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Carbon dioxide (CO2) levels reached 400 parts per million (ppm) throughout the northern hemisphere in April for the first time, according to the World Meteorological Organization (WMO).
All the northern hemisphere monitoring stations forming the WMO's Global Atmosphere Watch network reported record atmospheric CO2 concentrations during the seasonal maximum. This occurs early in the northern hemisphere spring before vegetation growth absorbs CO2.
The level 400ppm means that within every cubic meter of dry air, a volume of 400 cubic centimeters – just under a pint – is made up of CO₂. The precise figure 400 is in itself is just a number and has no particular physical significance but the level of 400ppm is seen as a significant milestone by many climate scientists and others. “This should serve as yet another wakeup 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,” WMO Secretary-General Michel Jarraud was quoted as saying in a WMO news release (see below). “Time is running out.”
The Arctic monitoring site in Barrow in Alaska managed by the National Oceanic and Atmospheric Administration (NOAA) of the US first reported 400ppm levels in the Spring of 2012. Since then, levels measured on NOAA's Mauna Loa mountain observatory in Hawaii topped 400ppm for the first time on 9 May 2013.
In general, levels of CO2 are higher in the northern hemisphere that in the southern hemisphere. And CO2 concentrations on the southern hemisphere tend to lag behind. NOAA predicts that the global average will reach 400ppm in 2016. Eventually, some time around 2020, the 400ppm level will be reached in the Antarctic; and then the whole world will record levels at or above 400ppm.
Here is the text of the press release issued by the WMO.
Geneva, 26 May 2014 (WMO) - For the first time, monthly concentrations of carbon dioxide (CO2) in the atmosphere topped 400 parts per million (ppm) in April throughout the northern hemisphere. This threshold is of symbolic and scientific significance and reinforces evidence that the burning of fossil fuels and other human activities are responsible for the continuing increase in heat-trapping greenhouse gases warming our planet.
All the northern hemisphere monitoring stations forming the World Meteorological Organization (WMO) Global Atmosphere Watch network reported record atmospheric CO2 concentrations during the seasonal maximum. This occurs early in the northern hemisphere spring before vegetation growth absorbs CO2.
Whilst the spring maximum values in the northern hemisphere have already crossed the 400 ppm level, the global annual average CO2 concentration is set to cross this threshold in 2015 or 2016.
“This should serve as yet another wakeup 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,” said WMO Secretary-General Michel Jarraud. “Time is running out.”
CO2 remains in the atmosphere for hundreds of years. Its lifespan in the oceans is even longer. It is the single most important greenhouse gas emitted by human activities. It was responsible for 85% of the increase in radiative forcing – the warming effect on our climate - over the decade 2002-2012.
Between 1990 and 2013 there was a 34% increase in radiative forcing because of greenhouse gases, according to the latest figures from the U.S. National Oceanic and Atmospheric Administration (NOAA).
According to WMO’s Greenhouse Gas Bulletin, the amount of CO2 in the atmosphere reached 393.1 parts per million in 2012, or 141% of the pre-industrial level of 278 parts per million. The amount of CO2 in the atmosphere has increased on average by 2 parts per million per year for the past 10 years.
Since 2012, all monitoring stations in the Arctic have recorded average monthly CO2 concentrations in spring above 400 ppm, according to data received from Global Atmosphere Watch stations in Canada, the United States of America, Norway and Finland.
This trend has now spread to observing stations at lower latitudes. WMO’s global observing stations in Cape Verde, Germany, Ireland, Japan, Spain (Tenerife) and Switzerland all reported monthly mean concentrations above 400 ppm in both March and April.
In April, the monthly mean concentration of carbon dioxide in the atmosphere passed 401.3 at Mauna Loa, Hawaii, according to NOAA. In 2013 this threshold was only passed on a couple of days. Mauna Loa is the oldest continuous CO2 atmospheric measurement station in the world (since 1958) and so is widely regarded as a benchmark site in the Global Atmosphere Watch.
The northern hemisphere has more anthropogenic sources of CO2 than the southern hemisphere. The biosphere also controls the seasonal cycle. The seasonal minimum of CO2 is in summer, when substantial uptake by plants takes place. The winter-spring peak is due to the lack of biospheric uptake, and increased sources related to decomposition of organic material, as well as anthropogenic emissions. The most pronounced seasonal cycle is therefore in the far north.
The WMO Global Atmosphere Watch coordinates observations of CO2 and other heat-trapping gases like methane and nitrous oxide in the atmosphere to ensure that measurements around the world are standardized and can be compared to each other. The network spans more than 50 countries including stations high in the Alps, Andes and Himalayas, as well as in the Arctic, Antarctic and in the far South Pacific. All stations are situated in unpolluted locations, although some are more influenced by the biosphere and anthropogenic sources (linked to human activities) than others.
The monthly mean concentrations are calculated on the basis of continuous measurements. There are about 130 stations that measure CO2 worldwide.
A summary of current climate change findings and figures is available here
WMO news release here.
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