The network is complete enough to give a clear picture of the overall global trends in industrial gases in the air, scientists say. But it is too sparse to give definitive information about which parts of the planet are absorbing or releasing greenhouse gases at a given moment. Lacking such data, scientists have trouble resolving some important questions, like the reasons for the rapid increase of carbon dioxide over the past three years.
“It’s really important that people get that there’s an awful lot that’s just not known yet,” Sam Cleland, the manager of the Cape Grim station, said.
Human activity is estimated to be pumping almost 40 billion tons of carbon dioxide into the air every year, an amount that Dr. Canadell of the Global Carbon Project called “staggering.” The atmospheric concentration of the gas has risen by about 43 percent since the Industrial Revolution.
That, in turn, has warmed the Earth by around 2 degrees Fahrenheit, a large number for the surface of an entire planet.
With a better monitoring network, scientists say they might be able to specify in greater detail what is causing variations in the amount of carbon dioxide staying in the air — and, perhaps, to give a timely warning if they detect a permanent shift in the ability of the natural sponges to absorb more.
Dr. Tans of NOAA would like to put sensors on perhaps a hundred commercial airplanes to get a clearer picture of what is happening just above land in the United States. The effort would cost some $20 million a year, but the government has not financed the project.
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.
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