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| China’s Carbon Dioxide Emissions May Have Been Overstated by More Than 10% | China’s Carbon Dioxide Emissions May Have Been Overstated by More Than 10% |
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| HONG KONG — Scientists may have been overestimating China’s emissions of carbon dioxide, the main greenhouse gas driving global warming, by more than 10 percent, because of inaccurate assumptions about the country’s coal-burning, according to a study published on Wednesday. | |
| The study’s finding, published in the journal Nature, does not mean that the total level of greenhouse gases in the atmosphere is any lower than scientists had thought. That accumulation is measured independently. Rather, the finding may affect discussions of how much responsibility China bears for global warming, compared with other nations. | The study’s finding, published in the journal Nature, does not mean that the total level of greenhouse gases in the atmosphere is any lower than scientists had thought. That accumulation is measured independently. Rather, the finding may affect discussions of how much responsibility China bears for global warming, compared with other nations. |
| “This doesn’t change the fact that China is still the largest emitter in the world,” said Dabo Guan, a professor of climate-change economics at the University of East Anglia in England who is one of the paper’s two dozen authors, in a telephone interview from Beijing. “But it shows we need to know a more accurate base line for emissions, not only for China but also for the other emissions giants.” | “This doesn’t change the fact that China is still the largest emitter in the world,” said Dabo Guan, a professor of climate-change economics at the University of East Anglia in England who is one of the paper’s two dozen authors, in a telephone interview from Beijing. “But it shows we need to know a more accurate base line for emissions, not only for China but also for the other emissions giants.” |
| The study looked in detail at the coal used as fuel in China, and found that it is generally less rich in carbon and is burned less efficiently than scientists had assumed. That means that each ton of burned coal yields less carbon dioxide than had been thought (as well as less energy, and more ash). | The study looked in detail at the coal used as fuel in China, and found that it is generally less rich in carbon and is burned less efficiently than scientists had assumed. That means that each ton of burned coal yields less carbon dioxide than had been thought (as well as less energy, and more ash). |
| China’s proposed commitments to curtail its emissions of greenhouse gases are crucial to a new international agreement on global warming, which governments hope to reach in Paris late this year. Climate change is also expected to figure in talks between President Obama and his Chinese counterpart, Xi Jinping, when Mr. Xi visits the United States next month. | China’s proposed commitments to curtail its emissions of greenhouse gases are crucial to a new international agreement on global warming, which governments hope to reach in Paris late this year. Climate change is also expected to figure in talks between President Obama and his Chinese counterpart, Xi Jinping, when Mr. Xi visits the United States next month. |
| Mr. Xi promised last year that China’s emissions of carbon dioxide would stop growing by about 2030. Yet uncertainty surrounds just how much of the gas is billowing now from China’s power plants, boilers, motor vehicles and industrial plants. | Mr. Xi promised last year that China’s emissions of carbon dioxide would stop growing by about 2030. Yet uncertainty surrounds just how much of the gas is billowing now from China’s power plants, boilers, motor vehicles and industrial plants. |
| The scientists behind the new study said they analyzed more detailed information about China’s coal quality, combustion performance across industries and total energy consumption than had previously been used. | The scientists behind the new study said they analyzed more detailed information about China’s coal quality, combustion performance across industries and total energy consumption than had previously been used. |
| “We measured thousands of samples of coal from mines across China, and found that the carbon content of the coal being burned in China is actually much lower than what has been assumed in previous estimates of emissions,” Steven J. Davis, a greenhouse gas scientist at the University of California, Irvine, and one of the authors, said in emailed answers to questions. | “We measured thousands of samples of coal from mines across China, and found that the carbon content of the coal being burned in China is actually much lower than what has been assumed in previous estimates of emissions,” Steven J. Davis, a greenhouse gas scientist at the University of California, Irvine, and one of the authors, said in emailed answers to questions. |
| Estimating a country’s carbon dioxide emissions entails some scientific detective work. Researchers start with information about fossil fuel consumption, and then assess how much carbon is contained in those fuels and what fraction of that carbon is actually combusted and ends up in the atmosphere. | Estimating a country’s carbon dioxide emissions entails some scientific detective work. Researchers start with information about fossil fuel consumption, and then assess how much carbon is contained in those fuels and what fraction of that carbon is actually combusted and ends up in the atmosphere. |
| China does not publish official data on annual greenhouse-gas emissions, so “international organizations have to make larger assumptions” than are required for other major countries, said another author of the study, Glen Peters, a senior researcher at the Center for International Climate and Environmental Research-Oslo. | China does not publish official data on annual greenhouse-gas emissions, so “international organizations have to make larger assumptions” than are required for other major countries, said another author of the study, Glen Peters, a senior researcher at the Center for International Climate and Environmental Research-Oslo. |
| Those assumptions often rely on coal carbon content and combustion data collected in the United States and Europe, said Zhu Liu, a postdoctoral research fellow at Harvard University and another of the paper’s authors. But China’s rapidly growing economy mainly uses cheaper, less pure coal from local mines, often burned in less efficient furnaces and boilers than are typical in the West, Dr. Liu said. | Those assumptions often rely on coal carbon content and combustion data collected in the United States and Europe, said Zhu Liu, a postdoctoral research fellow at Harvard University and another of the paper’s authors. But China’s rapidly growing economy mainly uses cheaper, less pure coal from local mines, often burned in less efficient furnaces and boilers than are typical in the West, Dr. Liu said. |
| “Basically, this is the first time we’ve applied real measurement of the coal quality on a national scale in China,” Dr. Liu said. “The quality is not as good as developed countries, so if we use the same amount of coal, we overestimate the carbon content of the coal, and so we overestimate the carbon emissions.” | “Basically, this is the first time we’ve applied real measurement of the coal quality on a national scale in China,” Dr. Liu said. “The quality is not as good as developed countries, so if we use the same amount of coal, we overestimate the carbon content of the coal, and so we overestimate the carbon emissions.” |
| The researchers found that, on average, each lump of coal in China was 40 percent less potent as a source of carbon dioxide emissions than the default figure used for coal by the United Nations’ scientific panel on climate change. | The researchers found that, on average, each lump of coal in China was 40 percent less potent as a source of carbon dioxide emissions than the default figure used for coal by the United Nations’ scientific panel on climate change. |
| This made the researchers’ estimate for China’s total emissions markedly lower than those reached previously by monitoring projects financed by the United States government and the European Commission. The scientists reckon that in 2013, China produced 9.1 billion metric tons of carbon dioxide from fossil fuels and cement production, “which is 14 percent lower than the emissions reported by other prominent inventories,” the study said. | This made the researchers’ estimate for China’s total emissions markedly lower than those reached previously by monitoring projects financed by the United States government and the European Commission. The scientists reckon that in 2013, China produced 9.1 billion metric tons of carbon dioxide from fossil fuels and cement production, “which is 14 percent lower than the emissions reported by other prominent inventories,” the study said. |
| That was despite another finding in the study, that official Chinese figures understated the country’s overall energy consumption by about 10 percent from 2000 to 2012. | That was despite another finding in the study, that official Chinese figures understated the country’s overall energy consumption by about 10 percent from 2000 to 2012. |
| China’s appetite for coal has dulled in the past few years. As economic growth has slowed, new sources of power have come online and the government has shut some smaller, dirtier boilers and furnaces to reduce air pollution. But China still accounts for about half the world’s coal consumption, and experts say that the country’s dependence on coal is unlikely to wane for many years. | China’s appetite for coal has dulled in the past few years. As economic growth has slowed, new sources of power have come online and the government has shut some smaller, dirtier boilers and furnaces to reduce air pollution. But China still accounts for about half the world’s coal consumption, and experts say that the country’s dependence on coal is unlikely to wane for many years. |
| Frank Jotzo, the director of the Center for Climate Economics and Policy at the Australian National University in Canberra, said it was “good news” that Chinese coal was yielding less carbon dioxide, “but it does not change the fundamentals, nor the challenge that China faces in getting away from coal.” Dr. Jotzo was not involved in the new study. | |
| The study looked at Chinese emissions up to 2013, so it does not reflect China’s most recent efforts to curb pollution from fossil fuels. But the authors said those efforts would not significantly change their findings. | The study looked at Chinese emissions up to 2013, so it does not reflect China’s most recent efforts to curb pollution from fossil fuels. But the authors said those efforts would not significantly change their findings. |
| “The carbon content of coal is what it is,” said Dr. Davis of the University of California, Irvine. “The gap between our estimates and previous ones may vary, depending on how much of the burned coal is coming from this mine or that mine in a given year, but as long as most of the coal being burned is from domestic sources, it probably won’t have narrowed much.” | “The carbon content of coal is what it is,” said Dr. Davis of the University of California, Irvine. “The gap between our estimates and previous ones may vary, depending on how much of the burned coal is coming from this mine or that mine in a given year, but as long as most of the coal being burned is from domestic sources, it probably won’t have narrowed much.” |
| He said the study might prompt new questions about how accurately scientists have been estimating other countries’ emissions, and whether the world’s forests have been absorbing as much carbon from the air as they think. | He said the study might prompt new questions about how accurately scientists have been estimating other countries’ emissions, and whether the world’s forests have been absorbing as much carbon from the air as they think. |
| Dr. Liu of Harvard said that accurate data would be needed if a new international treaty on global warming, including national commitments to reduce greenhouse gas emissions, was to succeed. | Dr. Liu of Harvard said that accurate data would be needed if a new international treaty on global warming, including national commitments to reduce greenhouse gas emissions, was to succeed. |
| “If you don’t have the exact numbers, all of the political promises are just some kind of numbers game,” he said. “China has a plan, the U.S. has a plan, different countries have plans. But all of these plans are based on very broad data that has a lot of uncertainty.” | “If you don’t have the exact numbers, all of the political promises are just some kind of numbers game,” he said. “China has a plan, the U.S. has a plan, different countries have plans. But all of these plans are based on very broad data that has a lot of uncertainty.” |