GENEVA — Greenhouse gases in the Earth’s atmosphere have reached record highs and show no sign of leveling off, the U.N. weather agency said Tuesday.
Major greenhouse gases have been increasing every year since detailed records started being kept in 1998 and follow a trend of rising emissions that began with the Industrial Revolution in the mid-18th century.
The report by the World Meteorological Organization was released a year before representatives from major countries meet in Copenhagen, Denmark, to negotiate a new international treaty to curb greenhouse gases for 2012 and beyond.
The gases — carbon dioxide, or CO2; nitrous oxide, N2O; and methane — are produced partially by natural sources, such as wetlands, and partially by human activities such as fertilizer use or fuel combustion.
“CO2 and N2O are increasing steadily … and there is no sign of leveling off,” said Geir Braathen, a climate specialist at the Geneva-based agency. Methane also has been rising, but its growth had been slowed until last year.
Carbon dioxide was up most in 2007, the latest year for which figures are available. It increased to 383.1 parts per million, one-half percent more than the 2006 amount. Methane and nitrous oxide rose by lesser amounts, the WMO said.
Nitrous oxide increased by 0.25 percent over the previous year to 320.9 parts per billion.
Methane concentrations in the atmosphere soared to the highest annual increase measured since 1998, Braathen said. The gas was at 1,789 parts per billion last year — a 0.34 percent increase from 2006.
Braathen said that it was too soon to say what had caused the increases.
The WMO’s annual Greenhouse Gas Bulletin 2007 provides widely accepted worldwide data on the amount of heat-Âtrapping greenhouse gases in the atmosphere.
That leads to more water vapor in the air, which contributes to higher air temperatures.
Studies have shown that human-produced carbon dioxide emissions heat the Earth’s surface and cause greater water evaporation. A Nobel prize-Âwinning panel of U.N. scientists has said emissions must level off within the next 10 to 15 years and then start to dramatically decline to avoid a rise in average temperatures that could have catastrophic consequences, such as severe drought and flooding.
CO2, methane and N2O are the most common greenhouse gases after water vapor, the WMO said.
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