"The US pledge: As part of the bargain, the US government has pledged to reduce emissions 26 to 28 percent below 2005 levels by 2025. This is a new and significant extension of the Obama administration's existing goal to reduce emissions 17 percent by 2020.
The biggest question here is whether US policymakers will actually follow through on this pledge. The country's carbon-dioxide emissions are currently 10 percent below 2005 levels, but they've started to rise again of late. The US Environmental Protection Agency has proposed new rules to curb emissions from existing power plants, but that's unlikely to be enough to achieve a 28 percent cut. So where will additional policies come from? Note that Congress is deadlocked on climate, with many Republicans furious about this new deal.
The China pledge: For the first time ever, China has set a goal of having emissions stop growing by 'around' 2030 — and possibly earlier. China will also aim to get 20 percent of its energy from non-fossil sources by 2030. (China isn't reducing its emissions as quickly as the US; the logic is that this is fair since China is still poorer.)"