Oceans Rising ##BEST##

In the natural world, rising sea level creates stress on coastal ecosystems that provide recreation, protection from storms, and habitat for fish and wildlife, including commercially valuable fisheries. As seas rise, saltwater is also contaminating freshwater aquifers, many of which sustain municipal and agricultural water supplies and natural ecosystems.

Oceans Rising

Already, flooding in low-lying coastal areas is forcing people to migrate to higher ground, and millions more are vulnerable from flood risk and other climate change effects. The prospect of higher coastal water levels threatens basic services such as Internet access, since much of the underlying communications infrastructure lies in the path of rising seas.

Of course, communities vulnerable to rising seas can only go so far in holding back the tide. In the Marshall Islands, where rising sea levels are forcing a choice between relocating or building up the land, residents will need help from other nations if they decide to undertake the expensive latter option.

Most predictions say the warming of the planet will continue and is likely to accelerate, causing the oceans to keep rising. This means hundreds of coastal cities face flooding. But forecasting how much and how soon seas will rise remains an area of ongoing research.

The rising seas pose both a direct risk of flooding unprotected areas and indirect threats of higher storm surges, king tides, and tsunamis. They are also associated with the detrimental second-order effects such as the loss of coastal ecosystems like mangroves, losses in crop production due to freshwater salinization of groundwater and irrigation water or the disruption of sea trade due to damaged ports.[6][7][8] Globally, just the projected sea level rise by 2050 will expose places currently inhabited by tens of millions of people to annual flooding and this can increase to hundreds of millions in the latter decades of the century if greenhouse gas emissions are not reduced drastically.[9] While modest increases in sea level are likely to be offset when cities adapt by constructing sea walls or through relocating people,[10] many coastal areas have large population growth, which results in more people at risk from sea level rise. Later in the century, millions of people will be affected in cities such as Miami, Rio de Janeiro, Osaka and Shanghai under the warming of 3 C (5.4 F), which is close to the current trajectory.[8][11]

Societies can adapt to sea level rise in three different ways: implement managed retreat, accommodate coastal change, or protect against sea level rise through hard-construction practices like seawalls or soft approaches such as dune rehabilitation and beach nourishment. Sometimes these adaptation strategies go hand in hand, but at other times choices have to be made among different strategies.[19] For instance, a managed retreat strategy is difficult if the population in the area is quickly increasing: this is a particularly acute problem for Africa, where the population of low-lying coastal areas is projected to increase by around 100 million people within the next 40 years.[20] Poorer nations may also struggle to implement the same approaches to adapt to sea level rise as richer states, and sea level rise at some locations may be compounded by other environmental issues, such as subsidence in so-called sinking cities.[21] Coastal ecosystems typically adapt to rising sea levels by moving inland; however, they might not always be able to do so, due to natural or artificial barriers.[22]

Sea level rise is not uniform around the globe. Some land masses are moving up or down as a consequence of subsidence (land sinking or settling) or post-glacial rebound (land rising due to the loss of the weight of ice after melting), so that local relative sea level rise may be higher or lower than the global average. Furthermore, gravitational effects of changing ice masses and spatially varying patterns of warming lead to differences in the distribution of sea water around the globe.[24][25]

There are broadly two ways of modelling sea level rise and making future projections. In one approach, scientists use process-based modelling, where all relevant and well-understood physical processes are included in a global physical model. An ice-sheet model is used to calculate the contributions of ice sheets and a general circulation model is used to compute the rising sea temperature and its expansion. A disadvantage of this method is that not all relevant processes might be understood to a sufficient level, but it can predict non-linearities and long delays in the response which studies of the recent past will miss.