China recently overtook America as the world’s largest consumer of energy — also making it the largest emitter of greenhouse gas emissions. Led by China, countries pumped record levels of CO2 into the atmosphere in 2011, setting the world on a path to 11 degree Fahrenheit warming by the end of the century.

If that prospect isn’t worrisome enough, consider this: China’s emissions could be as much as 20 percent higher than previously reported.

According to an international team of researchers, there’s a massive gap between China’s national and provincial emissions figures. And as China’s emissions skyrocket, that gap is growing. In 2010, the difference between the two data sets is 1.4 Gt of CO2 — or roughly the yearly emissions of Japan.

The findings were published in the journal Nature Climate Change:

China’s emission discrepancy in 2010 is equivalent to about 5% of the global total (in 2008) and higher than the CO2 emissions of the world’s fourth largest emitter—Japan, or the combined emissions of all African countries. The emission gap is mainly due to the inconsistencies of coal consumption between national and provincial statistics. For example, emissions caused by coal consumption contribute 71% of the emission discrepancy in 2010, whereas emissions from petroleum, natural gas and other fuels (including coke oven gas, other gas, other coking products, LPG, refinery gas and other petroleum products) account for 12%, 2% and 14%, respectively. The data situation is better when accounting cement processing emissions, which show a much smaller difference between provincial and national statistics.

This difference in reported data has huge consequences: It makes the job of climate scientists modeling emissions and warming scenarios more difficult; it makes international agreements on emissions cuts more murky; and it makes it harder for China to properly monitor regional cap and trade markets that provinces are beginning to roll out.

Oh, and it means that our current emissions path, which experts already say will have “devastating consequences for the planet,” may be conservative.

Discrepancies in reported pollution data are a common problem in China. Officials in the country have been repeatedly called out for using shoddy methods for measuring air pollution, calling “hazardous, emergency-condition” levels of air pollution “minor.” China’s pollution reporting has been so poor, the government has called on other countries not to release its national air quality data.

The explosion in Chinese carbon emissions is mostly due to a stunning rise in coal consumption. More than 70 percent of the “gap” comes from burning coal. And a growing chunk of that coal is coming from the United States, where producers are looking for new international markets to offset the decline in domestic consumption.