Gigatonne gap in China’s carbon dioxide inventories

China's carbon emissions could be nearly 20 percent higher than previously thought according to a new analysis of official Chinese data, suggesting the pace of global climate change could be even faster than currently predicted.

China is generally reckoned to have overtaken the United States in 2006 to become that world's top greenhouse gas (GHG) emitter and is currently thought to produce about a quarter of mankind's emissions that scientists say is heating up the planet and triggering more extreme weather.

But pinning down an accurate total for China's carbon emissions has long been a challenge because of doubts about the quality of its official energy use data.

"The sad fact is that Chinese energy and emission data as primary input to the models will add extra uncertainty in modeling simulations of predicting future climatic change," say the authors of a study in the journal Nature Climate Change.

The team of scientists from China, Britain and the United States, led by Dabo Guan of the University of Leeds, studied two sets of energy data from China's National Bureau of Statistics. One set presented energy use for the nation, the other for its provinces.

They compiled the carbon dioxide (CO2) emission inventories for China and its 30 provinces for the period 1997-2010 and found a big difference between the two datasets.

"The paper identifies a 1.4-billion tonne emission gap (in 2010) between the two datasets. This implies greater uncertainties than ever in Chinese energy statistics," Guan, a senior lecturer at the School of Earth and Environment at Leeds University, told Reuters in an emailed response to questions.

That is slightly more than the annual emissions of Japan, one of the world's top-five greenhouse gas polluters. Guan noted, however, that China is not the only country with inconsistent energy data.

Scientists say the world is already racing towards a warming of 2 degrees Celsius or more in coming decades because of the rapid growth in emissions from burning fossil fuels and deforestation. Adding another billion tonnes into computer models would accelerate the pace of expected warming.

According to Chinese national statistics, on average, CO2 emissions have been growing 7.5 percent annually from 1997 to 7.69 billion tonnes in 2010, the authors say in the study. In contrast, aggregated emissions of all Chinese provinces have increased 8.5 percent on average to 9.08 billion tonnes in 2010.

The delta of uncertainty is increasing as China’s GHG emissions continue to grow rapidly. In its latest estimate published last month the International Energy Agency said that by increasing its emissions by 9.3 percent -- driven mainly by higher coal use -- China made the largest contribution to a 3.6 percent rise in global emissions during 2011.

Out-of-control coal

The scientists said differences in reported coal consumption and processing at the provincial level were the main contributors to the discrepancy in energy statistics.

The findings also expose the challenges China faces in introducing emissions trading schemes, which need accurate measurement, reporting and verification of energy use and carbon pollution at the local and national level.

Yang Fuqiang, a former Chinese energy official and senior adviser for the Natural Resources Defense Council in Beijing, said provinces routinely underestimate both their carbon emissions and their energy utilization rates.

"I would say the biggest concern about the accuracy and reliability of (China's emissions) data is coal - and that comes from too many small coal mines supplying small enterprises and industrial plants. They have no monitoring systems and, generally speaking, they are also avoiding tax," he said.

With provinces now under pressure to meet targets, they are now likely to underestimate emissions, he added.