In a statement, the U.S. National Oceanic and Atmospheric Administration announced that in May the Earth experienced the highest concentration of carbon dioxide in the

atmosphere, at 50 percent of pre-industrial levels and had never been recorded in nearly four million years. While citing the causes of climate warming resulting from activities such as transport, cement production, deforestation and fossil fuel electricity production, the Board recalled that the phenomenon had begun to lead to "serious consequences", most notably increasing heat waves, droughts, fires and floods.

It is reported that the month of May is usually the month in which each year the highest levels of carbon dioxide are recorded.

Oceanic and atmospheric management explained that the level of carbon dioxide had been constant before the industrial revolution, 280 parts per million, and that it had remained the same during the previous period of some 6,000 years.

In its statement, the United States Authority noted that today's level was close to that of "4.1 to 4.5 million years ago, when CO2 levels were about 400 ppm or more". At that time, sea level was between 5 and 25 metres higher than today, and vast forests were present in parts of the Arctic, according to studies.