This week, the U.S. State Department released its 2014 Climate Action Report, explaining how the Obama administration plans to meet its official goal of cutting U.S. greenhouse-gas emissions 17 percent below 2005 levels by 2020. That's considered a first step toward further global efforts to address climate change.

Here's the key chart:

There's a lot going on here, so let's unpack this a bit:

1) U.S. emissions have already fallen in recent years. That's the dark blue line. Specifically, in 2011, U.S. greenhouse-gas emissions were 6.5 percent below 2005 levels, thanks to a combination of improved energy-efficiency, the recession, and the expansion of cleaner sources of electricity like natural gas and wind.

2) But emissions are expected to rise again soon. Now check out the dark blue projections at the top right. The Obama administration expects U.S. greenhouse-gas emissions to rebound between 2012 and 2020 if no additional policies are put in place. There's a range of uncertainty here, in part because total emissions are influenced by land use and changes in forest cover to sequester carbon (this is called "sequestration variability"). But the bottom line is: The United States basically can't meet its goals without further action.

3) With additional policies, the United States could get back down "in the range" of its 2020 climate goals. These are the green projections. The Obama administration thinks that it can get close to a 17 percent cut in emissions by 2020 with further measures. That includes the forthcoming carbon-dioxide regulations on existing power plants. It includes new regulations on methane emissions from natural gas operations. And it includes stricter energy-efficiency measures for a range of appliances and vehicles.

Notice that even with all these policies, it's not certain that the country will get to 17 percent below 2005 levels by 2020 (the dashed red line). A lot depends on how stringent the new regulations on coal- and gas-fired power plants are (this is "CAP variability"). The Environmental Protection Agency has a lot of leeway here in crafting rules. A lot depends on what sorts of regulations the Obama administration thinks will hold up in court.

Note that the United States will also need a bit of luck to get to that 17 percent reduction. Total emissions in 2020 will depend, again, on changes in land use and forestry that are hard to influence with policy. The Obama administration is basically hoping it can get close enough.

4) U.S. emissions are then set to rise again after 2020. This is an oft-neglected point. The Obama administration is aiming for reductions by 2020. But that's not nearly enough to avert a 2°C rise in temperatures, which is the broader goal. For that, all the world's major emitters would need to work together to keep cutting emissions sharply between now and 2050 and beyond. That entails a fairly rapid transition to cleaner sources of energy.

The United States isn't really on pace for that broader goal. Right now, the Obama administration is mostly relying on incremental progress to nudge emissions down. Replace a bunch of coal-fired electricity with natural gas. Tighten up some efficiency standards. Regulate power plants. But this isn't a permanent shift. The State Department report notes that U.S. greenhouse-gas emissions are expected to rise after 2020:

So the 2020 target is only a first, modest step for tackling climate change. The Obama administration is basically hoping that they can meet their interim emissions goals. Then they can turn around and use that success in future climate talks to convince other countries — including China and India — to do more to reduce their own emissions. And then they hope that new plans (or technologies) emerge to help keep reducing emissions between now and 2050. But for now, all of that is far from certain.

Related:

-- The IEA thinks we can still avoid 2°C of global warming. Here’s how.

-- The New York Times' Coral Davenport wrote a detailed piece yesterday on how the State Department has put a greater emphasis on climate change in recent months.