One question that often comes up about my novel Diamond Tide is (mild spoilers to follow), “How can reducing the pollutant carbon dioxide be a bad thing?”
One might equivalently ask, “What is the optimum level of atmospheric CO2?” If one browses the current political rhetoric, news media, or the climate science literature after 1980, it’s plain that more atmospheric CO2 is bad. Imagine for a moment that there was a way to dial back CO2 – a knob with which to set the level. Where should it be set?
OK, that’s the wrong question. Angst about CO2 is really angst about temperature. In theory and in the computer models based on that theory, increasing atmospheric CO2 will mean increasing global temperatures. So instead imagine that the knob controlled global temperature. What’s the perfect global temperature at which to set that knob? The temperature in 1980 before global warming became a concern? Early 20th century, before the ongoing carbon fuelled industrial revolution? The warm medieval when Greenland was being farmed and northern England was wine country? The cool 17th century when glaciers advanced and European crops froze in the fields?
If you own a marginal ski resort with a short and unpredictable snow season, you’ll probably want the temperature taken down a few degrees from where it is now. If you range cattle in the northern Sahel, you might agree. But if you’re a farmer trying to eek out a living in the short growing season of Siberia, you’ll want the temperature up, not down. Likewise for an Irish seaside resort owner. It really depends where on Earth you are and what you hope for when you look at the weather forecast.
As Charles Dudley Warner famously pointed out, “Everybody complains about the weather, but nobody does anything about it.” That may be for the best. There would be no better agreement on the one perfect global temperature, than there would on the one perfect appetizer. If such a knob did exist, it would have to be kept under armed guard.
Suppose, for a moment, that we could uncouple temperature from CO2 – give CO2 its own knob while the rabble argued about temperature. There are reasons why more CO2 would be better. Without question, plants grow faster and bigger with more CO2 (other factors being equal), because CO2 is what plants eat. They are made almost entirely from CO2 and water – the nutrients they draw from the ground are mere condiments.
A doubling of the current (400ish ppm) CO2 level could both increase plant growth by around 50% and decrease their need for water. This would be a boon for both crops and rainforests. Throughout most of the history of life on Earth, CO2 has been four to ten times what it is today. We are in an austere period, CO2-wise.
That’s not to say that returning to those golden days of thick CO2 would have a salubrious effect on crops. The plants that are with us today have evolved over a million years of ice ages, during which CO2 rarely has risen above current levels but often has plummeted to dangerous lows. They are adapted to cope with the (geologically) recent CO2 scarcity. They may need a good deal of evolution time before they could embrace CO2 levels at ten times what they are now.
This brings us to the question, “What would happen if CO2 were to fall?” The present ice age, which has been going on for over a million years, is marked by periods of glaciation lasting around 100,000 years, when ice sheets cover much of the northern and southern land masses. These cold periods are separated by brief warm periods, such as we have enjoyed for the past 10,000 years. During the cold glaciations, CO2 sometimes drops to less than half what it is now. While plants can survive cold by retreating toward the equator – the ice sheets never extend to the tropics – they cannot escape the worldwide paucity of CO2. All plants alive today have survived CO2 as low as 160 ppm.
In laboratory tests, these low CO2 levels reduce plant growth by about half current. Cutting CO2 to a fifth of what it is now can be fatal. The present CO2 level appears to be on a linear part of the curve of growth versus CO2. Any foreseeable rise in CO2 will monotonically increase crop yields, and any decrease will lower yields. Thus, we can expect increasing yields and better nutrition worldwide in coming decades. On the other hand, if we were able to dial back CO2 to pre-industrial levels, food production worldwide would drop. We can presently feed seven billion people. Even a 10% drop in food production would be the equivalent of 700,000,000 people (seven hundred million – twice the population of the US) going without food. The nutrition of seven billion people is critically dependent on keeping CO2 at or above its current level.
In Diamond Tide, CO2 falls precipitously for reason one would have to read the novel to understand. Maybe not even then. The result is not good for Man.
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