Global warming gases in the world's atmosphere are rising, with concentrations up 29 percent since the start of the industrial era in 1750, the U.N. weather agency said Monday.
Emissions of carbon dioxide, the most widespread greenhouse gas, were up 39 percent.
The new figures for 2010 from the World Meteorological Organization show that CO2 levels are now at 389 parts per million, up from about 280 parts per million 250 years ago. The levels are significant because the gases trap heat in the atmosphere.
WMO Deputy Secretary-General Jeremiah Lengoasa said CO2 emissions are to blame for about four-fifths of the rise.
He also noted the lag between what gets pumped into the atmosphere and its effect on climate.
"With this picture in mind, even if emissions were stopped overnight globally, the atmospheric concentrations would continue for decades because of the long lifetime of these greenhouse gases in the atmosphere," he said in a statement.
Negotiators from virtually all the world's nations will gather later this month in South Africa to try to agree on steps to head off the worst of the climate disruptions that researchers say will result if concentrations hit around 450 parts per million.
That could happen within several decades at the current rate, though some climate activists and vulnerable nations say the world has already passed what they consider the danger point of 350 parts per million and must somehow undo it.
The WMO said the increase of 2.3 parts per million in CO2 in the atmosphere between 2009 and 2010 shows an acceleration from the average 1.5 parts per million increase during the 1990s.
But there are seasonal fluctuations, too. During the summer growing season, plants absorb carbon dioxide from the atmosphere. In winter, the concentration of C02 rises as vegetation and other biomass decompose.
Since 1750, WMO says, atmospheric concentrations of CO2 have risen 39 percent, those of nitrous oxide have gone up 20 percent and concentrations of methane jumped 158 percent.
Its report Monday cites fossil fuel-burning, loss of forests that absorb CO2 and use of fertilizer as the main culprits.
Nitrogen-based fertilizers are the main source for nitrous oxide, which can trap almost 300 times as much heat as carbon dioxide. Those fertilizers have "profoundly affected the global nitrogen cycle," the report stated.
The impact of fertilizer use is so marked that more nitrous oxide is detected in the northern hemisphere, where more fertilizer is used, than in the south.