxygen” is simply false. Plants take in CO2 in photosynthesis and emit oxygen; animals and insects take in oxygen and emit CO2. The increased extent and density of vegetation on the earth over the last 60 years, shown by satellite imagery, have been due in large part to increased atmospheric CO2 concentration—and all that growth of plants has required photosynthesis taking in CO2 and emitting oxygen.
4. CO2 does not act as a thermal blanket that raises temperature steadily. First, it doesn’t act like a blanket. A blanket warms a heat-generating body by preventing convection (the upward movement of warm air). CO2 doesn’t prevent convection. Instead, it absorbs infrared radiation (heat) and re-radiates it spherically; consequently, some infrared bouncing from Earth’s surface back out toward space gets re-radiated back toward the surface, raising near-surface temperature somewhat, while lowering high-altitude temperature somewhat. Second, although the rise in atmospheric CO2 concentration has been exponential and relatively smooth, the measured rise in global average temperature has not been steady. It’s been intermittent, with periodic ups and downs—and since 1999 there’s been essentially no significant upward trend in global average temperature. The non-correlation of CO2 and temperature strongly suggests that CO2 isn’t the control knob for temperature. It contributes, but other factors far outweigh it. Third, the really interesting question is, “How much warmer does a given increase in atmospheric CO2 concentration make the near-surface atmosphere?” The answer to that question appears increasingly clearly to be, “Far less than the computer models have predicted”—probably more on the order of 0.5 to 2 degrees C than the 1.5 to 4.5 claimed by the United Nations Intergovernmental Panel on Climate Change based on the models.
5. The claim that rising atmospheric CO2 content harms ocean life probably refers to the alleged harmful effects of “ocean acidification” (actually a slight decline in the pH of ocean water that still leaves it well on the alkaline side of the pH scale) on coral reefs, but empirical studies indicate that the modeled harm isn’t actually occurring in nature or, when it is, the corals are able to adapt and recover quickly.

To learn more about this and related issues, read Dr. Roy W. Spencer’s books Global Warming Skepticism for Busy People and An Inconvenient Deception: How Al Gore Distorts Climate Science and Energy Policy, both of which are published by the Cornwall Alliance and available through our online store; you can click on the links above to find them.