Global warming real say new studies
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.
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.
Greenhouse gases 'do warm oceans'
BBCNews.com, Feb. 18, 2005
Scientists say they have "compelling" evidence that ocean warming over the past 40 years can be linked to the industrial release of carbon dioxide.
US researchers compared the rise in ocean temperatures with predictions from climate models and found human activity was the most likely cause.
In coming decades, the warming will have a dramatic impact on regional water supplies, they predict.
Details of the study were released at a major science meeting in Washington DC.
The conference is the annual gathering of the American Association for the Advancement of Science (AAAS).
"This is perhaps the most compelling evidence yet that global warming is happening right now and it shows that we can successfully simulate its past and likely future evolution," said lead author Tim Barnett, of the climate research division at the Scripps Institution of Oceanography in San Diego, California.
"If you take this data and combine it with a decade of earlier results, the debate about whether or not there is a global warming signal here and now is over at least for rational people."
The team fed different scenarios into computer simulations to try to reproduce the observed rise in ocean temperatures over the last 40 years.
They used several scenarios to try to explain the oceanic observations, including natural climate variability, solar radiation and volcanic emissions, but all fell short.
"What absolutely nailed it was greenhouse warming," said Dr Barnett.
This model reproduced the observed temperature changes in the oceans with a statistical confidence of 95%, conclusive proof - say the researchers - that global warming is being caused by human activities.
Regional water supplies will be dramatically affected by climate change in the decades immediately ahead, say the team.
The western US is already experiencing water shortages and research suggests that the region could face a water crisis within 20 years.
In the South American Andes and western China, millions of people could be left without adequate water during the summer due to accelerated melting of glaciers.
"If the snow pack melts sooner, and if societies don't have the ability catch all of that water, they're going to end up with water shortages in the summer," Dr Barnett explained.
According to the Scripps researcher, political leadership was now needed to avert a global disaster.
"Hopefully we can get the US cranked around in that direction. I think the first thing to do is figure out the global warming-related problems we have ahead of us around the world.
"Unless we know what we're dealing with, I think it's going to be pretty hard to fix it."