The Science of CO2

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Writes Luboš Motl,

Compare the changes of "CO2 as food" and "temperature change due to CO2" since the industrial revolution. The CO2 has increased by 40%. This allowed the plants to grow 20% larger or easier – the yields are some 20% different. It's not good just for the plants but for everyone who eats them or who eats the eaters etc. – it's ultimately all animals and humans who benefit, too.

On the other hand, the warming caused by the extra CO2 may be comparable to 1 °C measured by the thermometers – we're generous about the temperature change as well as about the assumption that all the change was due to the higher CO2 levels.

What makes a bigger impact: a 20% or 40% increase of your (plant's) "income", or a change of some hard to identify average by 1 °C? You know the answer, don't you? The 1 °C temperature difference is the difference between Boston and Providence, or whatever. Two nearby cities. There is no real difference. The difference between crop yields and "quality of life" dependent on the climate is surely smaller than 20% let alone 40%. The effect of higher CO2 as the "plant food" on the ecosystems is greater than the greenhouse effect by orders of magnitude – but it's still small enough that we usually ignore it.

(We shouldn't ignore it. If the CO2 dropped to 280 ppm again tomorrow, the crop yields could drop by those 20% again and 20% of the world population could get a bit hungry or some major adjustments to what we grow and eat would have to be made. It's the decrease of CO2 in the future which may be a problem, not the increase of CO2!)

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