Sea Level Rise

Standard Page - 2006-01-06
"The Maldives is one of the small states. We are not in a position to change the course of events in the world. But what you do or do not do here will greatly influence the fate of my people. It can also change the course of world history." - Statement by H.E. Maumoon Abdul Gayoom (Maldives), in Kyoto, Japan, 3rd Conference of the Parties of the UNFCCC

"The Maldives is one of the small states. We are not in a position to change the course of events in the world. But what you do or do not do here will greatly influence the fate of my people. It can also change the course of world history." - Statement by H.E. Maumoon Abdul Gayoom (Maldives), in Kyoto, Japan, 3rd Conference of the Parties of the UNFCCC

It is not only small island states that need to worry about sea level rise. More than 70% of the world's population lives on coastal plains, and 11 of the world's 15 largest cities are on the coastal estuaries.

A high tide invades Satjellia Island, India, inundating rice paddies and leaving many homes surrounded by water. Scientists estimate that sea level rise will displace over 70,000 people, living effectively on the front line of climate change, from this area by the year 2030.

Over the last hundred years, sea levels rose ten times faster than their 2000-year average, but in the next hundred years the rate of sea level rise could increase dramatically. The IPCC puts predictions of 21st century sea level rise at 9 to 88 cm (3.5-34.6 inches). This may sound relatively small, but even a small amount of sea level rise will wreak havoc on humanity.

What's more, there is growing evidence that melting in Greenland and the Arctic is accelerating. With current warming, it is highly likely that Greenland may melt irreversibly – contributing 7 meters to sea level rise.

How do sea levels rise?

Sea levels will rise as warmer temperatures melt the ice stored in the Antarctica and Greenland. Another equally important cause is the thermal expansion of the oceans – water expands as it heats up.

The amount of sea level rise depends on many variables, including how much the expected increase in precipitation will add to snow packs and, most importantly, our greenhouse gas emissions over the next decades.

It's worth keeping in mind that changes in sea level do not occur uniformly around the globe. Due to ocean circulation and wind pressure patterns, there is actually a fair amount of variation in sea level rise in different parts of the world. The effects of storm surges and spring tides also need to be kept in mind when evaluating sea level rise impacts.

What we can expect

Coastal flooding and storm damage, eroding shorelines, salt water contamination of fresh water supplies, flooding of coastal wetlands and barrier islands, and an increase in the salinity of estuaries – these are all realities of even a small amount of sea level rise. Some low-lying coastal 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 are also at risk.

Greenland at Risk

One frighteningly real possibility is the total melting of Greenland's ice sheet. According to the IPCC, "Climate models indicate that the local warming over Greenland is likely to be one to three times the global average. Ice sheet models project that a local warming of larger than 3°C (5.4°F), if sustained for millennia, would lead to virtually a complete melting of the Greenland ice sheet with a resulting sea-level rise of about 7m" (IPCC 3rd Assessment, Synthesis Report, Summary for Policy Makers).

The Greenland ice sheet is already shrinking and melting. Considering that the IPCC predicts global warming between 1.4 to 5.8°C (2.5-10.4°F), the melting of Greenland seems inevitable – but the question is, by how much?

Broken and drifting sea ice melts in the radiant heat of the Arctic summer, in north Greenland.

And if Greenland begins to melt significantly, the process is irreversible. Even if we manage to reduce emissions, melting will continue until the entire ice sheet vanishes, gradually and inevitably raising sea level over the coming centuries. Under such a scenario, many of the world’s coastal cities, from New York to Bombay, will sink beneath the sea.

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, as the ice shelf was already floating, but it was a dramatic sign of the effects of warming in the area. It's also thought that the ice shelf helped to hold some of the area's land-locked ice in place; with its disappearance, more land ice will fall into the sea over time. The Larsen A ice shelf collapsed in 1995 and was two-thirds as big as Larsen B.

Then in 2005, the British Antarctic Survey released findings that 87% 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 (WAIS) could contribute an additional six metres (20 feet) to sea level rise. Although the chances of this are considered "low" in the IPCC's Third Assessment report, recent research indicates new evidence of massive ice discharge from the WAIS.

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

Consequences

Between the Greenland ice sheet and the Western Antarctic ice sheet, the world could well be facing a 13 metre (43 foot) rise in sea level if we do not drastically reduction our greenhouse gas emissions. Even a small fraction of this would be an economic and humanitarian disaster.

Greenpeace submerges icons of some of the world's most famous buildings and monuments in the sea of Cancun at COP16. The activity is to send a message to the politicians meeting at the UN Climate Summit that the rising tide of climate impacts will affect each and every one of us - rich and poor.

 

A few possible consequences of rising sea levels:

Billions spent on adaptation – if you can afford it. A recent study estimated the costs of adapting to just a one-metre sea level rise in the US would amount to US$156 billion (3% of GNP). Most countries don't have this kind of money to spend.

With only a one-metre sea level rise, some island nations such as the Maldives would be submerged. Already, two of the islands that make up Kiribati (a Pacific island nation) have gone under the waves. In early 2005 other Kiribati islands were inundated by a high spring tide that washed away farmland, contaminated wells with salt water, and flooded homes and a hospital.

If current warming trends continue, cities like London, Bangkok and New York will end up below sea level – displacing millions and causing massive economic damage. At some point, building higher and higher sea walls becomes impractical, and even the wealthiest nations will see cities flood.

Ajit Das lives in Ghoramara Island, India, and is one of the many people affected by sea level rise: "Everything is going under the water. While the edge of the land is breaking in Ghoramara, the middle of the river is becoming shallower. We don't know where we will go or what we will do".

Rising oceans will contaminate both surface and underground fresh water supplies, worsening the world's existing fresh water shortage. Underground water sources in Thailand, Israel, China, Vietnam and some island states are already experiencing salt water contamination.

Rural populations and farmland (especially rice) on some coasts will be wiped out. For example, according to the UK Royal Society, a one-metre sea level rise could flood 17% of Bangladesh, one of the world's poorest countries, displacing tens of millions of people and reducing its rice-farming land by 50%.

There is some good news, though. If we act rapidly to reduce emissions we can still prevent the worst effects of climate change. Revolutionising our energy system, if we do it fast enough, is our only hope to avoid disastrous sea level rise.

Learn more about:

Extreme Weather
Glacier Retreat in the Third Pole
Health, Food and Water
Habitat Loss and Species Extinction

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