The Coronavirus and Carbon Emissions

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In the past month, the world has seen a remarkably large drop in emissions of carbon dioxide, the main driver of global warming. The reason isn’t something to celebrate, though.

The coronavirus outbreak in China, which has sickened at least 80,000 people, has shut down factories, refineries and flights across the country as officials order people to stay home. As a result, China’s carbon dioxide emissions over the past three weeks have been about 25 percent lower than during the same period last year, according to calculations by Lauri Myllyvirta, an analyst at the Center for Research on Energy and Clean Air.

China is such a huge industrial polluter that even a temporary dip like this is significant: The three-week decline is roughly equal to the amount of carbon dioxide that the state of New York puts out in a full year (about 150 million metric tons) Mr. Myllyvirta estimated.

The numbers offer a sobering reminder of how deeply the modern economy still depends on fossil fuels. Whenever industrial activity declines, whether because of a recession or a major disease outbreak, climate pollution tends to plummet, too.

You can see the drop in China’s coal consumption in the chart above. Every year, the nation’s coal use falls during the weeklong holiday around the Lunar New Year, which occurred on Jan. 25 this year. Coal-burning emissions then typically rise again once people return to work and factories spring back to life.

But this year, coal use has yet to rebound. In late January, the Chinese authorities extended the New Year’s holiday and restricted travel and public gatherings in an attempt to stop the coronavirus from spreading.

The effects have rippled through virtually all sectors of China’s economy.

Construction activity has slowed, which has meant reduced demand for steel and other materials. Oil refineries are producing less fuel than usual as cargo trucks sit idle and the number of flights has dropped by about 13,000 per day. Activity in key industrial sectors has declined by 15 percent to 40 percent over the last three weeks compared with the previous year. (Mr. Myllyvirta first published his analysis at Carbon Brief last week and on Tuesday updated it with another week of data.)

But economic disruptions on this scale, whether caused by disease or recession, are usually accompanied by severe human costs and rarely make it easier to fight climate change. In some cases, they can make it harder.

For one thing, it’s likely that China’s emissions will quickly rebound when the outbreak is finally contained. Li Shuo, a senior policy adviser for Greenpeace Asia, said that in the past, China’s factories have tended to ramp up production to make up for lost output or temporary shutdowns, a practice he calls “retaliatory pollution.”

Mr. Li warned that the outbreak could even hinder China’s continuing efforts to green its economy and try to tackle climate change. The Chinese government has set ambitious targets for economic growth this year and will now have to race to make up for lost time. That may mean new policies to stimulate polluting industries like steel and cement, or a relaxation of efforts to shift away from coal.

“Controlling the outbreak and maintaining economic growth are now going to be China’s top priority,” Mr. Li said. “And we’ve seen in the past, whenever economic growth needs to be prioritized, the environmental agenda takes a back seat.”

A controversial idea to fight climate change by using iron to manipulate ocean ecosystems probably won’t work, according to a study by researchers at the Massachusetts Institute of Technology.

The study, which was based on computer modeling and published this month in Proceedings of the National Academy of Sciences, looked at adding iron to the oceans as a sort of fertilizer for phytoplankton, the tiny plants and algae that can absorb planet-warming carbon dioxide from the atmosphere.

The researchers’ finding: The world’s oceans appear to have all the iron they need, thank you.

“Iron fertilization cannot have a significant overall effect on the amount of carbon in the ocean because the total amount of iron that microbes need is already just right,” said Jonathan Lauderdale, a research scientist in the university’s department of earth, atmospheric and planetary sciences and the study’s lead author.

David Emerson, a senior research scientist at the Bigelow Laboratory for Ocean Science in East Boothbay, Maine, said the study raised important questions about iron fertilization and its effects.

“The authors of this PNAS paper point out an important potential shortcoming of long-term iron fertilization based on computer model simulations, and these cannot be taken lightly,” he said.

Dr. Emerson said the concept of iron fertilization required more research that would take “at least one to two decades of work and expenditures in the low billions of dollars.”

Phytoplankton, which uses carbon dioxide for photosynthesis, needs iron to grow. So adding more iron to the oceans, the theory goes, would lead to more phytoplankton and more carbon being pulled from the atmosphere.

The theory, and the field of geoengineering in general, is contentious because many scientists and environmentalists fear that large-scale manipulation of ecosystems could come with large-scale unintended consequences.

In the summer of 2012, George Russ, an American businessman, sprinkled 100 tons of iron dust into the Pacific Ocean off the coast of British Columbia in an ecological venture that outraged scientists and government officials in both Canada and the United States.

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