Global warming

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 of the Great Ocean Conveyor Belt (also called thermohaline circulation). The Conveyor is powered by differences is water temperature and salinity, and one of its most well known parts, the Gulf Stream, is what gives Europe it's relatively mild climate.

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

What could go badly wrong

Worryingly, recent studies warn that we may already have evidence of a slower Conveyor circulation over the Scotland-Greenland deep ocean ridge. And while the Conveyor appears to have operated fairly reliably over the past several thousand years, an examination of ice cores from both Greenland and Antarctica shows that this has not always been the case. In the more distant past, changes to the Conveyor circulation are associated 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 dramatic cooling would mean a massive disruption to European agriculture and climate, and impact other sea currents and temperatures around the globe.

Sea Level Rise

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

Even this comparatively modest projected sea level rise will wreak havoc.  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 in the salinity of estuaries are all realities of even a small amount of sea level rise. Some low lying costal cities and villages will also be affected.  Resources critical to island and coastal populations such as beaches, freshwater, fisheries, coral reefs and atolls, and wildlife habitat is also at risk.

The West Antarctic ice sheet

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

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

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

Potentially, the West Antarctic ice sheet could contribute an additional six metres (20 feet) to sea level rise. Although the chances of this are considered low in the Intergovernmental Panel on Climate Change’s Third Assessment report, recent research indicates new evidence 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 made a stunning discovery - evidence that Greenland’s glaciers are melting at an unprecedented rate. It's just more evidence that climate change is no longer on the horizon, it has arrived at our doorstep, and if you live in a coastal city, that's not just a figure of speech.

Findings indicated that the Kangerdlugssuaq Glacier on Greenland's east coast could be one of the fastest moving glaciers in the world with a speed of almost 14 kilometres per year. The measurements were made using high precision GPS survey methods. In addition, the glacier unexpectedly receded approximately five kilometres since 2001 after maintaining a stable position for the past 40 years.

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

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

Habitat Loss

Temperature rises are impacting on the entire marine food web. For example, 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 great whales also risk losing their feeding grounds, in the Southern Ocean around Antarctica, because of the melting and collapse of ice shelves.

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

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