Sign of positive feedback that may boost warming

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    Martin W

      From the Independent, re paper appearing in Science:

      The earth's ability to soak up the gases causing global warming is beginning to fail because of rising temperatures, in a long-feared sign of "positive feedback," new research reveals today. Climate change itself is weakening one of the principal "sinks" absorbing carbon dioxide – the Southern Ocean around Antarctica – a new study has found. As a result, atmospheric CO2 levels may rise faster and bring about rising temperatures more quickly than previously anticipated. Stabilising the CO2 level, which must be done to bring the warming under control, is likely to become much more difficult, even if the world community agrees to do it. …

      "The shift that has been detected in a four-year study by researchers from the University of East Anglia, the British Antarctic Survey and the Max-Planck Institute for Biogeochemistry, published in the journal Science, is one of the most ominous in the development of climate change. It implies a breach in the planet's own defences against global warming. Human society has hugely benefited from the earth's natural carbon absorption facility, which means oceans and forests take up roughly half of the CO2 pumped into the atmosphere, in the so-called carbon cycle. What is left in the atmosphere is known as the "airborne fraction". If sinks weakened, the airborne fraction would be likely to get bigger.

      Although supercomputer models of the climate have for some time predicted the weakening of the ocean and terrestrial sinks, no example of it happening has actually been detected – until now. Now the research team has found the vast Southern Ocean, which is the earth's biggest carbon sink, accounting for about 15 per cent of the total absorption potential, has become effectively CO2-saturated. The level of the gas it is absorbing has remained static since 1981 – but in that time the amount emitted has grown by 40 per cent, so it has stopped keeping pace and much more CO2 is left over to trap the sun's heat.

      The effect – revealed by scrutinising observations of atmospheric CO2 from 40 stations around the world, is thought to have been caused by an increase in ocean wind speeds. Stormier weather and stronger waves are churning up the sea and bringing natural CO2 stored there closer to the surface – which reduces the ability of the surface to absorb the gas from the air. The increased winds are believed to be caused by altered atmospheric temperature regimes produced by two separate processes – the depletion of the ozone layer over Antarctica by chlorofluorocarbon gases from aerosol spray cans (now phased out), and global warming. It is thus a positive feedback – an effect of climate change which itself makes climate change worse. …

      Earth's natural defences against climate change 'beginning to fail'

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