>If it turns out to be incorrect there's no harm is there? It's not like we can overreact to climate change.

We can. Human life is still resource constrained. While we live better lives than ever before, it's something that can always improve. The resources we spend on dealing with climate change could've been used to improve the lives of people instead. An investment in the economy today can have (positive) compounding effects in the future.

We could live like people lived in the middle ages, but that would cause more human suffering than it would help. The same point goes for the future though - if we stop technological advancement, then how many people will suffer from issues of the modern day that would be solved in the future?

Ultimately, it's a balancing act on what will help more people more in the long run.

Of course we can, ban fossil fuels overnight and nuke everyone who doesn't comply, nuclear winters are good against global warming. Reducing carbon emissions is tame as far as possible responses go, there are some extreme solutions involving geoengineering.

It won't happen because there are more incentives for underreacting than overreacting but yes, definitely possible.

The harm in being incorrect is that more and more people will use the past incorrect statements as grounds to dismiss future potentially correct statements.