The greater the uncertainty about rising CO2's consequences, both in desireability and magnitude, the greater the need to control its emission (until there is greater certainty). For illustration, suppose it's 50/50 that rising CO2 is good/bad, and 50/50 those outcomes are modest/extreme. That's a 1 in 4 chance its very bad.
If you hear news that substance X is harmful to your health, but the industry creating X says it is not harmful, then you have uncertainty about X. Do you continue to consume X, or do you cut back a bit, at least for now, and try to learn more about it?
Edit: admittedly, when it comes to foods consumed, we've been dragged every which way over the past 40 years.