Among the key provisions of the Paris climate deal, signed by 195 countries in December 2015, is the requirement that every country, rich or poor, has to submit an inventory of its greenhouse-gas emissions every two years. Under UN rules, most countries produce "bottom-up" records, based on how many car journeys are made or how much energy is used for heating homes and offices.
But air-sampling programmes that record actual levels of gases, such as those run by the UK and Switzerland, reveal omissions.
In 2011, Swiss scientists first published their data on levels of a gas called HFC-23 coming from a location in northern Italy. "Our estimate for this location in Italy is about 60-80 tonnes of this substance being emitted every year, then we can compare this with the Italian emission inventory, and that is quite interesting because the official inventory says below 10 tonnes or in the region of two to three tonnes," said Dr Stefan Reimann, from the Swiss Federal Laboratories for Materials Science and Technology.
Carbon tetrachloride, once popular as a refrigerant and a solvent but very damaging to the ozone layer, has been banned in Europe since 2002. But Dr Reimann explained, "We still see 10,000-20,000 tonnes coming out of China every year. That is something that shouldn't be there. There is actually no Chinese inventory for these gases, as they are banned and industry shouldn't be releasing them anymore."
China's approach to reporting its overall output of green-house global warming gases to the UN is also subject to constant and significant revisions. Its last submission ran to about 30 pages - the UK's, by contrast, runs to several hundred.
Back in 2007, China simply refused to accept, in official documents, that it had become the largest emitter of CO2.
"I was working in China in 2007," said Dr Angel Hsu, from Yale University. "I would include a citation and statistics that made this claim of China's position as the number one emitter - these were just stricken out, and I was told the Chinese government doesn't yet recognise this particular statistic so we are not going to include it."
A report in 2015 suggested one error in China's statistics amounted to 10% of global emissions in 2013.
"What we're worried about is what the planet experiences, never mind what the statistics are," said Prof Euan Nisbet, from Royal Holloway, University of London. "In the air, we see methane going up. The warming impact from that methane is enough to derail Paris."
Prof Glen Peters, from the Centre for International Climate Research, in Oslo, said: "The core part of Paris is the global stock-takes which are going to happen every five years, and after the stock-takes countries are meant to raise their ambition, but if you can't track progress sufficiently, which is the whole point of these stock-takes, you basically can't do anything. So, without good data as a basis, Paris essentially collapses. It just becomes a talkfest without much progress."
Meanwhile, Staff at the US Department of Agriculture (USDA) have been told to avoid using the term climate change in their work, with the officials instructed to reference “weather extremes” instead. Rather “climate change adaption”, staff are asked to use “resilience to weather extremes”. The term “reduce greenhouse gases” is blacklisted in favor of “build soil organic matter, increase nutrient use efficiency”. While, “sequester carbon” is ruled out and replaced by “build soil organic matter”.