The main global warming pollutant reached a record high level in the air in 2011, the U.N. weather agency said Tuesday.
Concentrations of heat-trapping carbon dioxide in the atmosphere averaged 390 parts per million during the year. That is up 40 percent from before the Industrial Age, when levels were about 280 parts per million, the World Meteorological Organization said.
Carbon dioxide, the chief greenhouse gas, stays in the atmosphere for 100 years. Some of it is natural, coming mainly from decomposing dead plants and animals, but scientists say the bulk of it is from the burning of fossil fuels.
There have been 350 billion metric tons of carbon dioxide added to the atmosphere since 1750 and it "will remain there for centuries, causing our planet to warm further and impacting on all aspects of life on earth," said WMO Secretary-General Michel Jarraud. "Future emissions will only compound the situation."
Between 1990 and 2011, carbon dioxide and other gas emissions caused a 30 percent increase in the warming effect on the climate, the agency reported.
After carbon dioxide, methane has the biggest effect on climate. Atmospheric concentrations of methane also reached a new high of 1,813 parts per billion in 2011, up 159 percent from pre-industrial levels of about 700 parts per billion. About 40 percent comes from natural sources such as termites and wetlands, but the rest is due to cattle breeding, rice agriculture, fossil fuel burning, landfills and incineration, the agency said.