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How much it costs to cut 1 metric ton of carbon emission with various methods for different global carbon emission levels
(www.edf.org)
As you reduce the amount of carbon emissions (the y axis) the methods to keep reducing carbon cost more (the x axis.)
This great graph came to my attention from this video from vlogbrothers. It also has some good explanations of what it means.
Note that carbon capture doesn't really make sense till you've exhausted all the other emission minimizing methods.
Source: https://www.edf.org/revamped-cost-curve-reaching-net-zero-emissions
Let's say that for millions of years a healthy biosphere grew around forests and the balance worked. Now you come to tell us it doesn't. Wouldn't you think it's a bit unconvincing?
We've only been pumping out co2 for a hundred or two years. We can't keep doing that and expect the old balance to hold up.