We hear a lot about sea level rise in the context of climate change. But what are the mechanisms by which the water is rising? There are three factors:
To further complicate an already complex matter, these changes in ice volume aren't happening in a vacuum. NASA has this nice visualization [7](I couldn't figure out how to embed it here, but please go review it, it's only 1:08 minutes long) of the snowfall Antarctica experienced over the 20th century. As it turns out, because many parts of Antarctica saw increased snowfall, this helped mitigate the sea level rise we would have otherwise expected (by their estimates, this amounted to about 0.4 inches).
As sea level rises, it pushes inland. How far it penetrates depends on the interplay of several factors.
Along the Mid-Atlantic coastline from about New York City to Cape Hatteras, North Carolina, the combination of climate change-induced sea level rise, a rapidly sinking coastline, coastal currents that reinforce sea level rise, and a very broad, flat coastal shelf results in relative sea level rise that is about twice the global average.
While sea level rise might feel like a more direct threat to some human settlements, increasing ocean temperatures themselves carry important consequences to understand, too. The rising ocean temperature is having dramatic effects in some areas. Along polar coastlines, sea ice is thinning and melting altogether, opening the coastlines for modern human development, but causing traditional societies and wildlife that depend on the presence of sea ice to move or die. Coastal permafrost is melting quickly, causing shoreline collapse and rapid coastal retreat, damaging ecosystems and human structures –– indeed, entire Native Alaskan settlements are moving as the villages literally collapse. In tropical areas, rising ocean temperatures are contributing to coral bleaching and death, destroying these rich ecosystems worldwide and wrecking tourism industries in many locations.
Perhaps an even greater threat associated with climate change is ocean acidification. The global ocean absorbs a major proportion of the atmospheric carbon dioxide emitted by fossil fuel burning and other human activities. The absorption of CO2 is acidifying ocean water. Scientists estimate that since the beginning of the Industrial Revolution, ocean acidity (in terms of H+ ion concentration) has increased 30 percent and will increase much more in the future. The main concern is that increasing acidification could affect major oceanic carbonate-based species and ecosystems–– from plankton, to corals, to shellfish.
All these impacts are happening today and will certainly increase in the future. Sea level rise will continue to accelerate from glacial melt and especially from thermal expansion; it could become catastrophic if the Greenland or West Antarctic ice sheets were to collapse. Ocean storms such as hurricanes are expected to intensify, and some scientists think that ocean storm frequencies could increase in the future. Accelerating sea level rise and more intense storms will mean that storm surge and wave damage will be much greater, as will be coastal erosion. Coastal ecosystems will come under even more stress than they are feeling today. Ever-increasing ocean temperatures and acidification could mean the end of corals, and a worst-case scenario could see the collapse of major ocean food chains.
Sea level responds to two elements of climate change. First, as the lower portions of the atmosphere warm, freezing levels rise and move poleward, causing glaciers to melt in mountain and polar regions. The resulting meltwater drains to the oceans and increases their volume, thereby raising sea level. Scientists have understood the relationship between sea level and glaciers for more than a century: when ice sheets build on the continents, sea level goes down by 100 meters as the water from the oceans goes into these glaciers; when the ice sheets melt, water rushes back to the oceans and sea level rises, pushing coastlines miles inland from their positions during glacial maxima. Human-induced global warming is therefore augmenting this natural process.
Sea level also responds to climate change through the thermal expansion of water. When water heats, it expands; as the ocean heats with global warming, it expands. As long as ocean temperatures continue to increase, the global ocean will continue to expand.
To understand the human risks of climate change in the coastal zone, it is useful to examine the vulnerability of coastal people and places to climate change impacts. Recall that there are three dimensions of vulnerability: exposure, sensitivity, and adaptive capacity. Exposure usually relates to physical vulnerability, whereas sensitivity and adaptive capacity relate to social vulnerability.
As described in the account of physical impacts above, exposure of coastal people and places is increasing. Climate change is exposing billions of people and their built environments to rising sea levels, more intense storms, enhanced storm surge, and worse coastal erosion. These people are exposed to degrading and reduced ecosystems, upon which many people depend for their livelihoods.
How much this increased exposure harms people and places depends on their sensitivity. In underdeveloped and developing countries, hundreds of millions of people residing in the coastal zone live in poverty, and their livelihoods are at risk of harm by climate change. Many of these people are very young or very old, which makes them even more sensitive. In addition, these impoverished people tend to live in substandard housing, without running water or adequate sanitation, nutrition, and health care; burgeoning poverty, corruption, and overcrowding mean that many of these areas are getting worse, rather than better over time. Coastal hazards associated with climate change exacerbate these infrastructural challenges, sometimes greatly.
In developed countries, socioeconomic safety nets are much greater and far fewer people are directly sensitive to the impacts of climate change. Instead, the sensitivities relate to the built environment and can still be great. Inundation from sea level rise and storm surge are the greatest threats. Consider the case of New York City, where trillions of dollars in sophisticated infrastructure -- subways, telecommunications, sewers, and water systems -- exist below ground and could easily be submerged by storm surge in the short run and permanent inundation in the long run. If such flooding occurred, the impacts would cascade around the world. For instance, if workers in the financial district could not get to work because the subways were closed, and if the telecommunications connecting to the New York Stock Exchange were to go down, financial chaos and crisis would spread worldwide. Given that the world’s three major financial centers (New York, London, and Tokyo) are coastal cities, it is clear that in the long term even more affluent countries are sensitive to coastal zone impacts of climate change.
We're sensitive to different things. In sum, it is possible to say that sensitivity to climate change is increasing in the coastal zones of undeveloped, developing, and developed countries. In less affluent countries, sensitivities tend to involve direct impacts on people, but in more wealthy countries, sensitivities are to infrastructure and therefore are felt by individuals and households indirectly. The interconnectedness of the global society means that coastal zone sensitivities and impacts propagate throughout the world. This sensitivity to climate change is mounting in coastal areas because of growing populations and their associated infrastructure.
Adaptive capacity provides the means to decrease vulnerability by either reducing exposure or lessening sensitivity. In the coastal zone, adaptive capacity varies greatly at all scales, from person to person, household to household, neighborhood to neighborhood, settlement to settlement, and country to country. Many factors affect adaptive capacity -- financial resources, technological resources, political resources, and many more. All things being equal, people and places with greater financial resources have greater adaptive capacity. For instance, a rich city might be able to afford to build a sea wall around the city, but a poorer city might not. The rich city is more likely to have a strong intellectual and educational heritage and the technological means to design the sea wall, whereas the poorer city might still possess these characteristics, but it cannot apply them without access to funding. However, even the rich city might not be able to build the sea wall if the political elite are ideologically opposed to doing so; if the poorer city does not follow that ideology and has strong political connections to the nation’s rulers and access to national funds, then they might, in the end, be able to build the sea wall.
The physical impacts of climate change on coastlines are bad, but the human impacts could be even worse. Humans put more pressures on coasts than any other area, which should be no surprise to you now that you've seen how reliant on the coasts are settlements are.
Links
[1] https://www.noaa.gov/education/resource-collections/climate-education-resources/climate-change-impacts
[2] https://climate.nasa.gov/news/2680/new-study-finds-sea-level-rise-accelerating/
[3] https://www.nationalgeographic.com/environment/global-warming/big-thaw/
[4] https://www.nationalgeographic.com/magazine/2017/07/antarctica-sea-level-rise-climate-change/
[5] https://www.nature.com/articles/s41586-018-0179-y
[6] https://www.pnas.org/content/116/4/1095
[7] https://svs.gsfc.nasa.gov/13117
[8] https://www.nature.com/articles/ncomms7346
[9] http://www.flickr.com/photos/usarmyafrica/5157191333/
[10] http://www.flickr.com/photos/usarmyafrica/
[11] http://creativecommons.org/licenses/by/2.0/
[12] https://www.grida.no/resources/7332
[13] https://creativecommons.org/licenses/by-nc-sa/2.0/
[14] http://climate.nasa.gov/evidence/index.cfm
[15] https://www.ipcc.ch/report/ar4/wg1/observations-ocean-climate-change-and-sea-level/
[16] https://www.grida.no/resources/5638
[17] http://onesharedocean.org/public_store/lmes_socioeco/population/lmes_socio_eco_coastal_population_2010_100km.png
[18] https://www.washingtonpost.com/news/wonk/wp/2015/09/03/how-so-many-of-the-worlds-people-live-in-so-little-of-its-space/
[19] http://www.oceansatlas.org/subtopic/en/c/114/
[20] https://www.flickr.com/
[21] http://www.flickr.com/photos/bear_in_va/
[22] http://creativecommons.org/licenses/by-nc-sa/2.0/