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Oceans on planet Earth have warmed 50 percent faster over the last 40 years due to climate change, Australian and US climate researchers reported Wednesday. Higher ocean temperatures expand the volume of water, contributing to a rise in sea levels that is threatening low-lying, densely-populated coastal countries around the world.
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The study, published in the British journal “Nature”, adds to the growing scientific warning about the speed and results of rising oceans. Rising sea levels are caused by two things: the thermal expansion of sea water (when water heats, it expands), and extra water from melting segments of ice, such as icebergs. Both processes are caused by global warming. The ice sheet that sits on Greenland, for example, contains enough water to raise world ocean levels by seven metres (23 feet), which would completely cover sea-level cities such as Dhaka, The Netherlands and Shanghai.
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Trying to figure out how much each of these factors contributes to rising sea levels is very important to understanding climate change and future temperature rises, scientists say. But up to now, there has been a difference between the computer-based climate models, and the observations of scientists gathering data from the oceans.
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The new study, led by the Centre for Australian Weather and Climate Research, is the first to combine computer based models with scientists’ data. Comparing data from 1961 to 2003 and checking ocean temperatures up to 700 metres (2,300 feet) below the surface, shows thermal warming has resulted in a 0.53 millimetre-per-year rise in sea levels.