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Global warming

Background - August 24, 2007

Adelie penguin babies, Antarctica.

Global warming

The ocean and its inhabitants will be irreversibly affected by the impacts of global warming and climate change. Scientists say that global warming, by increasing sea water temperatures, will raise sea levels and change ocean currents.

Ocean Currents

The water in our world's oceans is always moving - pulled by tides,blown by waves, and slowly circulating around the globe by the force ofthe Great Ocean Conveyor Belt (also called thermohaline circulation).The Conveyor is powered by differences is water temperature andsalinity, and one of its most well known parts, the Gulf Stream, iswhat gives Europe it's relatively mild climate.

Aside from keeping Europe warm, and playing an important role in theglobal climate, the Conveyor provides an up welling of bottom oceannutrients, and increases the oceanic absorption of carbon dioxide.

What could go badly wrong

Worryingly, recent studies warn that we may already have evidence of aslower Conveyor circulation over the Scotland-Greenland deep oceanridge. And while the Conveyor appears to have operated fairly reliablyover the past several thousand years, an examination of ice cores fromboth Greenland and Antarctica shows that this has not always been thecase. In the more distant past, changes to the Conveyor circulation areassociated with abrupt climate change.

In short, dilution of the ocean's salinity - from melting Arctic ice(such as the Greenland ice sheet) and/or increased precipitation -could switch off, slow down or divert the Conveyor. This dramaticcooling would mean a massive disruption to European agriculture andclimate, and impact other sea currents and temperatures around theglobe.

Sea Level Rise

A global average sea level rise of 9-88 cm (3.5-34.6 inches) isexpected over the next hundred years, thanks to the greenhouse gasseswe have emitted to date and likely future emissions. This will come inroughly equal measure from melting ice and from thermal expansion ofthe oceans (water expands as it heats up).   

Even this comparatively modest projected sea level rise will wreakhavoc.  Coastal flooding and storm damage, eroding shorelines,salt water contamination of fresh water supplies, agricultural areas,flooding of coastal wetlands and barrier islands, and an increase inthe salinity of estuaries are all realities of even a small amount ofsea level rise. Some low lying costal cities and villages will also beaffected.  Resources critical to island and coastal populationssuch as beaches, freshwater, fisheries, coral reefs and atolls, andwildlife habitat is also at risk.

The West Antarctic ice sheet

Only four years ago, it was commonly accepted that the West Antarcticice sheet was stable, but unexpected melting in the region is causingscientists to re-think this assumption.  

In 2002, the 500 billion tonne Larsen B ice shelf, which covered anarea twice the size of greater London, disintegrated in less than amonth. This did not directly add to sea level rise since the ice shelfwas already floating, but it was a dramatic reminder of the effects ofwarming in the area.

Then in 2005, the British Antarctic Survey released findings that 87percent of the glaciers on the Antarctic Peninsula have retreated overthe past 50 years. In the past five years, the retreating glaciers havelost an average of 50 metres (164 feet) per year.   

Potentially, the West Antarctic ice sheet could contribute anadditional six metres (20 feet) to sea level rise. Although thechances of this are considered low in the Intergovernmental Panel onClimate Change's Third Assessment report, recent research indicates newevidence of massive ice discharge from the ice sheet.  

The entire Antarctic ice sheet holds enough water to raise global sea levels by 62 metres (203 feet).

The Greenland glaciers

In July 2005, scientists aboard the Greenpeace ship Arctic Sunrise madea stunning discovery - evidence that Greenland's glaciers aremelting at an unprecedented rate. It's just more evidence that climatechange is no longer on the horizon, it has arrived at our doorstep, andif you live in a coastal city, that's not just a figure of speech.

Findings indicated that the Kangerdlugssuaq Glacier on Greenland's eastcoast could be one of the fastest moving glaciers in the world with aspeed of almost 14 kilometres per year. The measurements were madeusing high precision GPS survey methods. In addition, the glacierunexpectedly receded approximately five kilometres since 2001 aftermaintaining a stable position for the past 40 years.

Greenland's massive ice sheet locks up more than six percent of theworld's fresh water supply, and it is melting much faster thanexpected. If Greenland were to melt fully, it would cause sea levelsaround the globe to rise by nearly 20 feet. Even measurements of fourto five feet of sea level rise could mean that places like New York,Amsterdam, Venice and Bangladesh will experience flooding in low lyingareas.

The alarming retreat of the Kangerdlugssuaq Glacier suggests that theentire Greenland ice sheet may be melting far more rapidly thanpreviously believed. All current scientific forecasts for globalwarming had assumed slower rates of melting. This new evidence suggeststhat the threat of global warming is much greater and more urgent thanpreviously believed.

Habitat Loss

Temperature rises are impacting on the entire marine food web. Forexample, phytoplankton, which feeds small crustaceans including krill,grow under sea ice. A reduction in sea ice implies a reduction in krill- and krill feeds many whale species, including the great whales.

Whales and dolphins strand themselves in high temperatures. The greatwhales also risk losing their feeding grounds, in the Southern Oceanaround Antarctica, because of the melting and collapse of ice shelves.

Whole species of marine animals and fish are directly at risk due tothe temperature rise - they simply cannot survive in warmer waters.Some penguin populations, for example, have decreased by 33 percent inparts of Antarctica, because of habitat decline.

An increasing occurrence of disease in marine animals is also linked to rising ocean temperatures.