"One of the key things we need to do in the future is reduce uncertainty around the natural processes that destroy greenhouse gases," said Alastair Lewis of Britain's National Centre for Atmospheric Science, who helped lead the study.

"This is one of the first times we have been able to go and see how those models were doing at predicting the rate of destruction of some greenhouse gases."

Year-round measurements from an observatory on the Cape Verde island of Sao Vicente allowed the team to measure how fast the chemicals bromine and iodine oxide -- produced from sea spray and phytoplankton -- attack and break down ozone.

They found that the chemicals were gobbling up 50 percent more ozone in the part of the lower atmosphere -- about 1 kilometre above the Earth's surface -- than current climate models suggest. Ozone in the lower atmosphere acts as a greenhouse gas, and its destruction sets off a chain of chemical reactions that leads to the removal of methane, the third most abundant greenhouse gas. In the upper atmosphere it helps shield the planet from harmful solar rays.

The study was also the first to take such readings from the ozone above the open ocean. Researchers say they believe the findings are likely typical of other similar tropical waters.

But the findings also has their worrying aspect, the researchers said.

While the results indicate the atmosphere will clean itself faster in response to decreases in human-generated emissions, they also mean climate models slightly underestimate these greenhouse gases, said Lucy Carpenter, who worked on the study.

"At the moment climate models get the amount of ozone right but they haven't got the destruction rates right," said Carpenter, an atmospheric chemist at York University in Britain.

"It also means the models haven't got the balance between production and destruction; because if methane is being destroyed more rapidly it means there must be more emmissions than we had thought." (Reporting by Michael Kahn; Editing by Maggie Fox and Ralph Boulton)