Atmospheric volumes of greenhouse gases hit a record in 2013 as carbon dioxide concentrations grew at the fastest rate since reliable global records began, the World Meteorological Organization said on Tuesday.
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"We know without any doubt that our climate is changing and our weather is becoming more extreme due to human activities such as the burning of fossil fuels," said WMO Secretary-General Michel Jarraud in a statement accompanying the WMO's annual Greenhouse Gas Bulletin.
"Past, present and future CO2 emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are non-negotiable," Jarraud said. "We are running out of time."
The volume of carbon dioxide, or CO2, the primary greenhouse gas emitted by human activities, was 396.0 parts per million in 2013, 2.9 ppm higher than in 2012, the largest year-to-year increase since 1984, when reliable global records began.
Methane levels rising
The second most important greenhouse gas, methane, continued to grow at a similar rate to the last five years, reaching a global average of 1824 parts per billion. The other main contributor, nitrous oxide, reached 325.9 parts per billion, growing at a rate comparable to the average over the past decade.
The world has the knowledge and tools to keep global warming within 2 degrees Celsius, a UN goal set in 2010, Jarraud said, which would "give our planet a chance and … our children and grandchildren a future".
"Pleading ignorance can no longer be an excuse for not acting."
The warming effect, or "radiative forcing," measures the net difference between the sunlight that the Earth absorbs and the energy it radiates back into space. More absorption leads to higher temperatures.
After carbon dioxide, methane has the biggest effect on climate. Atmospheric concentrations of methane reached a new high of 1,824 parts per billion in 2013, up 153 per cent from pre-industrial levels of about 700 parts per billion.
About 40 per cent of the methane comes from natural sources such as termites and wetlands, but the rest is due to cattle breeding, rice agriculture, fossil fuel burning, landfills and incineration, according to the agency.