Greenhouse gas concentrations in the atmosphere reach new record

to warm. Human activities, such as fossil fuel burning and land use change (for instance, tropical deforestation), are the main sources of the anthropogenic carbon dioxide in the atmosphere. The other main long-lived greenhouse gases are methane and nitrous oxide. Increasing concentrations of the greenhouse gases in the atmosphere are drivers of climate change.

The National Oceanic and Atmospheric Administration’s (NOAA) Annual Greenhouse Gas Index, quoted in the bulletin, shows that from 1990 to 2011, radiative forcing by long-lived greenhouse gases increased by 30 percent, with CO2 accounting for about 80 percent of this increase. Total radiative forcing of all long-lived greenhouse gases was the CO2 equivalent of 473 parts per million in 2011.

Carbon dioxide (CO2)
Carbon dioxide is the single most important greenhouse gas emitted by human activities. It is responsible for 85 percent of the increase in radiative forcing over the past decade. According to WMO’s bulletin, the amount of CO2 in the atmosphere reached 390.9 parts per million in 2011, or 140 percent of the pre-industrial level of 280 parts per million.

The pre-industrial era level represented a balance of CO2 fluxes between the atmosphere, the oceans and the biosphere. The amount of CO2 in the atmosphere has increased on average by 2 parts per million per year for the past ten years.

Methane (CH4)
Methane is the second most important long-lived greenhouse gas. Approximately 40 percent of methane is emitted into the atmosphere by natural sources (for example, wetlands and termites), and about 60 percent comes from activities like cattle breeding, rice agriculture, fossil fuel exploitation, landfills and biomass burning.  Atmospheric methane reached a new high of about 1813 parts per billion (ppb) in 2011, or 259 percent of the pre-industrial level, due to increased emissions from anthropogenic sources.

Since 2007, atmospheric methane has been increasing again after a period of leveling-off with a nearly constant rate during the last three years.

Nitrous oxide (N2O)
Nitrous oxide is emitted into the atmosphere from both natural (about 60 percent) and anthropogenic sources (approximately 40 percent), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. Its atmospheric concentration in 2011 was about 324.2 parts per billion, which is 1.0 ppb above the previous year and 120 percent of the pre-industrial level.  Its impact on climate, over a 100 year period, is 298 times greater than equal emissions of carbon dioxide. It also plays an important role in the destruction of the stratospheric ozone layer which protects us from the harmful ultraviolet rays of the sun.