The topic of CDR is linked to the broader discussion of climate change/global warming. If you aren’t convinced that our planet is heating up due to humans burning fossil fuels it is difficult to see the need for CDR.
While we try not to get into heated discussions with climate change deniers, it pays to quickly mention the most frequent arguments by deniers and skeptics so we can be prepared to answer.
Plants need CO2 to grow and - within limits - more of it, everything else being equal, is better for their growth.
However, plants need more than CO2 to grow. If critical minerals are in short supply - which they often are, they can’t grow more even if there is plenty CO2 available.
This argument is like saying: humans need calcium to grow and therefore all we need to eat is ice cream, because it has a lot of calcium.
Also, plants, just like humans and animals, are adapted to a certain climate. Heat and drought can hinder their growth.
Plants are part of a complex ecosystem and just increasing one component, even an important one, does not make up for the disruption of ecosystems due to heat, drought, or floods.
This argument is based on the misunderstanding that the goal of CDR is to remove all CO2 from the air, which, of course, it isn’t. The goal is to restore CO2 to pre-industrial revolution levels when the atmosphere was healthier.
CO2 concentrations were indeed much higher in distant history. The last time they were as high as they are now, was over 3 million years ago. Humans had not evolved yet.
Humans evolved later and with the beginning of the Holocene period about 12,000 years ago started thriving. Most significant advancements, such as agriculture, happened during the Holocene, a time of a stable warm climate. The CO2 concentration in the air was around 250 - 300 ppm. These are the conditions for which modern humans (and our ecosystems) are adapted. By increasing the CO2 concentration, as we have, we are altering the climate and are falling out of the beneficial conditions of the Holocene that made rapid human development possible in the first place.
Some people go as far as saying that we should have 800 - 1000 ppm CO2 concentrations that we haven’t had in more than 50 million years. This would take us back to the super hot and very humid Eocene when the first primitive mammals walked the earth.
In short, a warmer planet with higher CO2 concentrations certainly existed in the earth’s history. However, humans thrived during lower heat/lower CO2 concentration and are adapted to the lower temperatures we have enjoyed during the Holocene period.
Methane is a powerful greenhouse gas, It has far greater heat-trapping capabilities than CO2. However, it is much less stable is disappears from the atmosphere must faster than CO2 (i.e., in decades rather than centuries).
Methane reduction in the near term is very important. However, CO2 reduction is critical for the near and long term.
Water vapor also is a powerful greenhouse gas but higher CO2 levels make the effects of water vapor worse.
Here is how it works: warm air can hold more water. So, a warming atmosphere (due to more greenhouse gases) holds more water which then makes the warming worse. This is known as a positive feedback loop.
If we decrease CO2 and methane concentrations, temperatures will fall, the air will be able to hold less water vapor, and decreased water will help further reduce the temperature.
The average warming of 1.2 degrees Celsius doesn’t sound so bad. But an average temperature doesn’t tell the whole story.
Some areas, such as the North Pole, Greenland, and Siberia are heating up much faster. Temperature increases over the next 50 years could leave between one to three billion people stranded in places that are hotter than just about anywhere on Earth today — and far outside the band of temperatures that humans have weathered for at least the past 6,000 years. Neither fauna nor flora in these places are adjusted to these temperatures and could face mass extinction.