Study Highlights Need to Adjust Climate Models

Michael Kahn, PlanetArk 26 Jun 08;

LONDON - Sea spray and microscopic plants from the tropical Atlantic are destroying greenhouse gases in the lower atmosphere at a faster pace than scientists had thought, British researchers said on Wednesday.

The findings published in the journal Nature mean current climate models may need adjusting and they underscore the difficulties in trying to predict future temperature changes, the researchers said.

"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)

Tropical oceans expose riddle over global-warming equation
Marlowe Hood, Yahoo News 26 Jun 08;

A probe into levels of an important greenhouse gas above the tropical Atlantic has challenged assumptions about key sources of global warming, scientists said on Wednesday.

Researchers found that natural chemicals in the atmosphere west of equatorial Africa destroyed 50 percent more ozone in that region than expected.

This process also reduced concentrations of methane, another powerful greenhouse gas.

It may well apply in oceans around the world and if so, it would pose major questions about how Earth's inventory of global warming gases is calculated, they said.

Ozone, a naturally-occurring molecule composed of three oxygen atoms, can be beneficial or harmful to human life, depending on where it is.

In the stratosphere, 10 to 50 kilometres (17 to 31 miles) above Earth's surface, ozone protects living things by filtering out the Sun's damaging ultraviolet light.

But in the troposphere, or lower atmosphere, ozone is a noxious pollutant and the most important greenhouse gas after carbon dioxide (CO2), methane and water vapour, which thus makes it a driver of global warming.

Scientists led by John Plane at the University of Leeds, northern England, analysed a year of ozone and methane measurements taken at the Cape Verde Atmospheric Observatory on Sao Vicente, an island some 500 kilometres (380 miles) west of Senegal.

Ozone, a short-lived molecule with a lifetime ranging from a few days to a week, was disappearing at a rate far above what theoretical calculations would have forecast.

Using new instruments developed for their study, the researchers gave the credit to two atmospheric chemicals produced by sea spray and emissions from microscopic sea organisms called phytoplankton: bromine and iodine oxide.

These chemicals attack ozone and break it down, said the study, published in the British journal Nature.

They also boost the atmospheric levels of another compound called the hydroxyl radical, which in turn destroys methane.

This unexpected discovery implies that the mathematical model for calculating the various sources of global warming could be flawed, although global warming itself is not being contested, one of its authors said.

"Global models get levels of ozone in the troposphere about right. So if destruction rates are much higher than thought that means it must be coming from somewhere else," University of York scientist Lucy Carpenter told AFP.

Whether the findings are good news or bad is a matter of interpretation, Carpenter said.

"These gases are being destroyed more rapidly than we supposed," she said.

"That is good because if humans produce less methane, then it might settle at a lower level."

At the same time, however, that would expose a worrying gap in knowledge -- a hole in the balance sheet of greenhouse gases that needed to be explained.

Further work is needed to see whether the phenomenon observed in the tropical Atlantic applies elsewhere, and also to find whether bromine and iodine oxide levels are on the increase.

If they are -- and it would take five years to find out -- the world's oceans could play a bigger role in reducing at least two of the greenhouse gases driving climate change, she said.