At last, we're going to get to see the climate bill. After endless delays and petty mishaps, John Kerry and Joe Lieberman are set to release the American Power Act this afternoon. Here's a leaked summary of the bill, and here's a section-by-section rundown. The overall idea is simple enough: cut carbon pollution 80 percent by 2050 while cranking up the growth of cleaner alternative energy sources. But, of course, nothing's ever so straightforward and there are all sorts of questions to ask. Like: Is this sucker worth passing?

Depends on who you ask. A little while ago I ran through some of the rumored details of the bill and noted that, all told, it's pretty industry friendly. There are lots of provisions to soften the burden on oil companies, there's money to ensure that coal has a future (even though coal with carbon sequestration is a highly uncertain prospect), and the legislation gives industrial polluters a free pass until 2016 before they face regulation. Plus, the carbon reduction targets for 2020 are weaker than they could be.

Combine that with subsidies for nuclear power and an expansion of offshore drilling, and it's hardly a shock that we're now seeing some 200 groups on the left come out against the Kerry-Lieberman bill. In the eyes of many environmentalists, this bill may be worse than doing nothing—it won't shut down dirty coal plants and it will divert valuable resources toward despised technologies like new nuclear reactors. (Granted, that still leaves the question of what we should do instead to tackle climate change—rely on the EPA? Here's a rundown of how that Plan B would work.)

I have a somewhat more mixed view on the matter. It's true, the Kerry-Lieberman bill as written almost certainly isn't the optimal path for cutting U.S. greenhouse-gas emissions as quickly and cheaply as possible. The logic of getting 60 votes in the Senate sort of dictates that whatever legislation emerges from that chamber is going to be deeply—even horribly—flawed. But putting even a small price on carbon and beginning the process of nudging industries toward efficiency and clean power is an important step.

Looking back through U.S. history, two things always seem to be true of green legislation. The first is that curbing pollution always turns out to be far easier and cheaper than anyone predicted. The second is that environmental regulations do get strengthened over time. The Clean Air Act was shabby and loophole-ridden when it was first enacted in 1963, but Congress steadily improved it over the years when inadequacies were found and after fears that the bill would wreck the economy proved unfounded.

And I do think the same dynamic will hold true of climate legislation. Once even a modest price on CO2 is in place, companies will start finding ways to save energy and cut emissions and find that it's remarkably cheap and easy to do so. Just as an example, check out this McKinsey study and note that there are hundreds of billions of dollars worth of efficiency savings in this country that are there for the taking—these are opportunities to cut carbon pollution at negative cost. And, as a result, Congress will find it easy to strengthen a bill over time. Putting a new law on the books is tough. Tweaking those rules over time is easier. And, while passing a climate bill in the few months before Democrats get slaughtered at the midterms looks extremely difficult, this may be the last chance to do so for a long, long time.