Barack Obama has disappointed liberals on everything from civil liberties to health care to financial reform since taking office in 2009, and nowhere has he let his base down more than on climate change. The American Clean Energy and Security Act, a cap-and-trade bill that would have reduced carbon emissions by roughly the amount needed to avert catastrophe, passed the House in 2009 but was dead on arrival in the Senate.

And since the Tea Party wave of 2010, the White House has made no effort to bring another comprehensive bill to deal with the mounting problem before Congress.

So when discussing the Keystone XL pipeline in a new interview with Rolling Stone, the president tries to get at the obstacles (mostly a weak economy) that have made progress on the environment so difficult:

The reason that Keystone got so much attention is not because that particular pipeline is a make-or-break issue for climate change, but because those who have looked at the science of climate change are scared and concerned about a general lack of sufficient movement to deal with the problem. Frankly, I’m deeply concerned that internationally, we have not made as much progress as we need to make. Within the constraints of this Congress, we’ve tried to do a whole range of things, administratively, that are making a difference – doubling fuel-efficiency standards on cars is going to take a whole lot of carbon out of our atmosphere. We’re going to continue to push on energy efficiency, and renewable energy standards, and the promotion of green energy. But there is no doubt that we have a lot more work to do.

Part of the challenge over these past three years has been that people’s number-one priority is finding a job and paying the mortgage and dealing with high gas prices. In that environment, it’s been easy for the other side to pour millions of dollars into a campaign to debunk climate-change science. I suspect that over the next six months, this is going to be a debate that will become part of the campaign, and I will be very clear in voicing my belief that we’re going to have to take further steps to deal with climate change in a serious way. That there’s a way to do it that is entirely compatible with strong economic growth and job creation – that taking steps, for example, to retrofit buildings all across America with existing technologies will reduce our power usage by 15 or 20 percent. That’s an achievable goal, and we should be getting started now.

As much as small steps like postponing (and perhaps even cancelling) the Keystone pipeline make a difference, the president must refocus the debate on global warming in this campaign — and a second term — to be regarded as anything other than a failure on environmental issues.

In this interview we get a hint of how he might do that: by drawing attention to the villains (mostly big oil and other corporate interests) blocking progress.

But first he needs the economy to recover.