WELLINGTON, June 7 (Xinhua) -- Researchers in New Zealand said Tuesday that the planet has just reached a significant milestone in the build-up of atmospheric carbon dioxide - a major contributor to climate change.
The government's National Institute of Water and Atmospheric Research (NIWA) said a clean air monitoring station at Baring Head, at the bottom of the North Island, had recorded carbon dioxide readings passing 400 parts per million (PPM) level for the first time.
The level was last reached more than 3 million years ago.
The Baring Head station, which has been operating since 1972, boasts the longest running continuous carbon dioxide record in the Southern Hemisphere and is one of a network of similar stations around the world.
Most emissions occurred in the Northern Hemisphere, so the 400 ppm threshold had already been passed at stations to the north of New Zealand, said a statement from NIWA.
However, enough gas had now mixed through the atmosphere and reached the high latitude Southern Hemisphere stations to push the level over 400 ppm.
Baring Head was particularly significant because the air arriving there during steady interval conditions originated far to the south of the site, away from human activities.
NIWA atmospheric scientist Dr Sara Mikaloff-Fletcher said she and her colleagues have known the level would be reached for some time.
It was "a bit like turning 40 and realizing you haven't started saving for your retirement," she said in the statement.
"It was already a problem when you turned 38 and 39, but this is a natural time to stop and take stock. It is a useful point to recognize that because we have left things so long, there is very limited opportunity to get back on track and stop drastic climate change."
Carbon dioxide levels had been steadily increasing for decades, although there was a "tiny" flattening out during the Global Financial Crisis.
"This is a path we have been on for a very long time. The 400 ppm threshold represents an opportunity for people to recognize this landmark and understand that there is only a small amount of time to accomplish change."
Reducing the levels to below 400 ppm would likely take many years of emissions reduction.
