They’re at it again. Al Gore Tweets “Continued carbon pollution threatens humanity’s future”. Leave aside the technical quibble that he seems not to know the difference between carbon and carbon dioxide. The huge error in his Tweet is, of course, that CO2 is not a pollutant at all.
Let’s stand back and think about it. CO2 is a trace gas in the atmosphere, currently at a level of 400 parts per million. That’s tiny. It’s 0.04% of the atmosphere. CO2 is a natural, harmless, invisible, odourless, non-toxic gas. It is not only harmless — it’s essential to life on the planet. Imagine a world without any CO2 at all. All plants would die, and consequently all animals would die too.
Of course CO2 is also a “greenhouse gas”. Indeed in our hypothetical CO2-free world, we would be so cold that we should have glaciation over the whole planet, even at the equator – the “Snowball Earth” scenario. But the warming effect of CO2 is not linear (forgive me, I used to study mathematics). That is, the increase in the warming effect of additional CO2 depends on how much you have already. The more you have, the less effect any given addition will make. If we were at 20 ppm, a doubling to 40 ppm would have a significant effect (approximately +1oC). But when we’re at 400 ppm, an extra 20 ppm makes very little difference. In fact the warming effect is governed by a negative logarithmic equation. A doubling of CO2 will always have the same effect. To get the same 1oC warming now you’d need not an extra 20ppm, but an extra 400 ppm — a doubling from today’s level.
You can readily see that this gives a curve that flattens as the CO2 rises – a law of diminishing returns. And we’re already so far up the curve that further increases will be very small.
I should qualify my 1oC per doubling figure. The IPCC uses a figure of around 3oC, which better fits their alarmist theory. They recognise the basic 1oC figure, but argue that there are positive feedbacks (primarily water vapour) which increase the effect.. But they are unable to demonstrate those positive feedbacks. Meantime other scientists point to negative feedbacks (for example, cloud cover and albedo), and some believe that the negatives may outweigh the positives, leaving the sensitivity of climate to CO2 even less than 1oC per doubling.
Al Gore in his infamous film “An Inconvenient Truth” demonstrated a close correlation between atmospheric CO2 levels and temperatures. Such a correlation is strong evidence for causation. But it does not of itself tell you which of two phenomena is causing the other. It doesn’t tell you the direction of causation.
Al Gore simply assumes that CO2 causes temperature rises, and proposes a plausible mechanism for such causation – the greenhouse effect. But what if it were vice versa – the temperature causing the elevated CO2 levels? Here again we have a plausible mechanism. There is around fifty times as much CO2 dissolved in the oceans as exists in the atmosphere. Cool water retains dissolved gases better than warm water. Warming can cause dissolved gases to leave the ocean for the atmosphere.
So which causes which? It is a fundamental principle of science that effects cannot precede causes. So which comes first, the chicken or the egg? If we examine the data on which Al Gore relies for his correlation, we find that the peaks of temperature precede the peaks of CO2 levels by around 800 to a thousand years. Therefore temperature causes elevated CO2, not vice versa. And the temperature changes are driven primarily by solar and other astronomical factors. Warmists blame the steadily increasing level of atmospheric CO2 in recent decades on human activity. But it could just as well be caused by the natural cyclical warming of the planet as we leave behind the Little Ice Age and move into a new 21st Century Optimum.
While the correlation is fairly close over the last 600,000 years, it does not stand the test of deep time. Go back many millions of years in Earth history, and it breaks down completely. There have been times when atmospheric CO2 levels have been as much as ten or even fifteen times higher than today, and those periods were not associated with elevated temperatures, still less “runaway global warming” or “tipping points”. The very long-term trend in CO2 is down, and biologists tell us that if we got down to around 200 ppm – only half of today’s level – we could see a dangerous drop in plant growth.
I was astonished to learn a few years back that horticulturalists who raise tomatoes in greenhouses routinely bring in tanks of compressed CO2 and release it in the greenhouse to raise CO2 levels from an ambient 400 ppm to three times that level – 1200 ppm. Why? Because their tomatoes grow much faster and bigger. CO2 is airborne plant food. Current slightly elevated levels of CO2 are increasing plant growth, biomass formation and crop yields. They are literally greening the planet. Matt Ridley in his excellent rebuttal of IPCC alarmism cites a figure of a 14% increase in greenery over the last 30 years, based on satellite observations.
If we look at climate negotiations over recent years, and at the rate at which the world is building coal-fired power stations, it is clear that any thought of reducing levels of atmospheric CO2 is simply fanciful. We cannot achieve it no matter how many billions we waste on wind farms. But the good news is first, that CO2 is not causing significant warming, and pace Al Gore is not a threat to humanity. And rising CO2 levels will have considerable benefits that Lord Stern and the IPCC have not considered.