What is the ideal level of CO2 in the atmosphere?
As CO2 is essential for life on Earth, we need enough of it.
Not enough of it, and our food supply fails.
Too much, and global warming will continue unrestricted.
What is the ideal amount?
There are conflicting requirements and constraints on CO2. We need to take them all into account.
How much CO2 is enough?
Here is a typical misleading post from John Shewchuk.
In it he says that CO2 levels are getting dangerously low. He shows higher levels from millions of years ago - way before the time of humans - and hides human times as a tiny "dot".
The truth is that humanity has never experienced CO2 levels higher than now. Human civilization has developed with fairly steady levels for many thousands of years, growing more and more food and thriving. But from the second half of the 19th century CO2 levels started to increase, and that rate of increase has increased sharply.
So in fact, CO2 levels are higher now than they have ever been during mankind's existence. And CO2 levels are still rising rapidly.
Why does John Shewchuk claim that they are dangerously low - we are in a "CO2 famine" - when mankind has never experienced such high levels before?
Is more CO2 always better for plant growth?
There have been many studies to try to establish ideal levels of atmospheric CO2 for plant growth.
Here is one that points out there are several factors to take into account, including:
- Although higher levels of CO2 generally benefit photosynthesis, the process also requires other resources, including nutrients. Potential gains will not be realised if these other resources do not "keep pace"
- The warming effect of elevated levels of CO2 introduces other negative growth factors, including drought and heat stress
- Weeds may also benefit from the elevated CO2
- Food grown under conditions of elevated CO2 becomes less nutritious, losing significant amounts of iron and zinc.
To some extent many of these issues can be addressed when growing food in a controlled environment such as a greenhouse. Many growers raise the level of CO2 in their greenhouses. But that approach only works in enclosed and controlled enviroments. For food which is grown outdoors (which most of our food is) those issues are signficant.
Climate change’s negative effects on plants will likely outweigh any gains from elevated atmospheric carbon dioxide levels.
What is the ideal level of atmospheric CO2?
This is another question which has been widely addressed recently.
On this MIT Climate Portal page the issues raised above are covered, but the writer also makes this point:
We know from the geologic record that hundreds of millions of years ago, Earth had an atmospheric CO2 level in excess of 2,000 parts per million (ppm). That’s compared to around 280 ppm in pre-industrial times and 417 ppm in 2022.
Although plenty of plants lived through that period — albeit different species and in different places than today — humans did not. Such a CO2 level would produce year-round scorching temperatures akin to what we experience in summer today. In other words, he says, “this is not a period we would ever want to visit.”
Another MIT Climate Portal page summarizes the results of research with this:
Atmospheric CO2 levels of between 280 and 350 parts per million created the climate that let humanity build and feed the modern world. The farther we get from those levels, the more we run the risk of disturbing that balance.
We have already disturbed the balance by exceeding those levels, and are continuing to do so.