The uncertainty stemming from the recent increases in carbon dioxide is all the more acute given that global emissions from human activity seem to have stabilized over the past three years. That is primarily because of changes in China, the largest polluter, where an economic slowdown has coincided with a conscious effort to cut emissions.
“I’d estimate that we are about at the emissions peak, or if there are further rises, they won’t be much,” said Wang Yi, a professor at the Chinese Academy of Sciences in Beijing, who also belongs to the national legislature and advises the government on climate policy.
Emissions in the United States, the second-largest polluter after China, have also been relatively flat, but Mr. Trump has started tearing up President Barack Obama’s climate policies, raising the possibility that greenhouse gases could rise in coming years.
Dr. Tans said that if global emissions flattened out at today’s high level, the world would still be in grave trouble.
“If emissions were to stay flat for the next two decades, which could be called an achievement in some sense, it’s terrible for the climate problem,” he said.
