Green House Gases Other than CO2
Carbon dioxide remains the largest by mass of potential green house gases affecting climate change, but other greenhouse gases measurably contribute to the problem. A new study, conducted by NOAA scientists and published online today in Nature, shows that cutting emissions of those other gases could slow changes in climate that are expected in the future. Discussions with colleagues around the time of the 2009 United Nations’ climate conference in Copenhagen inspired three NOAA scientists — Stephen Montzka, Ed Dlugokencky and James Butler of NOAA’s Earth System Research Laboratory in Boulder, Colo. — to review the sources of non-carbon dioxide (CO2) greenhouse gases and explore the potential climate benefits of cutting their emissions.
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be much colder than at present.
Water vapor and clouds also have a profound effect on climate but are not easily controlled.
Scientists know that stabilizing the warming effect of CO2 in the atmosphere would require a decrease of about 80 percent in human-caused CO2 emissions — in part because some of the carbon dioxide emitted today will remain in the atmosphere for thousands of years. In contrast, cutting all long-lived non-CO2 greenhouse gas emissions by 80 percent could diminish their combined climate warming effect substantially within a couple of decades. Cutting both CO2 and non-CO2 greenhouse gas emissions to this extent could result in a decrease in the total warming effect from these greenhouse gases this century, the new paper shows.
For the new analysis, the researchers considered methane; nitrous oxide; a group of chemicals regulated by an international treaty to protect Earth’s ozone layer; and a few other extremely long-lived greenhouse gases currently present at very low concentrations.
The new review paper describes the major human activities responsible for these emissions, and notes that steep cuts (such as 80 percent) would be difficult. Without substantial changes to human behavior, emissions of the non-CO2 greenhouse gases are expected to continue to increase.
The climate-related benefits of reductions in non-CO2 greenhouse gases have limits, Montzka and his colleagues showed. Even if all human-related, non-CO2 greenhouse gas emissions could be eliminated today, it would not be enough to stabilize the warming influence from all greenhouse gases over the next 40 years — unless CO2 emissions were also cut significantly.
The scientists also noted in the paper the complicated connections between climate and greenhouse gases, some of which are not yet fully understood. The non-CO2 gases studied have natural sources as well as human emissions, and climate change could amplify or dampen some of those natural processes, Dlugokencky said. Increasingly warm and dry conditions in the Arctic, for example, could thaw permafrost and increase the frequency of wildfires, both of which would send more methane and carbon dioxide into the atmosphere.
For further information: http://www.noaanews.noaa.gov/stories2011/20110803_nonco2.html