Back in 2009, at the global climate talks in Copenhagen, the United States promised to cut its greenhouse-gas emissions 17 percent below 2005 levels by 2020. The conventional wisdom is that there’s no way we can possibly hit that target, especially after the Senate killed a cap-and-trade bill last year. But David Hone, the climate change adviser for Shell*, has a worthwhile analysis suggesting that the combination of the steep recession, new EPA rules on power plants, and low natural-gas prices might actually let us meet those goals, after all. Here’s the chart:

Now the caveats. There’s a lot of uncertainty in these projections. The U.S. economy could recover far more quickly than expected, which would cause emissions to rise. Congress or a new president could block those EPA rules. Automakers could find wiggle room in the fuel-economy standards. Hone also seems fairly optimistic about biofuels — plenty of analyses have suggested that corn ethanol can inflict more damage to the atmosphere than plain old gasoline, once you account for the way they spur deforestation. Meanwhile, Hone has left out any likely effects from the EPA’s forthcoming rules on greenhouse gases, although many experts are no longer expecting much there, apart from spurring modest efficiency upgrades at power plants and refineries.

So when you hear people like U.S. Ambassador to Australia Jeff Bleich say that it’s “absolutely realistic” for the United States to meet its Copenhagen goals, this is the reasoning. But, on the other hand, the United States isn’t putting itself on a sustainable path for the sorts of big cuts in carbon pollution that scientists say are necessary to avoid dramatic climate change. We’re relying on one-off events like a financial crash and a wave of power-plant closures. That’s quite different from a sweeping transformation of our energy sector.

* Yep, Shell does indeed have a climate adviser. It’s a major oil company that tentatively supported the cap-and-trade bill the Senate mulled over last year. Make of that what you will.