There is almost certainly a point where the costs of massive planet-scale intervention outweigh the costs of doing nothing. I'm not sure exactly where that point lies, but I'd guess it's somewhere between Solar Radiation Management (SRM) and glacial geoengineering projects like the one in this article.

The question in my mind is not whether or not to fund these efforts (we will need to), but how to fund them quickly enough.

There aren't many investment vehicles that are truly global in scope. We've seen individual nations do incredible things when they stand to benefit. The Delta Works project in the Netherlands comes to mind, as does the Three Gorges Dam in China.

But how do we source capital when the whole planet stands to benefit? Especially when many nations either don't have the money and/or the political will. The scale of the problem far outstrips what charity or nonprofits can provide, and private companies can only do so much without a functional market.

I don't mean to suggest that this is an intractable problem. It really isn't-- There have been some really interesting financial innovations already. But we need way more attention on this stuff from the investment class. The bankers, fund managers, and policymakers that work in global development need to get creative, and fast.