Unless we do something drastic soon, we're in for a big redrawing of coastal boundaries, said Victoria University's Dr James Renwick.

New Zealand will pass an important climate change milestone within weeks, a leading researcher says.



Readings of atmospheric carbon dioxide (CO²) will hit 400 parts per million at the Baring Head Clean Air Monitoring Station on Wellington's south coast within weeks, Dr James Renwick predicted. He is a professor of physical geography at Victoria University and was a lead author on the fifth assessment report of the Intergovernmental Panel of Climate Change (IPCC) .



The last time CO² levels were at 400ppm, about 3 million years ago, earth temperatures were 2-3 degrees Celsius higher and sea levels were about 20 metres higher, Renwick told an AntarcticaNZ conference on the weekend.



"Unless we do something drastic soon, we're in for a big redrawing of coastal boundaries," Renwick said.

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In simple terms, the climate can be changed by either altering the amount of sunlight arriving or by changing the amount of greenhouse gases such as CO² in the atmosphere, he said. "That's what we've been doing."

Aaron Wood .

While there is variation in the atmosphere due to events such as El Nino, "the background trend is very obviously upward," Renwick said.

The best known atmospheric monitoring station, at Mauna Loa in Hawaii, passed 400ppm in November. The Australian monitoring station at Cape Grim on Tasmania passed 400ppm in mid May.

"We're leaving a big fingerprint on the earth ... it's a kick in the guts," Renwick said.

The fifth IPCC report was a "great thing but it was out of date as soon as it' was published," Renwick said. "Every week a new (academic) paper comes out."

"We're starting to get a much more detailed picture of what's happening globally," Renwick said.

Skeptics claim climate records are too short – from the early 1970s in the case of Baring Head – given the millions of years of climate history. Renwick said the geological record, ice cores and the like provided enough data to be confident that predictions would turn out to be accurate.

Last year 196 nations signed a climate change agreement in Paris with the intention of capping global temperature increases at 2C by 2030. That was a "political" target, not a scientific one, Renwick said.

This week's budget phased out an emissions trading scheme subsidy that was used by businesses to offset their greenhouse gas emissions.