BEIJING — A year and a half ago, negotiators from the United States persuaded the Chinese government to commit to a deadline for reversing the growth ingreenhouse gas emissions from China.

The Obama administration portrayed the pledge as a major victory because China produces more of the gases that cause global warming than any other country, a quarter of the world’s total. Though the deadline was far off, in 2030, environmentalists said the concession by Beijing was a significant breakthrough in efforts to coordinate a global response to climate change.

Now, some researchers examining recent energy data and the slowing Chinese economy are asking whether emissions of carbon dioxide, the main greenhouse gas, are already falling in China — more than a decade earlier than expected.