Tuesday, January 30, 2018

What are the effects of carbon dioxide in the atmosphere?

Apart from the obvious, or course.  Once, when our planet was young, the atmosphere was very high in carbon dioxide.  Then photosynthesis evolved and the cyanobacteria that spread across the oceans turned most of that carbon dioxide into oxygen about two and a half billion years ago.  Modern complex life, like ourselves, loves oxygen but for the creatures at the time this was a huge problem since oxygen was toxic to them and most of them died.  Plus the interruption of the greenhouse effect combined with the dimmer sun we had back then to turn Earth into a giant snowball for a bit.

But here we are billions of years later and carbon dioxide levels are increasing.  We should be worried about increasing temperatures but are there other reasons to worry?  For a very long time, compared to humanity, Earth's carbon dioxide levels were around 280 parts per million.  That's been going up recently and is now at 407 parts per million, a 45% increase.

If you are a photosynthesizing plant you might have complex feelings about this but if you're a mammal who really just wants to expel carbon dioxide from your lungs then there really isn't any upside.  We know that sufficiently high carbon dioxide concentrations will kill us but that takes  an atmosphere that's well above 10% carbon dioxide, 10,000 parts per million, very far from any levels we could plausibly reach by burning too much coal.  But some researchers have investigated the effect on people's cognitive abilities from going from 600 ppm to 1000 ppm and found easily measurable declines.  Now, poorly ventilated indoor spaces might easily get up to 2000 ppm so that's something to think about when designing office spaces.  But if a 400 ppm difference can result in obvious differences for people proofreading papers when briefly exposed can we be sure that there isn't some difference in human physiology that would stem from a 100 ppm difference across an entire childhood?  How about a 200 or 300 ppm difference?

This probably won't be a huge difference but it's not something that's been researched and not something you really could ethically research in humans.  But it is something that I think is underplayed in in our rhetoric about climate change.

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