GREENHOUSE gas emissions in the 1990s could have been underestimated by billions of tonnes, throwing doubt on some of the maths behind the Kyoto Protocol, research by Australian and international scientists suggests.
The research team measured real-world changes in the amount of CO2 building up in the atmosphere against the amount of gases that each country said it emitted. And, like a jigsaw puzzle with one or two missing pieces, the picture did not quite match.
''The simplest explanation is there has been an underestimate in the accounting of about 7 per cent through that early period in the 1990s,'' said the lead researcher, Roger Francey, an honorary fellow at the CSIRO.
''The increase in CO2 in the atmosphere doesn't reflect the reported emissions. This may be because the methodology for getting national emissions was far less developed than today, and only really developed for a few countries, so they were relying much more on estimates.''
If confirmed, the findings would carry some potentially good news about the rate of climate change: if emissions were higher in the 1990s, then they have not been increasing at quite such a steep rate to reach today's level. It would mean emissions have been rising more steadily for the past three decades, at the middle range of predictions by Intergovernmental Panel on Climate Change, rather than surging up since 2000.
The group's findings are contained in a paper published on Monday in the journal Nature Climate Change.
Although an error of 7 per cent in estimated emissions is within the stated level of uncertainty, it still means that emissions equivalent to about four times the size of Australia's annual greenhouse output had somehow been ''lost''. The accounting method is made even more complicated by the performance of ''carbon sinks'' which absorb large but varying amounts of carbon out of the atmosphere.
''When they were adding up all the emissions from around the world back then … it's understandable that there might have been significant errors,'' said the head of the CSIRO's Changing Atmosphere group, Paul Fraser. ''Exactly how that may have happened, it's hard to know … What it shows is that the IPCC estimates of more recent times have got it about right.''