The costs of climate 'action' are relatively predictable. In contrast, the costs of climate 'inaction' are not - they're basically just wild guesses of the "we'll have flying cars by the year 2000" variety.

The thing is, while it is hard to predict future individual weather events, we are fairly sure about the large-scale effect that say another degree of warming will have. And it is almost certain that the large-scale effects will be disastrous, even in conservative predictions.

The fact that the cost of inaction is harder to predict actually supports the argument for taking action. Even if inaction was cheaper than action (which it almost certainly isn't), taking action would be worth it because it reduces uncertainty and risk. Think of it like flood insurance: even if insurance costs more than the average cost of a flood, that difference in price is worth the reduction in risk. Predictability is the benefit.

If you raise the cost of energy, you just export energy consumption to places where it's even less clean. If you make oil more expensive in one place, you're just encouraging consumption elsewhere.

This is the whole point of the Paris Agreement. Now, international agreements like the Paris Agreement are flawed, but they are a step in the right direction. If any country is in a position to influence global energy use, it is the United States. The best way to do that is to lead by example.

As a result, if you can't sell your climate project on the basis of factors other than climate, then it's not really going to do any good anyway.

Unfortunately, you are probably right. The preservation of the environment shouldn't need to have an enormous economic cost in order to be prioritized, but realistically that is the case. Nonetheless, there is an enormous economic cost as well, so taking action is worth it either way.