Air monitors in Switzerland have detected large quantities of one gas coming from a location in Italy.
However, the Italian submission to the UN records just a tiny amount of the substance being emitted.
Levels of some emissions from India and China are so uncertain that experts say their records are plus or minus 100%.
These flaws posed a bigger threat to the Paris climate agreement than US President Donald Trump's intention to withdraw, researchers told BBC Radio 4's Counting Carbon programme.
Bottom-up records