The concentration of carbon dioxide (CO2) in the atmosphere is increasing much more rapidly than even the surging economic growth of China and India and the global economy can account for. The reason is a decline in the efficiency of emissions-absorbing "carbon sinks" on land and in the oceans, researchers reported this week in the Proceedings of the National Academy of Science.
About half of the CO2 emissions resulting from human activities are absorbed by natural "sinks," such as forests, other vegetation and the oceans, but this new study shows that the efficiency of these sinks has fallen significantly over the past half century.
Corinne Le Quere, a climate researcher at the British Antarctic Survey, told IPS last May that stronger winds in the Southern Ocean caused by global warming have resulted in it absorbing less and less carbon since 1981. Those winds churn the ocean waters, bringing up more dissolved carbon dioxide from the deep sea to the surface, and consequently less carbon dioxide is absorbed from the atmosphere.
The process is also making the oceans more acidic, threatening coral and other marine life.
"We are depending on carbon sinks like the oceans to absorb a huge amount of our emissions," Le Quere said. "This means there is more urgency than ever to reduce our emissions."
Oceans are also warming, which also reduces their ability to absorb carbon, said Scambos. Warmer North Pacific water is flowing into the Arctic Ocean and is one of the main reasons behind this summer's startling loss of summer sea ice in the Arctic. For the first time in human memory, the fabled Northwest Passage from the Atlantic to the Pacific Ocean was ice-free.
While Arctic sea ice retreats temporarily every summer, this summer the retreat was 2.6 million square kilometres larger than any previous summer's loss..
The big meltdown was outside the range of previous scientific projections, and even worst-case scenarios, said Scambos. It likely represents a new era of accelerated warming over the next few decades, he said. This acceleration may well mean that the Arctic could be completely ice-free in 10 years -- decades faster than previous predications made only a year ago.
Hotter oceans are also statistically correlated with four of the five major extinctions in the past 520 million years of Earth's history, according to a study published Wednesday in the Proceedings of the Royal Society B, a British journal focusing on biological sciences.
Earth is on track to hit this extinction-triggering warming point in about 100 years unless greenhouse gas emissions are curbed, predicts Peter Mayhew of the University of York in Britain.
Another tipping point may have already been reached as warming temperatures appear to have reduced tropical forests' ability to absorb carbon, says a series of new studies published Thursday in the New Scientist magazine. Across the world, from the Amazon rainforest to the Indonesian archipelago, tree growth is slowing down. Rising temperatures, especially at night, have long been predicted to affect forest growth, but no one thought it would begin to affect forests until after global temperatures had risen another 1.5 degrees C.
"It would be terribly worrying if that feedback is already kicking in," said climatologist Rachel Warren from the University of East Anglia in Britain.
The world's tropical forests are estimated to absorb some 15 percent of the carbon that humans are emitting and are considered vital in avoiding catastrophic climate change.
It is not just temperatures that are rising -- plants must also live with higher levels CO2 levels. Scientists at the Smithsonian Tropical Research Institute in Panama have reported faster growing trees, while liana vines have spread 50 to 100 percent in the past 20 years in the Amazon. Unfortunately, these plants absorb much less carbon than the slower growing tropical hardwoods and also kill such trees prematurely. The net effect is that forests will store less carbon, leaving more in the atmosphere, they conclude. Ocean and forest carbon sequestration are crucial factors in climate models. This new revelation that less carbon is being trapped means global average temperatures are going to rise faster and will likely be at the high end of predictions by the Intergovernmental Panel on Climate Change (IPCC) of 2 to 4.5 degrees C for doubling of CO2.
The higher end of this range is not only the most risky, it is the most unpredictable. Once the world comes close to a 4-degree C rise, conditions on the planet will be so different it is nearly impossible to predict when the warming will stop and what impacts it will have, write Myles Allen and David Frame of Oxford University in the Oct. 26 issue of Science magazine.
The main lesson from all this is that policy-makers will not get any better information on how warm it could get, they write.
"With less carbon being captured by the oceans and forests, the future doesn't look good," said Scambos.
The only hope now is major declines in emissions. If millions of people really push for major cuts in emissions, change could happen very fast, he said.
"My biggest worry is that by not acting soon enough, we won't have the resources to do more than keep our heads above water," Scambos concluded.
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