Our home in space

some remarks on global heating and ocean acidity

Guy Ottewell

Sea level

The level of the world ocean is rising because water expands as it warms, and because enormous quantities of ice are melting.
        The level has risen, from 1900 to 2010, 17 centimeters (nearly 7 inches). How much more will it rise by 2100? Probably around a meter.
        That needs some explanation: the estimate has become higher with more study. Climate scientists do not give definite predictions, which would be foolish, but express them as likelihoods. In 2007 the estimate was that the rise would be 18-59 centimeters (meaning a 66% probability of falling within that range). But that estimate, though taking many things into account, did not include the effects of ice dynamics, the movements of icecaps and glaciers, on which there was not yet enough data. When, in 2008, those effects were included, the likely range of the rise increased to 20-200 centimeters.
        Later findings are that the melting rates may be even higher. In 2010 aA geological study in the island of Mallorca showed that sea levels can rise much faster than previously thought: “More disturbing, the record suggests that sea level can go up or down as quickly as two meters a century — nearly 12 times faster than sea-level rise in the past 100 years.”
        Of the planet's ice, 1 percent is on mountain ranges, 9 percent on Greenland, and 90 percent in Antarctica. If they all were to melt, the oceans would rise by 5 meters. That would take centuries to happen, but in 2011 scientists found that the Greenland and Antarctica icecaps are shrinking faster than they expected only a few years earlier.
        Records of tide height have been kept since the 18th century (since 1700 at Amsterdam, for example). A major study in 2010 found that up to 1800 levels actually fell, because of volcanic eruptions cooling the earth; but since 1850 this effect has been overwhelmed by human-caused warming. If this warming had not been offset by the effect of volcanoes, sea levels would now be another 3 inches higher.

200 million people live within one meter of the present sea level, including four-fifths of the world's largest cities.
        Even a slight rise in the ocean causes storm surges to be more catastrophic, especially on low-lying islands. Some island nations will cease to exist. A prominent example is the Maldives. After the 2004 tsunami, 60 percent of this island group was under water. The Maldivian government has bought land in India, expecting to have to move the whole population there. In one of the islands, 60 percent of the residents have volunteered to evacuate within 15 years.
        No wonder that island nations were intensely distressed by the feebleness of the 2009 Copenhagen climate conference. A Fijian delegate broke down in tears as she pleaded for serious measures. The Maldivian president, Mohamed Nasheed, said: “If the Maldives cannot be saved today we do not feel there is much chance for the rest of the world.” And at the end of the conference he addressed the Chinese delegation: “How can you ask my country to go extinct?”
        The huge delta of the Ganges and Brahmaputra rivers, called the Sundarbans, shared by India and Bangladesh, is made up of countless low-lying islands, with a rich ecosystem of mangrove forests sheltering fauna including many of the remaining Asiatic tigers. According to Indian scientists, local sea level had been rising at three millimeters a year, but for 2002-2009 this increased to five millimeters a year, “in accordance with rising temperatures.” cSeveral islands nearby in the Bay of Bengal have been abandoned, thousands of inhabitants becoming “climate-change refugees.” An island called Lohachara was abandoned in 1996; by 2010, 48 per cent of Ghoramara was submerged. The World Wide Fund for Nature warned in February 2010 that the Sundarbans could be swallowed by rising water within 60 years. And the next month satellite photos revealed the disappearance of a two-mile-long island (called New Moore by India and South Talpatti by Bangladesh). At least 10 other islands were said to be at imminent risk.
        Bangladesh as a whole — low-lying, with a dense population of 160 million — is in danger. A one-meter rise in sea level by 2050 would displace 20 million people.