The uncertainty about Chinese emissions is, it turns out, as large total emissions of India:

Source: Trends in global CO2 emissions: 2013 Report

The chart above shows fossil-fuel combustion and cement production added together, so it's possible it excludes some source sectors, such as fugitive emissions from fuels, feedstock and other non-energy uses of fossil fuels, and waste incineration.

Given the large and creasing size of the shaded uncertainty area, it seems like investment into data collection is needed. It's a cliche, yes, but good policy does require good data.