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27 January 2009 at 3:37 am #3527Quote:A new scientific study led by the National Oceanic and Atmospheric Administration reaches a powerful conclusion about the climate change caused by future increases of carbon dioxide: to a large extent, there’s no going back.
The pioneering study, led by NOAA senior scientist Susan Solomon, shows how changes in surface temperature, rainfall, and sea level are largely irreversible for more than 1,000 years after carbon dioxide (CO2) emissions are completely stopped. The findings appear during the week of January 26 in the Proceedings of the National Academy of Sciences.
“Our study convinced us that current choices regarding carbon dioxide emissions will have legacies that will irreversibly change the planet,” said Solomon, who is based at NOAA’s Earth System Research Laboratory in Boulder, Colo.
“It has long been known that some of the carbon dioxide emitted by human activities stays in the atmosphere for thousands of years,” Solomon said. “But the new study advances the understanding of how this affects the climate system.”
The study examines the consequences of allowing CO2 to build up to several different peak levels beyond present-day concentrations of 385 parts per million and then completely halting the emissions after the peak. The authors found that the scientific evidence is strong enough to quantify some irreversible climate impacts, including rainfall changes in certain key regions, and global sea level rise.
If CO2 is allowed to peak at 450-600 parts per million, the results would include persistent decreases in dry-season rainfall that are comparable to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.
The study notes that decreases in rainfall that last not just for a few decades but over centuries are expected to have a range of impacts that differ by region.
Rising sea levels would cause “…irreversible commitments to future changes in the geography of the Earth, since many coastal and island features would ultimately become submerged,” the authors write.
Geoengineering to remove carbon dioxide from the atmosphere was not considered in the study. “Ideas about taking the carbon dioxide away after the world puts it in have been proposed, but right now those are very speculative,” said Solomon.
The authors relied on measurements as well as many different models to support the understanding of their results. They focused on drying of particular regions and on thermal expansion of the ocean because observations suggest that humans are contributing to changes that have already been measured.
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