Atmospheric CO2 and Methane Still Building

NOAA The graph shows recent monthly mean carbon dioxide measured at the Mauna Loa Observatory, Hawaii (recent months are preliminary data).

The National Oceanic and Atmospheric Administration is reporting that the concentrations of carbon dioxide and methane, the two most important greenhouse gases released through human activities, rose in 2008.

The agency’s preliminary summary of greenhouse gas trends consolidates data from 60 monitoring stations around the world. A variety of factors shapes how much of these two gases remains in the atmosphere after they are emitted, which is one reason the global economic recession hasn’t become evident in the data yet, N.O.A.A. researchers said.

The concentration of carbon dioxide has reached 386 parts per million in the air. The pre-industrial peak in concentrations was 280 parts per million (UPDATE: for at least the preceding 650,000 years or so). Some scientists, notably  James Hansen of NASA, say that a long-term target for the atmospheric concentration of the gas should be 350 parts per million. In this century, given continuing growth in the use of fossil fuels, many climate scientists see the concentration exceeding 450 parts per million or even 550 parts per million before stabilizing and — someday, perhaps — declining.

Methane levels rose in 2008 for the second consecutive year after a 10-year plateau. As the agency put it, “Atmospheric concentrations increased by 4.4 molecules for every billion molecules of air, bringing the total global concentration up to 1788 parts per billion.” Methane persists only a few years in the air, but is about 25 times more efficient than carbon dioxide at trapping heat.

In a printed statement, Pieter Tans of the agency’s Earth System Research Laboratory in Boulder, Colo., said the only way to stop growth in the atmospheric concentration of the gases is to reduce emissions enough that natural processes can keep pace. “Think of the atmosphere and oceans taking in greenhouse gases as  a bathtub filling with more water than the drain can empty, and the drain is very slow,” Dr. Tans said.