Concentrations of carbon dioxide (CO2) in the atmosphere were recorded to have surpassed the symbolic 400 parts per million (ppm) threshold at several stations of the World Meteorological Organization(WMO)'s Global Atmosphere Watch (GAW) network, the UN agency said Tuesday.

Clare Nullis, spokeswoman of WMO, told a press conference that along with several other GAW stations, the station of Mauna Loa in Hawaii which is widely regarded as a benchmark site in the GAW for its longest history in the world of continuously carrying out atmospheric measurement since 1958, reported CO2 concentrations exceeding the 400 ppm threshold during the seasonal maximum.

WMO said that according to statistics from the United States, the daily mean concentration of CO2 in the atmosphere of Mauna Loa recorded a reading of 400.03 ppm on May 9.

"It is a wakeup call that the levels of carbon dioxide, which is the most important greenhouse gas, in the atmosphere are constantly rising," said Nullis.

According to the meteorological organization, the threshold was first crossed at stations located in the Arctic area, with a monthly average value exceeding 400 ppm registered at Barrow, Alaska, the United States for the first time in April 2012, as well as at Alert, in Canada; from the beginning of 2013, another GAW station in Ny-Alesund, Norway, recorded the measured CO2 values exceeding 400 ppm.

The organization pointed out that the concentration level of CO2 exceeding the threshold tended to be registered in stations nearer to the Equator, with Izana, (Canary Islands, Spain), reporting daily mean values exceeding 400 ppm at the end of April 2013, which was followed by Mauna Loa.

"What is important to remember is that carbon dioxide lasts in the atmosphere for hundreds if not thousands of years, so what is going up there now will stay in our atmosphere for very long time. It will continue to trap heat and (this) means that our palnet will warm," warned Nullis.

WMO alerted that the global annual average CO2 concentration is set to cross the 400 ppm threshold in 2015 or 2016, if the amount of CO2 in the atmosphere keeps rising at the current rate, which has risen on average by 2 parts per million per year for the past decade. Endi

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