Tried to submit this as part of a reply...would not allow.
Not a big fan of the new comment format.

The Intergovernmental Panel on Climate Change has published a five-volume set of guidelines that all the countries now use, as part of the UN Framework Convention on climate change, for estimating emissions on all greenhouse gases and it does produce uniformity across countries.  The error margin depends on the country and on the greenhouse gas.  I think the interest is partly in carbon dioxide emitted from energy systems, and in that case, it really depends on how much a country invests in collecting energy statistics.  For countries like those in the EU or the US or Japan, my guess is that the error margin is something in the order of plus or minus 5%.  For those discharging smaller quantities of CO2, the error bars, I think can be as high as 20 to 25% and there are some very large countries – in China, we’ve actually published the estimate that they are maybe as large as 15 or 20