The rapid growth of China’s export-driven economy earlier this decade fueled a dramatic increase in carbon dioxide emissions that overwhelmed the country’s substantial improvement in energy efficiency, a new analysis reveals.

China’s recent economic growth has made the country the world’s third-largest exporter and its fourth-largest economy. It has also made the Asian dynamo, in one sense, the world’s largest polluter: In 2006, China passed the United States to become the world’s largest emitter of carbon dioxide, the most prevalent anthropogenic greenhouse gas.

Between 2002 and 2007, China’s energy consumption nearly doubled, says Glen Peters, a climate scientist at the Center for International Climate and Environmental Research–Oslo. Now Peters and his colleagues have conducted the first detailed analysis indicating which sectors of the Chinese economy most substantially contributed to the dramatic surge in CO₂ emissions. The researchers focused on the period between 2002 and 2005, the most recent year for which detailed data are available.

Between 2002 and 2005, China’s production-related CO₂ emissions rose by about 46 percent, from 3.4 billion metric tons to about 4.98 billion metric tons, the researchers report in the Feb. 28 Geophysical Research Letters. Population growth and changes in consumer consumption patterns — the mix of products that people living in the country buy — are responsible for only about 3 of those percentage points, Peters notes. Gains in energy efficiency across the spectrum, from upgraded technology in coal-fired power plants to more-efficient home appliances, would actually have decreased the country’s emissions by 21 percent, if all other factors had remained unchanged, the researchers contend. But there’s the rub: During this period, the explosive growth of manufacturing and a widespread construction boom sent CO₂ emissions through the roof.

Until 2002, manufacturing accounted for about 38 percent of China’s gross domestic product, says Peters. By 2005, that fraction had increased to 46 percent, and much of that jump was because of the energy-intensive fabrication of products such as electronics and machinery. The number of TV sets manufactured for export more than quadrupled from 2002 to 2005. At least half of the increase in CO₂ emissions between 2002 and 2005 stemmed from the production of goods for export, with most of those items destined for the developed world. In essence, says Peters, developed nations have outsourced many of their carbon dioxide emissions to China.

About 15 percent of the increased emissions from 2002 to 2005 resulted from construction, particularly from urbanization and the building of infrastructure — both of which consume large amounts of cement, which emits copious amounts of carbon dioxide as it hardens. In that four-year interval, the number of kilometers of highways in the country increased about 90 percent. During this period, “China was one big construction site,” Peters notes.

Better highways and fatter wallets led to a rise in the number of cars sold in the country. Vehicle emissions are a small part of Chinese emissions now, but are poised to skyrocket: In 2005 there were only 3.5 autos for every 100 households in China, compared with less than 1 per 100 households in 2002.

The sizeable growth of China’s greenhouse gas emissions compared with U.S. emissions “is a trend that is not changing,” says Tom Boden, a climate scientist at the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory in Tennessee. “They’re not just passing us, they’re sailing by,” he notes.

The dramatic boost in China’s export-related economy suggests that worldwide efforts to restrict carbon dioxide emissions should perhaps track emissions based on where a product is consumed, not where it’s manufactured, says Gregg Marland, an environmental scientist also at the lab in Oak Ridge. All of the emissions ultimately end up in the atmosphere, and “the climate doesn’t care where they came from,” he notes.

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