Backgrounder: Arguments for dealing with climate change deniers

We are trying not to get too deeply into it with climate change deniers. It is often a waste of time and generally doesn’t result - especially on social media - in a productive discussion.
Nevertheless, sometimes in the context of talking about CDR, one encounters deniers who argue that no CDR is necessary because no global warming exists.
They use a few of the same arguments in different versions. Here is some information about those that are relevant in the context of CDR.

Plants need CO2, the more the better

Picture source: Unsplash, Md. Hasanuzzaman Himel

This is an argument people seem to actually believe (rather than just use as an excuse): plants need CO2 and more of it is better for growth. This is why greenhouses artificially increase the concentration of CO2 to 800 - 1500 ppm.

The source below explains why this is an oversimplification and logical fallacy quite well, but in short:
too much of a good thing can be a bad thing and only focussing on CO2 as “plant food” neglects to take other important factors (water, other nutrients, etc. into account.

Source: More CO2 in the atmosphere hurts key plants and crops more than it helps