One of the major greenhouse global warming gases is methane. Scientists have discovered that there is not nearly as much methane in the atmosphere as their computer models predicted there should be.
Scientists say that there has been a mysterious decline in the growth of methane in the atmosphere in the last decades of the 20th Century.
Researchers writing in the journal Nature have come up with two widely differing theories as to the cause.
One suggests the decline was caused by greater commercial use of natural gas, the other that increased use in Asia of artificial fertiliser was responsible.
Both studies agree that human activities are the key element.
And there are suggestions that methane levels are now on the rise again.
Methane is regarded as one of the most potent greenhouse gases, trapping over 20 times more atmospheric heat than carbon dioxide.
Since the start of the industrial revolution, levels of methane in the atmosphere have more than doubled from a wide variety of sources, including energy production, the burning of forests, and increased numbers of cattle and sheep.
But between 1980 and the turn of the millennium, the growth rate reduced substantially, leaving scientists puzzled as to the cause.
Now, two teams of researchers have arrived at two very different conclusions for the decline. The first study was led by Dr Murat Aydin from the University of California, Irvine.
“We went after ethane – it’s another hydrocarbon similar to methane, it has common sources, but is easier to trace. We determined what ethane did during the second half of the 20th century using ancient air that we collected at polar ice sheets.
“We think the trend we see in methane is best explained by dramatic changes in emissions linked to fossil fuel production and use which seem to have declined in the 1980s and 1990s.
The big question, then, is what this does to the global warming scare.