Global Warming Causes Sea-Level Rise and Flooding

Global warming due to anthropogenic greenhouse gas emissions has caused sea level rise. Satellite observations show that since 1990s, sea level has been rising at an annual rate of 3 mm. Sea level is projected to rise at 1.7mm per year in the 20th century, and even faster in the 21st century. IPCC reported rise of 1.2 mm per year between 1993 - 2003, 10 - 20 cm by 2030 and about up to 1 m by the end of the next century. To people living in the low lying areas, vulnerability is increased by the likelihood of storm surges either due to more intense tropical cyclones or mid latitude storms and by other problems such as local land subsidence and the increased intrusion of salt into groundwater.

Changes in mean temperatures and rainfall, and rising sea levels will affect the suitability of land for different types of crops and pasture, the health and productivity of forests, increase the incidences of pests and diseases, affect biodiversity and ecosystems; raise socio economic and resource insecurities.

Sea-level rises due to 4 factors:

- Glacial melting,

- Higher sea temperature,

- Higher evaporation rates from sea
and land

- Heavier rainfalls

Figure shows the mean sea level rise
and future projections
Climate Change 2007 - IPCC

Global warming has increased the melting of ice and glaciers in Arctic sea ice, freshwater ice, ice shelves, the Greenland ice sheet, Alpine and Antarctic Peninsula glaciers and ice caps, snow cover and permafrost.

According to researches at the National Center for Atmospheric Research, even if no more greenhouse gases are added to the atmosphere, global sea-level will rise by four inches over the next century due simply to oceanic thermal expansion, an effect of global warming.

Scientific research indicates that global warming also raises atmospheric and sea temperatures and accelerate water evaporation. This often results in an unbalanced distribution of global rainfall and thus may bring more dry spells and floods, simultaneously in different parts of the world. In China, the frequent drought in the north and floods in the south over recent years reinforce this conclusion.

As reported by BBC news Feb 07 2009 Eastern Australia is facing two extreme weather conditions simultaneously.

According to IPCC report, global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (about 21 000 years ago), stabilized between
2000 - 3 000 years ago. Evidence showed that sea level started to rise from late 19th century.

The rise of sea level has caused more frequent and severe coastal flooding
resulting in loss of coastlines, coastal lands, wetlands and mangroves. The increased severity in floods is projected to bring serious impacts to low-lying areas with high population density. Severe flood may cause large scale population displacement; resulting in socio economic instability and resource insecurity.

In the mega deltas such as Kolkata, Dhaka and Shanghai that are undergoing rapid urbanization. Millions of people will be badly affected in terms of destruction of lives, properties, crops, livelihood means and infrastructures, incurring huge economic losses.

Shanghai, a rapidly urbanized city in the mega delta, has reported a sea level rise of 120 millimeters since 1977 - a level higher than the national average of 90mm, and fastest in history. Many scientists believe rising sea levels are caused by global warming but the city's continuous land subsidence exacerbates the problem. At the same time, the city is sinking by about seven millimeters every year, partly due to the overuse of underground water and the rapid urban construction. (Shanghai Daily Dec 4, 2007)

A man climbs a ladder to reach a drainage sluice station in South China's Guangdong Province June 10, 2007. It was the worst flood to threaten 15 towns of the county in 50 years. [Xinhua News Jun 2007]

Bangladesh has been plagued by floods throughout history. Major flooding recorded in recent years occurred in: 1987, 1988, and 1998; the most devastating one occurred in November 2007.
Cyclone Sidr hit Bangladesh on November 15, 2007 causing massive destruction and extensive live loss in coastal communities

Cyclone Sidr hit Bangladesh on November 15, 2007, causing widespread flooding and massive destruction in coastal communities, with the Red Crescent Society estimating 10,000 of death toll. International groups pledged US$95 million to repair the damage. The flooding has been declared a national calamity by the government.

''Floods in Bangladesh can't be controlled even with all the resources of the world put together,'' President Ershad told the press. ''Even partial protection requires a lot of money, and Bangladesh is a poor country.''

Contrasting a poverty stricken Bangladesh, we now turn to the Netherlands, a developed industrialized country, more than half of which consists of coastal lowlands below sea level. It is one of the most densely populated areas in the world; with more than 55% of the 14 million inhabitants found along coastal mega cities such as Rotterdam, the Hague and Amsterdam. The country has over the years established an elaborate system comprising about 400 km of dykes and coastal dunes to protect it from the sea.

Further reinforcement would just require use of the effects of various forces (tides, currents, waves, wind and gravity) on the sands and sediments so as to create a stable barrier. No new technology will be required against sea level rise next century. Dykes and sand dunes will just need to be raised; though additional pumping will be necessary to combat the intrusion of saline water into freshwater aquifers. An estimate of about USD 12 billion would be required for protection against a sea level rise of 1 m, which is probably within the reach of the country.

The smaller islands are also most exposed to multiple risks which threaten islanders' livelihood. Risks are coastal erosion, coral bleaching, and reduction in fresh water resources. The rising sea water causes intrusion of salt water into fresh water resources, aggravating the existing water-stress problems. Examples are the Maldives in the Indian Ocean, consisting of 1190 individual islands, and the Marshall Islands in the Pacific, which lie almost entirely within 3 m of sea level.

Many scientists warned that the IPCC probably made a far too conservative estimate of sea level rise of 1.7mm per year in the 20th century when it explicitly left out the ice effect. With the earlier than anticipated melting of ice and the shrinking of ice sheets, scientists warned of far greater and much earlier rise of sea level ahead.

The Environment Agency said 2,000 properties between Kingsdown and Pegwell Bay were at risk from flooding.

Figure could rise to 6,000 by 2017 due to climate change and rising sea levels.

Pic: Erosion has affected St Margaret's Bay in Dover in recent years. (BBC Aug 2007)

References and related news:

US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections
Startling new sea level rise research: “Most likely” 0.8 to 2.0 meters by 2100
Sea levels may rise 5 feet by 2100
Report from AGU meeting: One meter sea level rise by 2100 “very likely” even if warming stops?
Sea Level Rise Reports - Impacts of Sea-Level Rise -EPA.
Global Sea Level Change: Determination and Interpretation - AGU
Potential Impacts of Sea-Level Rise on Populations and Agriculture - FAO
Probability of Sea Level Rise - U.S. Global Change Research Office.

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