Environmentalists have had two tough pills to swallow over the last few weeks.

First, there was the news about the potential downsides of nuclear retirements, and second, the idea that it might be a good idea to start building dams again. Typically classical environmentalism and climate activism are mostly on the same page, but in some cases, there is real tension.

Let's take them in turn. Brad Plumer at Vox has a pretty good look at the nuclear situation:

...the US nuclear fleet is aging — and many plants need repairs and costly maintenance. In recent years, some merchant generators have decided that they can't sell electricity at high enough prices to pay for those repairs. So, they've decided to retire their reactors…what happens when a nuclear power plant gets retired? It depends on the region. But one recent study of a shuttered nuclear plant in California found that greenhouse-gas emissions surged, as the nuclear plant got replaced by fossil fuels. [Vox]

So, nuclear is being squeezed by cheap power from natural gas and (increasingly) renewables on one side, and the utter disaster that is U.S. infrastructure costs on the other side.

That latter point about infrastructure costs is particularly important, to my mind. Any comprehensive climate plan will necessarily involve Herculean construction projects in the aggregate, since it will have to include (at a minimum) totally overhauling our electricity distribution system. But right now, the U.S. is plagued by bloated infrastructure construction costs, especially when compared to similar countries. Since ridiculously overpriced building costs will make a serious climate effort that much more difficult, any plan has to involve dealing with this construction problem.

Now, here's where it gets tricky: Nuclear power plants are some of the most complicated structures ever built, so nuclear power may become much more competitive if they become cheaper to build and maintain. That means any energy plan that tackles infrastructure costs (which is, again, a necessity) probably will have the unintentional effect of making nuclear competitive, especially if combined with a carbon tax.

Would that really be a problem, though? While it has some inherent problems, nuclear power is relatively clean, and the amount of energy available so huge that if it turns out to be cost efficient, we probably just can't afford to rule it out. In any case, in the short term, any retirement of a plant that is already built should be avoided where possible. Even if we eventually shut down our nuclear capacity, that should be done after all carbon power is gone, not before.

Second, hydropower.

The Department of Energy released a report on this just a few days ago looking at potential new hydropower development. They divided this into two sections.

First, building on older work, they looked at existing dams and water control structures that don't generate any energy at all [pdf]. Yes, it turns out that there are 80,000 such things, the energy equivalent of 12 gigawatts of carbon-free capacity just lying around for the taking. The very fact that we haven't already built out every single one of those is just an awful policy failure.

More contentiously, the other part of the report finds that even if we start by excluding all federally protected lands (national parks and so forth), there are 65 gigawatts worth of potential new capacity that we could build on rivers, lakes, etc, which would just about double current US hydropower capacity. Given the stupendous waste and environmental devastation of the 20th century orgy of dam-building detailed in Marc Reisner's Cadillac Desert, that's going to be a fraught proposal. And doubly so because in many places, like the Southwest, water is clearly going to be a more critically important resource than power. Other considerations, including the beauty of the wilderness, are definitely going to require careful consideration when we're talking about something as high-impact as dams. (Drowning the Grand Canyon like China's Three Gorges, just for an example, would be completely out of bounds.)

But the bottom line is that when it comes to climate change, we really will need an "all of the above" strategy, only, contra President Obama, one that includes only carbon-free solutions. I wouldn't automatically greenlight anything and everything with zero emissions, but I also don't think we can afford to write off any carbon-free power sources when we're thinking about climate policy. Everything with the potential to make a dent in coal's share of electricity generation ought to get thorough consideration.