Rise in CO2 levels is outpacing fossil fuel use, suggesting planet's natural ability to soak up emissions may be slowing
* Carbon dioxide levels grow at fastest rate on record
* Ocean acidification rises at fastest rate in 300 million years
* Planet may be losing ability to absorb emissions - WMO
(Adds quotes from news conference, data on ocean acidification and absorption)
By Tom Miles
GENEVA, Sept 9 (Reuters) - The amount of greenhouse gases in the atmosphere reached a record high in 2013 driven by a surge in the level of carbon dioxide, the World Meteorological Organization said on Tuesday, urging international action to combat climate change.
"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 to accompany the WMO's annual Greenhouse Gas Bulletin.
The rise in carbon dioxide (CO2) levels is outpacing fossil fuel use, implying that the planet's natural ability to soak up emissions of the gas may be slowing down, the report said.
"It may be due to the reduced uptake of CO2 by the biosphere," Jarraud told a news conference, but said more research was needed. "If that is confirmed, it is of significant concern."
The biosphere, including plants and soil, and the oceans each absorb about 25 percent of human CO2 emissions. If that ratio falls, more of the planet-warming gas will remain in the atmosphere, where it can stay for hundreds of years.
The ocean is getting rapidly more acidic, impairing its ability to absorb carbon dioxide. The rate of ocean acidification is unprecedented at least over the past 300 million years, the WMO said.
"The total change of ocean acidity since pre-industrial (times)... is 25 percent, and 6 percent was done within the last 10 years," said WMO scientific officer Oksana Tarasova.
Even if human-made carbon emissions fall by 80 percent by 2050, the total warming effect of greenhouse gases in the atmosphere will have barely receded by 2100. The longer fossil fuel use grows, the harder it will be to reverse the warming effect, the WMO said.
"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, the main greenhouse gas emitted by human activities, was 396.0 parts per million (ppm) in 2013, 2.9 ppm higher than in 2012, the largest year-to-year increase since 1984, when reliable global records began.
Methane, the second most important greenhouse gas, continued to grow at a similar rate as the last five years, reaching a global average of 1824 parts per billion (ppb). The other main contributor, nitrous oxide, reached 325.9 ppb, growing at a rate comparable to the average over the past decade.
Greenhouse gas emissions are rising mainly due to industrial growth in China, India and other emerging economy nations. Almost 200 governments have agreed to work out a deal to limit global warming at a summit in Paris next year.
The world has the knowledge and tools to keep global warming within 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times, a U.N. goal set in 2010, Jarraud said, which would "give our planet a chance and ... our children and grandchildren a future".
The U.N.'s panel of climate scientists says it is at least 95 percent probable that human activities are the main driver of global warming since 1950. But voters in many countries are doubtful, suspecting that natural variations are to blame.
(Reporting by Tom Miles; Editing by Janet Lawrence)
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