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Over The Horizon

Gas Cloud Over New Zealand

The biggest build-up of atmospheric methane gas since 1991-92 is building up over New Zealand, says National Institute of Water and Atmospheric Research scientist Dr David Lowe.

The build-up is a new development, discovered as part of NIWA's on-going research into greenhouse gases and climate change. The pollution is being measured by instruments at Baring Head, near the entrance to Wellington harbour.

Lowe says the build-up could have been caused by recent changes in methane sources in the Northern Hemisphere, as well as tropical forest burning in South-East Asia or in the Amazon areas of Brazil. He says the effects of the build-up are not yet known.

"By adding large amounts of industrial and agricultural waste gases to the atmosphere, we are dramatically altering its chemical properties," he says. "This will lead to unexpected consequences. An obvious example of this is the ozone hole that was not predicted by the best scientists in the field in the 1970s.

"So the message for New Zealand is, I'm afraid: Watch this space'."

He says NIWA is measuring greenhouse gases from the Northern Hemisphere and from Asia, partly by fitting instruments to Blue Star Line container ships that travel between New Zealand and North America.

"The ships go through what is known as the inter-tropical convergence zone, where Northern and Southern Hemisphere air masses come together. There is a lot of dirty air in this region, much of it originating from large-scale seasonal tropical forest and savannah burning, as well as industrial sources in the Northern Hemisphere."

The inter-tropical convergence zone moves seasonally in the Pacific and acts as a buffer zone between the air movements of the hemispheres.

"We are using our measurements from the container ships to help figure out how air breaks through this zone and moves down to the New Zealand region."