Now that Al Gore and the Intergovernmental Panel on Climate Change have won the 2007 Nobel Peace Prize, will the US Congress take the IPCC’s scientific advice on how to fight global warming? The IPCC holds that the world must reduce greenhouse gas emissions at least 80 percent by the year 2050. Few in Congress seem prepared to go that far, however. And judging from the discussion at a closed-door meeting on Capitol Hill last week, even lawmakers who personally embrace the “gold standard” of 80 percent reductions are prepared to endorse a weaker measure in the name of getting some form of climate legislation moving in Congress.

“Don’t let the perfect be the enemy of the good.” So goes one of the oldest sayings in politics, generally invoked by reformers who think that half a loaf of progress is better than none. Often the reformers agree privately with more ambitious colleagues who want the entire loaf, but they argue that pushing too hard and too soon may end up yielding no progress at all.

There are times when this is sound strategic advice. Is the current battle over global warming legislation one of those times?

The terrain of the battlefield has changed considerably over the past year. For a variety of reasons–including the Democratic takeover of Congress in 2006, the alarming series of reports the IPCC has issued in 2007 and the news pouring in from the front lines of climate change (scientists recently projected that Arctic summers will be ice-free by 2030, thirty years earlier than their previous “worst-case” projection)–global warming legislation finally is getting a hearing on Capitol Hill. There is even a decent chance that Congress might pass a bill, though President Bush seems certain to veto anything that goes beyond his repeatedly stated insistence on purely voluntary measures.

The question is, what bill will reformers get behind? How ambitious will they be? Will they demand what the scientific community says is the minimum necessary to enable our civilization to (perhaps) avoid the worst future scenarios of global warming: deep cuts in emissions by 2020 on the way to 80-90 percent cuts by 2050? Or, in the name of not letting the perfect be the enemy of the good, will they favor a more modest and gradual approach?

The latter, incrementalist strategy has the upper hand at the moment. The vehicle is a bill that will be sponsored by Senators Joseph Lieberman, Independent of Connecticut, and John Warner, Republican of Virginia. The bill is still taking final shape, but its key provisions reportedly include a 10 percent mandatory reduction in emissions by 2020 and 70 percent by 2050.

Not only do these provisions fall short of the scientific standard; there is even less here than meets the eye. The bill, as described in briefings and press accounts, contains a number of loopholes, including provisions that (1) will give rather than sell greenhouse-gas-emissions permits to polluters, thus violating the “polluter pays” principle of environmental accounting, and (2) count so-called carbon offsets–that is, paying someone else to reduce emissions while continuing to emit oneself–as genuine reductions.

An alternative approach, sponsored by Senators Barbara Boxer, Democrat of California, and Bernie Sanders, Independent of Vermont, comes much closer to the scientific consensus. The Boxer-Sanders bill (like a similar measure sponsored in the House by California Democrat Henry Waxman) calls for mandatory 80 percent reductions by 2050 and stipulates that they be real reductions; i.e., not just carbon offsets. The Boxer-Sanders bill also would uphold the “polluter pays” principle by selling emissions permits rather than giving them away.

[For a description of these and other pending global warming bills, see the World Resources Institute’s analysis here.]

Guess which bill is getting traction and support on Capitol Hill?

According to sources speaking on background because of the confidential nature of the discussions, most Senate Democrats and many environmental and other public interest groups are preparing to support the Lieberman-Warner bill, despite misgivings about its shortcomings. At a closed-door meeting on Capitol Hill last week attended by more than a dozen key Democratic senators and scores of leaders from the environmental and larger public-interest community, participants were urged to fall into line behind the Lieberman-Warner bill because it was the most likely to secure bipartisan support and perhaps pass. Activists who pointed out the flaws in the bill were told by a number of senators, allegedly including Boxer herself, to work to improve the bill as it moved through the legislative process, rather than oppose it.

In other words, don’t let the perfect be the enemy of the good.

Asked to comment about her role at the meeting, Senator Boxer told The Nation, “I believe it is critically important that we get started now on legislation that will prevent dangerous climate change. And I will continue to work on this issue until that goal is achieved.”

Activists who feel otherwise fear that the Lieberman-Warner bill will become the defining benchmark for future federal action on climate change. Author and journalist Bill McKibben, who did not attend the Capitol Hill meeting, was quoted to this effect in this Nation report two weeks ago:

“We are really playing for the opening months of 2009 here,” said McKibben, adding that it would be better for the current Congress to pass nothing than to approve a weak bill, because a weak bill would lower the bar for the next Congress and President and deflate pressure for reform by giving people the impression that the problem has been solved: “Since Bush is going to veto it anyway, there is no reason to make [a bill] less ambitious than what science requires. Climate change isn’t like other issues. It doesn’t do any good to split the difference to reach a deal everyone can live with. Climate change is about the laws of physics and chemistry, and they don’t give.”

Commenting for this article, a senior aide to Senator Boxer said that both sides of the good versus perfect divide “want to get to the same place.” And this was possible, the aide further argued, if proponents focused less on the specific target of 80 percent cuts and more on ensuring that federal action always be guided by the best science available. “Global warming legislation needs to require that the best science be reviewed regularly to ensure that the emissions targets in the bill are sufficiently strict to prevent dangerous climate change,” said the aide. Senator Boxer has publicly urged that the legislation include what she calls “look-backs,” requirements that federal agencies continue to monitor scientific developments on climate change, then “look back” and tighten federal standards, if necessary.

If such a bill does pass Congress, it would confront the White House with a difficult choice. President Bush is now on record saying that climate change is a serious problem, humans are causing it and action must be taken. Meanwhile, global warming is shaping up as one of the top-tier issues in the 2008 campaign. Bush presumably will not want to sign a bill that would lead to mandatory emissions reductions, which both the “perfect” and the “good” approaches outlined above would certainly do. At the same time, a presidential veto of a scientifically sound global warming bill carries risks for fellow Republicans, especially once they leave their party’s primaries behind for the general election campaign. Given Bush’s record–his recent veto of health insurance for kids and his general bull-headedness on Iraq–a veto seems the most likely outcome. But only if Congress puts a bill on his desk in the first place.