Two of the most important greenhouse gases in the Earth's atmosphere reached a record high in 2006, and measurements show that one — carbon dioxide — is playing an increasingly important role in global warming, the U.N. weather agency said Friday.
The global average concentrations of carbon dioxide, or CO2, and nitrous oxide, or N2O, in the atmosphere were higher than ever in measurements coordinated by the World Meteorological Organization, said Geir Braathen, a climate specialist at the Geneva-based agency.
Methane, the third of the three important greenhouse gases, remained stable between 2005 and 2006, he said.
Braathen said measurements show that CO2 is contributing more to global warming than previously.
CO2 contributed 87 percent to the warming effect over the last decade, but in the last five years alone, its contribution was 91 percent, Braathen said. "This shows that CO2 is gaining importance as a greenhouse gas," Braathen said.
The concentration of carbon dioxide in the atmosphere rose by about half a percent last year to reach 381.2 parts per million, according to the agency. Nitrous oxide totaled 320.1 parts per billion, which is a quarter percent higher than in 2005.
Braathen said it appears the upward trend will continue at least for a few years.
The World Meteorological Organization's annual Greenhouse Gas Bulletin provides widely accepted worldwide data on the amount of heat-trapping greenhouse gases in the atmosphere.
Studies have shown that human-produced carbon dioxide emissions heat the Earth's surface and cause greater water evaporation. That leads to more water vapor in the air, which contributes to higher air temperatures. CO2, methane and N2O are the most common greenhouse gases after water vapor, according to the meteorological organization.
They are produced by natural sources, such as wetlands, and by human activities such as fertilizer use or fuel combustion.
There is 36.1 percent more carbon dioxide in the atmosphere than there was in the late 18th century, primarily because of combustion of fossil fuels, the World Meteorological Organization bulletin said.
A report presented by a U.N. expert panel said last week that average temperatures have risen 1.3 degrees Fahrenheit in the last 100 years, and that 11 of the last 12 years have been among the warmest since 1850. Global Warming also led to a sea level increase by an average seven-hundredths of an inch per year since 1961, according to the U.N. Intergovernmental Panel on Climate Change.
The panel's report, which said human activity is largely responsible for global warming, noted that the concentration of carbon dioxide in the atmosphere is far higher than the natural range over the last 650,000 years.
The World Meteorological Organization also concluded that "Greenhouse gases are major drivers of global warming and climate change."
The World Meteorological Organization said it based its findings on readings from 44 countries.
The U.N. Intergovernmental Panel on Climate Change forecast that by 2020, 75 million to 250 million people in Africa will suffer water shortages, residents of Asia's large cities will be at great risk of river and coastal flooding, Europeans can expect extensive species loss, and North Americans will experience longer and hotter heat waves and greater competition for water.