A leading US team of climate researchers on Friday released “the most compelling evidence yet” that human activities are responsible for global warming. They said their analysis should “wipe out” claims by sceptics that recent warming is due to non-human factors such as natural fluctuations in climate or variations in solar or volcanic activity.
Scientists from the Scripps Institution of Oceanography in California have been working for several years with colleagues at Lawrence Livermore National Laboratory to analyse the effects of global warming on the oceans. They combined computer modelling with millions of temperature and salinity readings, taken around the world at different depths over five decades.
The researchers released their conclusions on Friday at the American Association of the Advancement of Science meeting in Washington. They found that the “warming signals” in the oceans could only have been produced by the build-up of man-made carbon dioxide in the atmosphere. Non-human factors would have produced quite different effects.
Pressure on Bush to address global warming
The latest study to suggest that global warming is a real phenomenon, and one caused by human action, adds further weight to a body of scientific evidence that has been accumulating steadily.
Tim Barnett, the Scripps project leader, said previous attempts to show that human activities caused global warming had looked for evidence in the atmosphere. “But the atmosphere is the worst place to look for a global warming signal,” he said. “Ninety per cent of the energy from global warming has gone into the oceans and the oceans show its fingerprint much better than the atmosphere.”
Prof Barnett added: “The debate over whether there is a global warming signal is over now at least for rational people.” He urged the US administration to rethink its refusal to join the Kyoto Protocol, which took effect this week.
The Scripps scientists also looked at the likely climatic effects of the warming they observed. They highlighted the impact on regional water supplies, which would be severely reduced during the summer in places that depend on rivers fed by melting winter snow and glaciers such as western China and the South American Andes.
The conference also heard a gloomy analysis of the way the North Atlantic Ocean is reacting to global warming from Ruth Curry of Woods Hole Oceanographic Institution in Massachusetts. Her new study showed that vast amounts of fresh water more than 20,000 cubic kilometres have been added to the northernmost parts of the ocean over the past 40 years because the Arctic and Greenland ice sheets are melting.
According to Dr Curry, the resulting change in the salinity balance of the water threatens to shut down the Ocean Conveyor Belt, which transfers heat from the tropics towards the polar regions through currents such as the Gulf Stream. If that happened, winter temperatures in northern Europe would fall by several degrees.
The possible failure of the North Atlantic conveyor has been discussed for several years and was fictionalised last year in the film The Day After Tomorrow. Dr Curry said the accumulation of freshwater in the upper ocean layers since the 1990s meant that the risk should be taken seriously.
