Greenhouse gas level highest in 2 million yearsWASHINGTON: Worldwide levels of the greenhouse gas that plays the biggest role in global warming
have reached their highest level in almost 2 million years, an amount
never before encountered by humans, US scientists said on Friday.
Carbon dioxide was measured at 400 parts per million Thursday at the
oldest monitoring station in Hawaii, which sets the global benchmark.
The number 400 has been anticipated by climate scientists and
environmental activists for years as a notable indicator, in part
because it's a round number.
"What we see today is 100 percent due to human activity," said Pieter Tans, a senior scientist with the National
Oceanic and Atmospheric Administration. The burning of fossil fuels,
such as coal for electricity and oil for gasoline, has caused the
overwhelming bulk of the man-made increase in carbon in the air,
At the end of the Ice Age, it took 7,000 years
for carbon dioxide levels to rise by 80 parts per million, Tans said.
Because of the burning of fossil fuels, carbon dioxide levels have gone
up by the same amount in just 55 years.
The speed of the change is the big worry, said Pennsylvania State University climate scientist Michael Mann. If carbon dioxide levels go up 100 parts per million over thousands or millions of years, plants and animals can adapt. But that can't be done at the speed it is now happening.
The last time the worldwide carbon level was probably this high was
about 2 million years ago, Tans said. That was during the Pleistocene
"It was much warmer than it is today," Tans said. "There
were forests in Greenland. Sea level was higher, between 10 and 20
meters (33 to 66 feet)."
Other scientists say it may have been 10 million years since Earth last encountered this level of carbon dioxide.
When measurements were first taken in 1958, carbon dioxide was measured
at 315 parts per million. Levels are now growing about 2 parts per
million per year. That's 100 times faster than at the end of the Ice
Before the Industrial Revolution, carbon dioxide levels were around 280 ppm, and they were closer to 200 during the Ice Age.
There are natural ups and downs of the greenhouse gas, which comes from
volcanoes and decomposing plants and animals. But that's not what has
driven current levels so high, Tans said. He said the amount should be
even higher, but the world's oceans are absorbing quite a bit, keeping
it out of the air.
Carbon dioxide traps heat just like in a
greenhouse and most of it stays in the air for about a century. Some
lasts for thousands of years, scientists say.
Last year, regional monitors briefly hit 400 ppm in the Arctic, but those monitoring stations aren't seen as a world mark like the one at Mauna Loa, Hawaii.
Generally carbon levels peak in May then fall slightly, so the yearly
average is usually a few parts per million lower than May levels.