

Greenhouse gases reached record highs in 2011, says U.N. study

A lignite-fired (brown coal) power plant in Boxberg, Germany.

Story highlights

  • United Nations agency report says 2011 saw new high for levels of greenhouse gases in Earth's atmosphere
  • Levels of carbon dioxide now stand at 390.9 parts per million, up 2 ppm on previous year
  • 375 billion tons of carbon dioxide released into atmosphere since 1750, say WMO
  • Natural carbon sinks are already showing signs of stress and cannot be relied on in future
Carbon dioxide is the single most important greenhouse gas emitted by humans, says the WMO, and the increases recorded last year are in line with average rises seen each year over the last decade.
Combined with average yearly rises of 1.5 ppm during the 1990s, the WMO says radiative forcing (the warming effect on our climate) by long-lived greenhouse gases has now increased 30% since 1990.
"These billions of tons of additional carbon dioxide in our atmosphere will remain there for centuries, causing our planet to warm further and impacting on all aspects of life on Earth," WMO secretary general Michel Jarraud said in a statement.
According to the WMO, about 375 billion tons of carbon has been released into the atmosphere since the industrial revolution began in 1750, with around half this amount being absorbed by carbon sinks. But natural carbon storage facilities like oceans and forests "will not necessarily continue in the future," say the WMO.
"We've already seen that the oceans are becoming more acidic as a result of the carbon dioxide uptake, with potential repercussions for the underwater food chain and coral reefs," Jarraud said in a statement.
The Swiss-based United Nations agency, which uses data from more than 50 countries to compile the report, also detailed rises in other greenhouse gases including methane and nitrous oxide.
Around 60% of methane released into the atmosphere comes from human activities such as farming, rice agriculture, fossil fuel exploitation, landfill and biomass burning, according to the WMO. In 2011, concentrations reached a new high of 1813 parts per billion (ppb), 259% higher than pre-industrial levels.
Emissions of nitrous oxide -- 40% of which are estimated to come from human activity -- reached 324.2 ppb, up one ppb on the 2010 figure and 120% higher than pre-industrial times.
Richard Allan, from the Department of Meteorology at the UK's University of Reading, said the WMO's latest data confirmed the trend in the rate of rise reported in recent decades.
"What it shows isn't surprising, but it obviously has very important implications for the future well-being of the planet," Allan told CNN.
Even if emission rises were halted now, the planet would continue to warm because of the time it takes for the climate system to return to equilibrium, he said.
"We are committed to the warming for a long time, even if we do take strong action against it now," Allan said.