The world's two biggest emitters of greenhouse gases are sparring on China questioning whether the U.S. can deliver on the landmark climate legislation signed into law by President Joe Biden this week. [Twitter] over climate policy, with “You can bet America will meet our commitments,” U.S. Ambassador to China Nicholas Burns tweeted in response on Wednesday, using a national flag emoticon for “America." He called on China to resume suspended climate talks, writing, “We're ready." The punchy exchange, part of a longer back and forth on Twitter, is emblematic of a broader worry: U.S.-China cooperation is widely considered vital to…