GENEVA May 26 Carbon dioxide levels throughout
the northern hemisphere hit 400 parts per million (ppm) for the
first time in human history in April, an ominous threshold for
climate change, the World Meteorological Organization said on
The 400 ppm level in the atmosphere, up 40 percent since
wide use of fossil fuels began with the Industrial Revolution,
is rapidly spreading southwards. First recorded in 2012 in the
Arctic, it has since become the norm for the Arctic spring.
The WMO expects the global annual average carbon dioxide
concentration to be above 400 ppm in 2015 or 2016. Rising
concentrations of the heat-trapping gas raise risks of more
heatwaves, droughts and rising sea levels.
"Time is running out," WMO Secretary-General Michel Jarraud
said in a statement.
"This should serve as yet another wake-up call about the
constantly rising levels of greenhouse gases which are driving
climate change. If we are to preserve our planet for future
generations, we need urgent action to curb new emissions of
these heat-trapping gases."
Almost 200 governments have agreed to work out a deal by the
end of 2015 to slow climate change as part of efforts to limit
the average temperature increase to two degrees Celsius (3.6
degrees Fahrenheit) above pre-industrial times.
Temperatures have already risen about 0.8C (1.4F).
In April, the U.N.'s panel of climate experts said that
greenhouse gas concentrations, led by carbon dioxide, would have
to be kept below 450 ppm to give a good chance of achieving the
The level of carbon dioxide in the atmosphere is seasonal,
since plants absorb more in the summer months, causing a peak in
the spring. The northern hemisphere, with more human-related
sources of the gas, has a more pronounced seasonal cycle.
Carbon dioxide remains in the atmosphere for hundreds of
years. It is emitted by fossil-fueled vehicles and coal-fired
factories and power plants as well as by natural activities such
During the last 800,000 years, the level of atmospheric
carbon dioxide fluctuated between 180 ppm and 280 ppm, and has
probably not been above 400 ppm for millions of years,
With the widespread burning of coal and oil during the
Industrial Revolution, the concentration of carbon dioxide rose
to about 290 ppm by the end of the 19th century.
That accelerated last century, with levels between 370 and
380 ppm by the year 2000. An animated graph that shows the
history of atmospheric carbon dioxide is online here.
(Reporting by Tom Miles, editing by Alister Doyle)