what does global warming do to sea levels

Abstract

Around 250 million people live by the coast, less than five m above the ocean. Changes in sea level bear on people through flooding, when water in rivers cannot menstruation into the sea because the sea is too high and when seawater surges onto the state during storms. If the body of water water finds its way to farms and reservoirs, it tin harm our drinking water and our ability to abound crops. Because of this, cognition of how and why sea level is changing is of importance to society.

How Much is Sea Level Changing?

Over the last 150 years, regular measurements take been made of the tides in ports beyond the earth and these measurements tell u.s.a. how global sea level has inverse. As you can see in Figure 1, the first measurements were very elementary and had some errors. But, in more than recent times, the accuracy of sea level measurements has improved, and in the past few decades, we have been able to use satellites to take highly accurate measurements of the world's oceans [i, two]. The information gathered shows that, since most 1850, sea level has risen by about 20 cm around the world. The rate of ocean level ascension (how quickly it is rising) has also grown over this fourth dimension, to just over 3 mm each year since the year 2000 [3].

• Figure i - Global sea level change since the 1850s [ane, 2].
• The y-axis shows the ocean level change in centimeters; the x-axis is the date in years. Although the early measurements were quite elementary and lacked accurateness, they reveal an upward trend in sea level (virtually 0.8 mm every year) that is greater than the margin of error. Past the mid 1900s, measurements became much more accurate (the blue line) and showed the rate of sea level rise to take increased to effectually two mm per yr. In the last few decades satellite measurements (the blackness line) take provided highly authentic records of body of water level and showed the rate of sea level rise today stand at just over 3 mm each year.

Why Does Sea Level Alter?

In that location are four main ways that bounding main level can rising: (i) Ocean warming due to global warming causes sea level to rise because water expands as it warms up; (2) melting of the world'due south water ice sheets in Greenland and Antarctica; (three) melting of smaller glaciers around the world; and (4) subtract in the amount of water held on state, for example, in groundwater beneath the state and in reservoirs above the country. Body of water warming accounts for effectually half of the observed modify in sea level (this is often chosen "thermal expansion"), with the melting of thousands of minor glaciers bookkeeping for the other half of the increase in bounding main level. Since the 1800s, the melting ice sheets in Antarctica and Greenland take contributed relatively little to sea level change. But, these ice sheets are starting to melt faster due to global warming and may push sea level upwardly much more in the future.

How Much Could Bounding main Level Rise?

Because of global warming, the thermal expansion of the body of water and glacier melting volition proceed to play a function in the ascent of ocean level in the future [3]. If all of the planet'southward remaining every bit small-scale glaciers were to melt, bounding main level would rise nearly 50 cm. The corporeality that thermal expansion can raise sea level in the future will depend on the continued warming of ocean water. The largest possible contribution to sea level ascent in the future comes from the world's large ice sheets in Greenland, West Antarctica, and East Antarctica. If these ice sheets melted completely, the level of the oceans would ascent about 7 m from the Greenland ice sheet, 5 thousand from the West Antarctic ice sail, and 53 m from the East Antarctic water ice sheet. This is why many glaciologists (scientists who report ice) focus on how Greenland and Antarctica are changing because of global warming.

How Tin can Melting Ice Sheets Contribute to a Rise in Body of water Level?

As shown in Figure 2, the three ice sheets of W and East Antarctica and Greenland are each different and react differently to global warming likewise. For Greenland, much of the ice melting comes from warm air meeting the ice, turning the ice into water which then runs off into the sea. In Due west Antarctica, the ice canvas is resting on a bed of earth that is over 2 km beneath sea level in some places, making information technology known equally a "marine" ice sheet. Every bit the body of water is in contact with the water ice sheet border, the warmth of the ocean water next to the ice will determine whether, and how much, the ice sheet melts. In East Antarctica, the bulk of the water ice rests on land to a higher place sea level. While the intense cold of East Antarctica means that this water ice sheet has probable been around for as long equally 14 meg years, the huge size of this ice sheet ways that if fifty-fifty a minor percentage of the ice sheet melts, there could be meaning sea level effects for the whole world.

• Figure 2
• A. Water ice loss in Greenland through direct melting of ice, caused by warm air, and run-off of the h2o into the body of water. B. Satellite measurements of ice surface elevation change in Greenland, showing the zones of major ice sheet loss (in red)—the boxes show where almost melting occurs. C. Satellite measurements of ice surface elevation change in Antarctica. The red colors show where ice is beingness lost, and the box shows where this is happening nigh. D. Water ice loss in Antarctica, through bounding main-driven melting of the ice sail and floating water ice shelves . In Antarctica, the warm ocean flows below the floating ice shelf, causing it to melt from its underside, which leads to farther loss of the grounded function of the ice sheet.

In all water ice sheets, ice flows slowly from the heart to the edges, where the water ice is lost to the body of water, either past melting or through the breaking of icebergs. This water ice loss is balanced by snowfall accumulation at the surface of the water ice sail. The difference between the ice that is lost and the amount of snow that accumulates will determine how much the water ice sheet affects sea level modify. Withal, changes to the way the ice flows, whether the flow speeds up or slows down, can likewise lead to rapid changes in the amount of ice that ends up in the ocean. So, changes in the way ice flows can besides affect sea level modify.

In W Antarctica and parts of Eastward Antarctica, the ice that rests on country is surrounded by floating ice shelves several hundred meters thick. These floating shelves act as "buttresses" to the grounded water ice, keeping it in place. So, fifty-fifty though melting of the floating ice shelves would not contribute straight to sea level, considering they take already displaced their own weight in water, if they melt the grounded ice upstream will lose its back up, which could result in increased ice menses, meaning more than ice would cease upward in the ocean and ocean level would rise.

Incidentally, ice sheets and ice shelves should not be confused with sea water ice , which is a very thin (1–2 m) layer of ice over the cold polar ocean. In the Arctic, the sea ice has been shrinking for several decades equally a issue of global warming. Like ice shelves, sea water ice is afloat in the water and so when information technology melts it makes no contribution to ocean level. Its loss over several decades is an of import demonstration that temperatures are increasing in the Arctic.

Has the Sea Level Inverse in the Past?

Sea level has changed naturally in the by, mostly due to the growth and melting of large ice sheets during ice ages [4]. During the peak of the last water ice age (~20,000 years ago), sea level was ~120 m lower than it is today. Because of global warming that occurred between 20,000 and ten,000 years ago (which was natural and not influenced past humans), the rate of body of water level rise was 1.ii cm per year for 10,000 years, until it leveled off to zero. During this span of fourth dimension, several episodes of actress rapid sea level rise happened. For example, about 14,000 years agone, the rate of sea level rise jumped to almost 3 cm per year, because of ice canvass melting. The last time when the climate on earth was similar to today'due south climate was 120,000 years ago, which is in between ice age episodes. Sea level so was at least 6 grand college than it is today, almost certainly because parts of the Greenland and West Antarctic ice sheets were smaller than they are at present [4].

This evidence from the by is startling, because it shows that a large bounding main level change is possible due to global warming, and that the rate of change we run across today could also be much greater.

How is the Ice Changing Today?

Since the early 1990s, satellites accept been able to measure the level of the ocean and the surfaces of the ice sheets [2].

The satellites revealed that the world'south water ice sheets are losing mass in unlike ways. For Greenland, the southern half of the ice sheet is experiencing water ice loss through surface melting due to global warming. In Eastward Antarctica, a few regions at the ice edge are experiencing ice loss because of the warm ocean, but this is not at meaning levels all the same. The largest and most worrisome changes have been measured in West Antarctica. Hither, in the last 20 years, ocean warmth has caused the edges of several glaciers to retreat by tens of kilometers. Some scientists believe that the West Antarctic ice sheet has started to suspension up [5].

Satellite measurements have also allowed us to measure out the sudden disintegration of water ice shelves beyond parts of Antarctica. Several of these have collapsed very apace (within a few days) over the past 20 years, with the immediate effect of increasing the flow of water ice into the bounding main.

Is Global Warming, Acquired by Humans, Responsible for the Ice Sail Changes?

The changes observed in Greenland are almost certainly the result of global warming, with increased air temperatures melting the snow and ice. Thermal expansion of the ocean and melting of small glaciers will likewise occur considering of global warming. The changes observed in Antarctica cannot exist as hands linked to humans, however. The ocean water responsible for Antarctic ice loss probably warmed up several hundred years ago. Nevertheless, the transfer of body of water warmth to the water ice is the outcome of bounding main currents, which may take inverse recently due to changes in atmospheric conditions, such as wind direction. A computer model predicts that ocean currents may modify in an of import region of West Antarctica later this century, because of global warming due to human activities [6]. This change in bounding main currents might lead to large parts of the West Antarctic ice canvas to cook more than now, due to warmer water in contact with the ice.

The rate at which the ice shelves are melting in several regions of Antarctica appears to exist linked to modern global warming. If warming continues, ice shelves on the whole continent may also become vulnerable. This worries scientists because the loss of the largest ice shelves in Antarctica would mean that the West Antarctic ice sail could be exposed to warmer ocean h2o and begin to melt as well.

How Will Sea Level Change in the Future?

Because of the rise in bounding main level that nosotros have seen in the recent past, and because of global warming, scientists are pretty certain that sea level volition keep to ascent over the coming decades, as glaciers and water ice sheets melt and as thermal expansion of ocean water occurs.

In 2013, a report by a grouping chosen the Intergovernmental Panel on Climatic change (IPCC) stated that, under a "concern every bit usual" situation (pregnant that we proceed burning fossils fuels in the hereafter every bit nosotros do today), the world's ice sheets are probable to contribute betwixt 3.5 and 36.8 cm to sea level by 2100. This, added to sea level rise through thermal expansion of the warmer sea water and glacier melting, means that in 2100, sea level may be effectually ane m college than information technology is today.

The charge per unit of sea level ascension is also likely to increase past the end of this century. The IPCC concluded that the "business as usual" scenario will lead to an increase in the charge per unit of change to between 0.7 and one.6 cm per yr by 2100. These values are similar to the rate of sea level rise during the end of the last ice age. Even if nosotros practise reduce our greenhouse gas emissions to zero during the side by side few decades, the minimum sea level rise expected by 2100 will be about xl cm.

How Will Sea Level Rise Affect the Countries of the Earth?

The issue of ice canvass melting on sea level is different across the world [7].

So, when the sea level rises, people will exist affected in different ways, depending on where they alive. The UK is used to occasionally dealing with ascension ocean level for brusk periods of time, specially when at that place are storms at the same time as when the tides higher than usual. If the IPCC predictions are correct, we must consider the possible increase in sea level on pinnacle of natural tidal surges. This will cause dangerously high tides to occur more often in the coming decades, and these time to come tides might be more than subversive than we are used to.

In farming regions most the coast, seawater flooding on land can contaminate the soils with table salt, making them less able to support the growth of crops. The salty h2o may besides get into hole-and-corner stores of fresh water (known every bit groundwater), which is the source of important drinking h2o and besides for farmers to abound crops.

In littoral cities, sea level rise will cause more than flooding to houses, businesses, and while it may seem sensible to consider moving cities away from harmful floods, especially as we know information technology will likely happen in the future, our cities toll and so much to develop that we are more probable to simply effort to protect them from rise sea levels. A vision of our cities about the sea involves them with walls facing the body of water several meters loftier, with the street level of the cities themselves being below the level of the ever rising sea.

Summary

Bounding main level ascent has been measured beyond the world since 1850. The world's oceans are now xx cm higher than they were back so. This is due to global warming acquired by greenhouse gas emissions from the burning of coal, oil, and gas. The change since 1850 is pocket-sized compared to body of water level changes that occurred farther back in fourth dimension, even so. During the ice age 20,000 years ago, sea level was 120 m lower than it is today. This shows us two things (ane) that substantial changes to sea level are possible and (2) when the climate warms, the ice melts and sea level goes up. In the futurity, sea level will go on to rise, possibly by as much as 1 m past the end of this century, if we do not reduce our greenhouse gas emissions. Such modify poses great issues for the 250 meg people who live close to the sea. Information technology will affect our power to grow crops in coastal farms, brand it difficult to maintain the quality of drinking h2o, and volition alter the mode we live in and develop our cities.

Glossary

Global warming: ↑ While climatic change occurred throughout Earth'due south history, the warming observed since 1850 is a outcome of the emission of greenhouse gases to the temper due to the called-for of coal, oil, and gas. The world is more than 1° warmer than it was in 1850, and the sea level is 20 cm higher.

Water ice sheet: ↑ A big ice mass, which flows over hills and valleys and occupies a large portion of a continent. The world has only 3 major ice sheets today (Greenland, West Antarctica, and East Antarctica).

Glacier: ↑ A modest ice mass frequently located within a valley. The world has around 200,000 glaciers.

Ice shelf: ↑ A thick (several hundred meters) region of floating water ice, which receives ice from the water ice canvas, and which loses water ice past icebergs produced at the ice shelf edge and by melting at its underside.

Sea ice: ↑ A very sparse (1–2 m) layer of ice that floats on the sea. Sea ice grows during the cold winter months and melts during the summer months. The amount of summertime sea ice in the Arctic has been reducing in the last few decades; Antarctic sea ice alter has been more variable.

Ice historic period: ↑ xx,000 years ago, the world was several degrees colder than at present. Ice sheets spread over North America, Scandinavia, and South America, among other places. This ice came from the bounding main, and so the level of the ocean was reduced back then—by 120 m—compared to now.

Conflict of Interest Argument

The author declares that the research was conducted in the absence of whatever commercial or financial relationships that could exist construed as a potential disharmonize of interest.

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References

[ane] ↑ Church building, J. A., and White, N. J. 2006. A 20th century acceleration in global sea-level rising. Geophys. Res. Lett. 33:L01602. doi:x.1029/2005GL024826

[2] ↑ Church building, J. A., Clark, P. U., Cazenave, A., Gregory, J. M., Jevrejeva, Southward., Levermann, A., et al. 2013. Chapter thirteen: Sea level alter. In Climatic change 2013: The Concrete Science Basis. Contribution of Working Grouping I to the Fifth Assessment Written report of the Intergovernmental Console on Climate change, eds T. F. Stocker, D. Qin, Chiliad.-M. Plattner, Chiliad. Tignor, Due south. Thou. Allen, and J. Boschung, et al. Cambridge, Britain, New York, NY, USA: Cambridge Academy Press. 1137–216.

[3] ↑ Hay, C. C., Morrow, Eastward., Kopp, R. East., and Mitrovica, J. 10. 2015. Probabilistic reanalysis of twentieth-century bounding main-level ascension. Nature 517:481–four. doi:10.1038/nature14093

[4] ↑ Siegert, One thousand. J. 2001. Water ice Sheets and Late Quaternary Environmental Modify. Chichester, UK: John Wiley. 231.

[five] ↑ Joughin, I., Smith, B. East., and Medley, B. 2014. Marine water ice sheet collapse potentially under way for the Thwaites Glacier basin, West Antarctica. Scientific discipline 344:735–eight. doi:10.1126/science.1249055

[6] ↑ Hellmer, H. H., Kauker, F., Timmermann, R., Determann, J., and Rae, J. 2012. Twenty-first-century warming of a large Antarctic ice-shelf crenel past a redirected littoral current. Nature 485:225–8. doi:10.1038/nature11064

[seven] ↑ The Ice2Sea Consortium. 2013. From Ice to High Seas: Sea-Level Rise and European Coastlines. Cambridge, United Kingdom.

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Source: https://www.frontiersin.org/articles/244113

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