One thousand ppm might be better

The Australian government is bent on enacting a carbon-emissions tax that has no responsible justification other than recently re-hashed advice designed to justify an emissions tax. Little wonder, then, that polling shows voters are strongly opposed to the tax, despite widespread their apparent conviction that the climate is warming and their acceptance that warming is at least partly caused by human action .

The “Newspoll” does not ask the most important question: is climate warming an imminent threat that calls for government action. The government itself has not produced a convincing answer to that question. The most diligent of its advisors, Ross Garnaut, has failed to support the hypothesis of dangerous man-made warming except by a leap of faith: a “balance of probabilities” that rests, ultimately, on appeal to an authority (the IPCC) whose credibility is in shreds.

No sound argument relies on an appeal to authority, but a deep understanding of a complex problem sometimes produces insights that can be communicated with surprising simplicity. One recent example is this article on the contribution of greenhouse gasses to climate change by Princeton University professor of Physics, William Happer from the journal First Things.

Happer makes several familiar criticisms of the “moral epidemic” of climate-dread that has infatuated public science and political institutions in the United States, Europe and Australia. But he also calls attention to some simple questions that are not being asked. For example: what is the desirable and tolerable level of atmospheric CO2, given its essential role in photosynthesis.

The minimum acceptable value for plants is not that much below the 270 ppm preindustrial value. It is possible that this is not enough, that we are better off with our current level, and would be better off with more still. There is evidence that California orange groves are about 30 percent more productive today than they were 150 years ago because of the increase of atmospheric CO2.

Although human beings and many other animals would do well with no CO2 at all in the air… the Navy recommends an upper limit of about 8000 ppm for cruises of ninety days, and nasa recommends an upper limit of 5000 ppm for missions of one thousand days, both assuming a total pressure of one atmosphere. Higher levels are acceptable for missions of only a few days.

We conclude that atmospheric CO2 levels should be above 150 ppm to avoid harming green plants and below about 5000 ppm to avoid harming people. That is a very wide range, and our atmosphere is much closer to the lower end than to the upper end [PWG: about 390ppm]. The current rate of burning fossil fuels adds about 2 ppm per year to the atmosphere, so that getting from the current level to 1000 ppm would take about 300 years—and 1000 ppm is still less than what most plants would prefer, and much less than either the nasa or the Navy limit for human beings.

Happer’s full paper is well worth reading for the perspective of a physicist whose independence of climate-science funding means that he joined with about 200 other members of the American Physical Society in their successful 2009 petition against the extraordinary (possibly, self-interested) obeisance of the Society’s Council to the “incontrovertible” conclusion that man is responsible for recent warming.

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