The level of the world ocean is rising because water expands as
it warms, and because enormous quantities of ice
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
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.