Current sea level rise
Since the mid-19th century - in global terms - a significant rise in sea level observed, which has been lying alone in the 20th century at about 17 cm. The average sea level rise for the period 1901-2010 is given in the Fifth Assessment Report of the IPCC with 19 ± 2 cm. Since 1993, the sea level will rise by an average of 3.2 mm per year.
A cause of the increase is probably the global warming. Global warming leads to sea level rise for two reasons: First, it is due to the heating of the oceans for the thermal expansion of the water, which consequently takes up more volume. Second, increased air temperatures lead to loss of land ice in the form of glaciers or ice sheets, which brings additional water into the oceans. To what extent secular effects play (eg the Geodynamics or a counter movement to the " Little Ice Age " in 1850 ) is still unclear in detail.
Some new research results can be up to 2100 a sea level rise of at least one -half to two meters expected. Within 300 years, an increase of 2.5 m to 5.1 m is possible.
Sea level rise threatens particularly island states and countries with wider coastal area as well as a low-lying hinterland, such as Bangladesh and the Netherlands. Here poorer States are at risk significantly more than wealthy industrialized countries that can not afford costly coastal protection measures. Effective coastal protection costs significantly less - in most cases less than 0.1 percent of GDP - than repairing the damage resulting from inactivity.
Historical review
In the past, there have been enormous changes in sea level. Here is a close relationship between the global temperature and sea level. In the long run, a change in the average global temperature by 1 ° C with a changing sea levels by 10 to 20 m is connected.
The last time the Earth was in front of about 35 million years ago, during the Eocene free of polar ice caps. The sea level at that time was almost 70 m higher than today. Prior to about three million years ago, during the Pliocene, the northern hemisphere was free of ice, the average climate was about 2-3 ° C warmer than today, and sea levels were 25 to 35 m higher than today. During the last interglacial, the Eemian interglacial period about 120,000 years ago, the climate about 1 to 2 ° C warmer than today, and sea level was four to six meters accordingly higher than today. At that time, the sea level rose very rapidly by an average of 1.6 m per century on. Because Greenland has contributed most of the former sea-level rise, this indicates a nearly complete melting of the ice sheet there within 400 years.
In the subsequent cold period, the sea level fell to the climax of this glaciation about 20,000 years ago to a level around 120 m lower than today. The average global temperature at that time was 5 to 6 ° C. lower than today. At the transition to the current warm period, the Holocene, the sea level rose over the course of millennia steeply. About 8,000 years ago slowed the increase to come almost to a stop about 2,000 years ago. Until the beginning of the industrialization of the sea level rose then no longer, or at most by 0.2 mm per year.
Rise in the recent past
Since industrialization, and thus since the beginning of man-made global warming to today, sea level rise has accelerated significantly. Throughout the 18th century, it increased by only 2 cm, in the 19th century by 6 cm, and in the 20th century already by 19 cm.
Between 1840 and 2001 an increase of the water level on the North Sea coast of 23 cm was determined. Between 1870 and 2004, the sea level has risen by about 19.5 cm, the average increase was measured in the 20th century, 1.7 ± 0.5 mm per year and 1961-2003 yearly 1.8 ± 0.5 mm. The increase may have been underestimated during the 20th century. If the amounts of water that were retained in increasingly behind dams in the calculation, the result for the period 1930-2007 with a calculated increase of 2.46 mm per year.
Since the 1990s, the increase accelerated considerably. Between 1993 and 2007, an average annual increase of 2.9 ± 0.4 mm could be detected with the help of satellites. According to the Australian Commonwealth Scientific and Industrial Research Organisation ( CSIRO ), the increase from 1992 to 2009 amounted to an average of 3.3 mm per year, about 50 % more than were measured even in the whole of the 20th century.
Causes
Between 1961 and 2003 the rate of increase in sea level was 1.8 ± 0.5 mm per year. Of these, 0.42 ± 0.12 mm per year of thermal expansion of the oceans and 0.50 ± 0.18 mm melting glaciers and ice caps are attributed. On the account of the Greenland ice sheet to go 0.05 ± 0.12 mm and on the the Antarctic ice sheet 0.14 ± 0.41 mm. As the sum result 1.1 ± 0.5 mm per year, a difference of 0.7 ± 0.7 mm for the observed increase.
Between 1993 and 2003, the mean increase was 3.1 ± 0.7 mm per year. 1.6 ± 0.50 mm by the thermal expansion, 0.77 ± 0.22 mm from dwindling glaciers and ice caps and 0.21 mm by the Greenland ( uncertainty ± 0.07 mm) and Antarctic (± 0, 35 mm) ice sheet caused. The total, 2.8 ± 0.7 mm, deviates by 0.3 ± 1.0 mm from the observed increase.
Between 2003 and 2008 found a continued strong medium sea level rise at a rate of 2.5 mm per year instead, the warming of the oceans is, however, in a plateau phase and contributes only 0.4 mm to the increase in; therefore results in the vast majority of the increase by 1.9 mm from the melting of continental ice sheets since then.
In 2011, the contribution of melting ice sheets was examined to sea level rise in a study that was in the analyzes in combination of different measurement methods to minimize the error of the period from 1992 to 2009 and came to the following results: In 2006, the Arctic and Antarctica together lost 475 gigatons of ice, which roughly corresponds to the amount of water of Lake Erie and this year led to a sea level rise of 1.3 mm. The melting of ice caps and glaciers contributed in the same year with a lot of additional 402 gigatons in to further sea level rise. The melting rate shows a sharp rise: Over the period 1992 to 2009 went to the Arctic and Antarctica together every year 36 gigatons of ice lost more than the year before. For comparison, in Lake Constance are 48 gigatons of water.
In the event that continues this momentum, the sea level would by 2050 to 32 cm rise (15 cm from the melt in the Arctic and Antarctic, 8 cm from the melt of glaciers and ice caps, 9 cm from the thermal expansion of sea water ).
Future increase
According to various scenarios of the Intergovernmental Panel on Climate Change (IPCC ), published in his 2007 Fourth Assessment Report, the sea level could be up to the period 2090-2099 compared with the period 1980 to 1999 the global average between 0.18 m and 0.59 m increase. Since the publication of the most recent IPCC report, however, some studies have appeared that hold the figures given there for an underestimate. In different methodological approaches, the authors expect by the end of 21st century sea-level rise from 0.5 to 1.9 m. From the year 2050, at Grinsted et al. assumed an annual increase of 1 cm. Under physically possible, but extreme conditions, a maximum increase of 2 m is considered possible.
Against the background of similar rapid increases during the Eemian interglacial period 120,000 years ago, such estimates are realistic. It should be noted that the increase will not make anywhere uniformly noticeable in the world. Due eustatischer fluctuations are for the North Pacific and the U.S. Coast adopted significantly higher values than the global average.
If the heating at 3 ° C stabilized above pre-industrial value, a sea level rise is projected to the year 2300 by 2.5 to 5.1 m. This would benefit 0.4 to 0.9 m by the thermal expansion, 0.2 to 0.4 m by the melting of mountain glaciers, 0.9 to 1.8 m due to the melting of the glaciers of Greenland and 1 to 2 m by the contributed melting of the glaciers of West Antarctica.
A complete melting of the Greenland ice sheet would raise sea level by about 7.3 m. Currently, it is anticipated that this process would take at least several hundred years. At about the same amount would have increased the oceans from melting of the Greenland principle also applicable with unstable West Antarctic ice sheet. The 25.4 million km ³ of ice around the Antarctic would even lead to an increase of about 57 m. The world's glaciers contain nearly 160,000 with a volume of 80,000 cubic kilometers about as much water as the ice caps ( 100,000 km ³) and so could raise sea level by 24 cm ( ice caps: 27 cm) can rise. The thermal expansion contributes per degree Celsius warming by 20 to 40 cm for sea level increase.
The melting icebergs floating in water wearing only slightly to rising sea levels at: Would melt any floating ice, the sea level would rise by about 4 cm. The thermal expansion is driven by the self heating of the deep water on, which is caused by the mixing of warm surface water with cooler water from deeper layers. Although effective climate helps the air temperatures to stabilize, must for the oceans a delayed onset stop the temperature increases are adopted by several centuries, within which nothing can be changed on the thermal component of sea level rise. Even with immediate onset of effective climate protection, the rise in sea level would be barely slowed down in the coming decades.
Direct threats and countermeasures
The effects of sea level rise can be broadly classified into five categories:
- Erosion of beaches and cliffs,
- Increased flood and storm damage,
- Flooding of low-lying areas,
- Elevated groundwater levels and
- Saltwater intrusion in groundwater and surface water.
The rise in sea level poses particular risks for residents of coastal regions and cities. Among the countries that are most vulnerable to sea-level rise, including Bangladesh, Egypt, Pakistan, Maldives, Indonesia and Thailand, all of which have a large and relatively poor population. To live, for example, in Egypt around 16 % of the population (about 12 million people) in an area that would be flooded even with a rise in sea level of 50 cm, and in Bangladesh live more than ten million people is not higher than 1 m above sea level. In a sea level rise of 100 cm would not only them, but a total of 70 million people to be resettled in Bangladesh if the country does not invest in coastal protection measures. It would also be halved by the loss of land and the increase of salt content in the soil, the rice harvest.
Without countermeasures, 150,000 km ² land area would be at a sea level rise of 1 m around the world are permanently flooded, of which 62,000 km ² of coastal wetlands. 180 million people would be affected, and 1.1 trillion dollars in destroyed property would be expected (with today's population and acquis ). According to the OECD people increased to 2,070 the number of people in coastal megacities, which are threatened by a statistically occurring once in a hundred years flood event, from about 40 million in 2005 to 150 million then. This applies to an assumed increase in sea level of 0.5 m. While the risk is present in economic damages in the 136 investigated port cities at $ 3 trillion, this value in the next 60 years is expected to increase more than tenfold to $ 35 trillion, while coastal protection measures, of course, can significantly reduce this risk.
Especially some small countries in the Pacific Ocean have to fear that they sink due to their very low level in the coming decades in the sea, if the increase is not slowing down. The archipelago of Tuvalu has become popular in this context, since its highest point is only five meters above sea level, and therefore it is considered as particularly vulnerable. Also affected are located at sea level holms the German North Sea that are at risk in the long term in their existence.