A study into car emissions in the Chinese city of Chengdu - carried out using data from companies including Uber - suggests that current lab testing could be off by up to 6,500 metric tonnes per day. Graham Machay reports. A damning indictment of carbon emissions testing in China - brought to you, in part, by Uber. A report released on Tuesday suggesting that C)2 pollution in the city of Chengdu could be underestimated by more than half. A local think thank carried out the study using data from Uber and other taxi companies. It found that standard emissions estimated were off by about 6 and-a-half metric tonnes per day - that's nearly 60 percent. The team that led the research says i's better to use data from cab firms because it rules out cheating by local governments and carmakers. Researchers say if this model takes off, it could one day be used across China. And that cities, even companies could eventually be ranked by their carboon footprint.