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| The Keeling Curve shows that atmospheric carbon dioxide levels are increasing |
The proportion of carbon dioxide in the atmosphere broke 400 parts per million Thursday (May 9), according to one of the best climate records available.
The Keeling Curve,
a daily record of atmospheric carbon dioxide, has been running
continuously since March 1958, when a carbon dioxide monitor was
installed at Mauna Loa in Hawaii. On the first day, the observatory
measured a carbon dioxide concentration of 313 parts per million (ppm).
The number means there were 313 molecules of carbon dioxide in the air
per every million air molecules.
Now, the Keeling Curve has reached 400 ppm for the first time in human
history, with a new measure of 400.03 ppm. The data are preliminary,
pending quality control checks, according to the National Oceaninc and
Atmospheric Administration (NOAA).
The rollover from 399 won't make an appreciable difference in climate
by itself, but the continuing rise in greenhouse gas concentration is
already doing so, climate scientists say.
A concentration of 400 ppm is a new high-water mark, of course, and
more than anything else, has symbolic significance,
Upward creep
Each year, the Keeling Curve shows an increase in carbon dioxide in the
atmosphere which peaks in May. The number then drops, reaching a
minimum in October. This maximum-minimum pattern, repeated seasonally,
reveals how trees withdraw carbon dioxide from the air in summer to grow
and then release it through dead, decaying leaves and wood in the
winter.
But humans release carbon dioxide into the air, too, by burning fossil fuels.
This activity has caused the Keeling Curve to creep ever upward since
1958: The lows get a little higher each year, as do the highs. It is a reminder of just how uncontrolled this dangerous experiment
we're playing with the planet really is..
What 400 ppm means
In the 1,000 years before the Industrial Revolution of the 18th
century, atmospheric carbon dioxide held steady at around 270 to 280
parts per million.
Scientists believe that the most recent period with a 400 ppm level of
carbon dioxide in the atmosphere was the Pliocene, between five million
and three million years ago, according to the Scripps Institution of
Oceanography, which keeps track of the Keeling Curve.
It was a different world. Global average temperatures were between 5.4
and 7.2 degrees Fahrenheit (3 to 4 degrees Celsius) higher than today,
and sea level was as much as 131 feet (40 meters) higher in some places.
Even the least-affected regions saw sea-level rises 16 feet (5 meters) higher than today's.
A major difference, though, is the speed at which carbon dioxide is
rising today. Typically, the Keeling Curve shows increases of 2 to 2.5
ppm a year, Mann said. In the 1950s and 1960s, carbon dioxide increased
by less than 1 ppm each year, according to Scripps Institution of
Oceanography.
We're on course for more than 450 ppm in a matter of decades if we don't get our fossil fuel emissions under control quite soon.
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