Sea Level Rise, Due to Human Activity, Imperils Many

Summary. This post discusses three newspaper articles concerning global warming-induced sea level rise, which all appeared in a one-week period about the third week of April, 2017.

Sea level rise is inexorable, already irreversibly “baked in” to the planet’s climate, because melting of ice in the summer season is not restored by new snow and ice in the winter, and because the melted water flows away into the ocean.

Sea level rise is already causing human societal and economic damage around the world.  It will continue unabated, and likely worsen, in future centuries.  To minimize these harms, the world has to minimize greenhouse gas emissions to near zero as soon as possible.  This process would be significantly advanced by adhering to the Paris climate agreement. 

                                          *         *         *         *         *

From the Washington Post

 

 

The Washington Post reported on April 26, 2017 that the rate of sea level rise now foreseen by scientists is considerably higher than published only four years ago by the Intergovernmental Panel on Climate Change (IPCC) in its Fifth Assessment Report.

The Post article reports that the projections are a collaborative effort among 90 scientists, which was subjected to peer review by 28 other scientists.  Climate models based on two scenarios for continued rates of emission of greenhouse gases to the year 2100 were used for the projections.  One is a moderately stringent policy limiting emission rates.  The second is a scenario based on continued unconstrained emission rates comparable to those that reflect today’s fuel use.  The results are shown in the following table, which also includes the 2013 IPCC projections for comparison.

Scenario	Predicted sea level rise by 2100 [2013 IPCC prediction]
Moderately stringent	At least 52 centimeters (1.7 feet) [32 centimeters (1 foot)]
Unconstrained	At least 74 centimeters (2.4 feet) [45 centimeters (1.5 feet)]

The updated estimates take into account the increased rate of melting of the Greenland Ice Sheet and Antarctic ice shelves recently observed, and expansion of the liquid ocean due to its higher temperature, among other contributing sources.

                                          *         *         *         *         *

From the New York Times

This article reports that Tasmania, the island south of the Australian mainland, is already suffering the ravages of sea level rise.  The shoreline is being eroded by rising seas, and trees are being uprooted and falling into the sea.  An abandoned shoreline coal mine is being filled in by the sea.  The article states “The ocean is rising in large part…because people the world over have burned so much coal, pumping planet-warming carbon dioxide into the air. Perhaps a new stone marker [referencing a seaside prisoners’ graveyard] ought to be planted above the eroding mine: Cause, Meet Effect.”  A Tasmanian ecologist stated, with some irony, “It’s a smoking gun for sea-level rise causing an acceleration of erosion.  And it’s coal! Mined for burning!”

The article summarizes manifestations of worsening global warming: “In country after country, managers of national parks and other historic sites are realizing that climate change, with its coastal flooding and erosion, rising temperatures and more intense rainstorms, represents a profound risk to the heritage they are trying to preserve.”  It mentions damage to the Statue of Liberty’s foundation by Hurricane Sandy, loss of most of the glaciers in America’s Glacier National Park, damage to Australia’s Great Barrier Reef due to rising ocean temperature (vindicating a 10-year old prediction), among many other examples.

                                          *         *         *         *         *

https://www.nytimes.com/2017/04/20/magazine/how-singapore-is-creating-more-land-for-itself.html?_r=0

Singapore is an independent island city-nation just off the coast of the southern tip of Malaysia.  It is a thriving metropolis, whose economic base is commerce and the financial industry.  The article notes that Singapore has felt the limitations of its small land area for decades.  This has constrained the ways it can develop additional useful real estate as its fortunes continue to grow. 

In recent years this quandary has been worsened by the encroachment of rising sea levels.  Singapore fortunately has the financial resources artificially to expand its land area by robbing it from the sea.  The image above shows one example.  The city sinks massive ocean-resistant caissons (seen above from the air) into the sea bed surrounding its natural land base, forming void rectangular enclosures.  It then imports huge quantities of sand, or of pulverized rock, and fills in the rectangles to provide new land area which, when completed, will form new surface area for development.  The new land is high enough to withstand sea level rise in the coming years.

The article contrasts the case of affluent Singapore with other, more impoverished, island “micro-nations” that are losing the battle against rising seas.  Solomon Islands is a Pacific Ocean nation on six major islands and several hundred smaller islands, with an area of 11,000 sq. mi.  The article notes that five small islands have already disappeared under rising seas.  Kiribati has bought 6,000 acres of land 1,000 miles away in Fiji for resettlement of its people.  The Maldives is considering a similar purchase in Australia.  Some of the people living on the island micro-nations of Tuvulu, the Marshall Islands and Nauru have already departed.

Discussion

Newspaper reports on sea level rise.  The examples cited in the articles above pinpoint the flooding, and consequent damages, to be expected along coastlines all over the world as sea levels continue rising.  Man-made global warming, the main cause for the rising seas, is unequivocally due to humanity’s burning of carbon-containing fuels for energy, emitting the greenhouse gas carbon dioxide into the atmosphere.  (Other man-made greenhouse gases also contribute to warming.) 

The fundamental problem is that carbon dioxide remains resident in the atmosphere for centuries because there are no natural processes that remove it at the speed and on the massive scale needed to balance the excess amounts that we produce.  As a result, warming will continue worsening until emissions are effectively minimized to near zero. 

Polar melting.  As noted in the Summary, the long-term average temperature of air in contact with the Greenland ice sheet and of ocean water in contact with the Antarctic ice shelves is already warm enough to lead to net melting of these ice reservoirs, raising global sea levels.  We cannot go back to a planetary regime having a lower temperature (which might slow or stop melting of the ice) because of the permanence of carbon dioxide in the atmosphere.  Consequently the sea level is projected to increase for centuries.  Projected higher temperatures will worsen this trend.

The “social cost of carbon” is an economic term for a framework that attempts to place direct financial costs, as well as indirect societal costs, on the consequences of carbon dioxide-induced global warming.  This is necessary because direct costs for the use of carbon-containing fossil fuels stop at the point of sale of the fuel.  The costs incurred as consequences of the resulting global warming are not reckoned in the sale price. 

This may be contrasted, for example, by the costs that residents bear to have their household waste removed by tax-supported services, or the charges that they pay for treatment of their waste water.  The separate expense of handling the waste is directly borne by property owners and/or municipal taxpayers.  No analogous cost for waste treatment is built into the cost structures of fossil fuel-derived energy use.  This is the accounting that enters into pricing the social cost of carbon.

Contributions to the social cost of carbon are seen in the journal snippets presented here.  Singapore is fortunate in having the resources to protect itself from sea level encroachment.  The other oceanic island micro-nations mentioned here do not; they face existential threats in the near future. 

In the U. S., coastal communities in Miami and south Florida, as well as Norfolk, Virginia, now suffer fair weather flooding at high tide, due to higher sea levels, that had not occurred previously.  Their cost of carbon lies in the extensive, expensive barriers they are forced to put in place to minimize the flooding.  Likewise, the New York region is planning to construct similar barriers as a defense against the possibility that future storm surges similar to that of Hurricane Sandy could occur.  All these projects were not foreseen in earlier budgeting processes.  The additional expenses for them become unexpected taxpayer burdens at the state and local levels.  They clearly represent social costs of carbon that are not included in the prices paid for fossil fuels at the time of use.

Conclusion

Three simultaneously published newspaper articles have pointed out the present and future harms to humanity due to sea level rise.  The rising level is due to humanity’s burning of fossil fuels, worsening the carbon dioxide-induced greenhouse effect and producing warmer global average temperatures that melt polar ice caps.

We must work together to minimize future increases in the carbon dioxide burden of the atmosphere in order to slow continued sea level rise.  (The world’s temperature is already too high to stop it outright.)  The Paris climate agreement of 2015 is a good start on this path.  All nations of the world should embrace its provisions, and improve the emission limits it has created.  Rejecting the agreement would be at humanity’s peril.

© 2017 Henry Auer 

How Sea Level Rises: A Tutorial

Summary.  Among the documented effects of global warming has been a rise of the average sea level around the globe since 1900.  This post explains, in tutorial fashion, how this happens.

First, the water in the oceans expands in volume as its temperature increases.  Expansion is constrained to occur only in the upward direction, leading to sea level rise.  Second, land-based glaciers and ice sheets melt from their upper surfaces as the air they contact warms above the melting point of water.  Third, ice shelves buoyed by the ocean in Antarctica melt from their lower surfaces as the ocean circulating under them warms.  All these processes contribute to observed sea level rise.  Both melting processes are expected to continue indefinitely as long as warming produces temperatures in the air and in the underlying ocean that remain above the melting point.

 

Introduction.  One of the consequences of global warming identified by climate scientists is sea level rise.  Higher levels of the oceans’ waters potentially affect shorelines and low-lying islands all around the world.

The United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC), in its Fifth Assessment Report (5AR), includes the following graphic showing the extent to which the global average sea level has risen in past decades up to the present.

Global average sea level change from 1900 to the present.  Each color presents a different data set.  The red line gives satellite measurements beginning in 1993.  Shadings, when present, characterize statistical variability in the data. mm, millimeters.

Source: IPCC 5AR Working Group I; http://www.climatechange2013.org/images/report/WG1AR5_SPM_FINAL.pdf.

 

The graphic shows that since 1900 global average sea level has risen by about 200 millimeters (about 7.9 in.).  It is expected to continue rising indefinitely into the future (see below).

This post describes two main factors contributing to rising sea level, expansion due to heating and melting.

Expansion of water upon heating.  Like all forms of matter, water expands when it is heated and contracts when it is cooled.  At a temperature of 20ºC (68ºF) water expands by a factor of about 0.00020 per ºC (0.00011 per ºF).  We may think that the expansion occurs in all directions, as if the water of the ocean were in an elastic balloon.  This would have the effect of minimizing expansion in the vertical direction.  But in fact, the waters of the oceans are constrained on the bottom by the ocean floor and on the sides by shorelines, so that all the expansion occurs only upwards. 

Oceanographers have been measuring temperature changes in the ocean by depth, and find that the ocean temperature has increased in the last several decades down to depths of several hundred meters (see below).  For the sake of this discussion, if the temperature increased on average from 20ºC to 21ºC down to a depth of 700 meters (2,275 feet; defined as the “upper ocean”) expansion would cause the surface of the water to rise by 140 mm, or 5.6 in.  This simple calculation shows that an increase in surface temperature of the ocean is a contributing factor for sea level rise.

Melting of land-based ice.  Some sea ice arises by freezing of the ocean water.  This process transfers some water from liquid to solid, say as the polar winter arrives, which then melts back to the liquid during the polar summer.  Such cyclical changes in state have no net effect on sea level.

Transfer of land-based ice to the oceans, however, a one-time process, represents a net addition of water to the sea, raising its level.  The new water was not part of the ocean system before melting.   There are several sources of new ocean water.  Mountain glaciers at high elevations are melting around the world as a result of global warming.  The water courses through streams and rivers, and ultimately reaches the sea. 

Ice sheets over land masses, such as the Greenland ice sheet, melt from their upper surfaces when the air is above the freezing point.  This water penetrates gaps in the ice sheets and finds its way to the ocean.  Additionally, land mass glaciers at the interface with the sea calve icebergs as the glacier flows downhill toward the sea.  The solid ice in the icebergs and the water that it gives rise to as it melts contribute to raising the sea level.

This process can be diagrammed using the following simplified graphic:

Ice cube model for melting glaciers and ice sheets.  The ice cube melts at exactly 0ºC.  Ice cube image from www.dreamstime.com.

 

At the left in the diagram, the air temperature is below the melting point of the ice cube, so it stays solid and does not lose any mass.  The second frame shows the case for the air temperature being exactly 0ºC.  Under these conditions solid ice and liquid water, shown as the tiny white puddle at the base of the ice cube, are in equilibrium with each other.  Again the ice cube essentially remains unchanged, losing no mass. 

In the third frame the air temperature is 1ºC (33.8ºF).  Ice melts because heat contained in the air is transferred to the solid ice, providing the energy needed to melt it (see here  for further explanation of this notion).  The ice cube melts relatively slowly at this moderate air temperature, creating the small water puddle around its base and making the ice cube slightly smaller.  The ice cube will continue to melt slowly as long as the air temperature stays about 1ºC.

The fourth frame shows the case in which the air temperature is 2ºC (35.6ºF).  The ice cube melts more rapidly, because the rate of heat transfer from the air to the ice is higher.  Now the water puddle is quite large, and the ice cube has shrunk considerably in size.  The ice cube will continue to melt rapidly as long as the air temperature remains about 2ºC. 

The ice cube model can be taken to represent the melting of high-altitude mountain glaciers, land-mass ice sheets such as the Greenland ice sheet, and, indirectly, the calving of icebergs from glaciers moving into the sea; the latter movement is accelerated by global warming.  In addition some glaciers that were earlier in contact with the ocean have melted so fast that their leading edges have receded from the ocean and are now found at some considerable distances from the shoreline.

Melting of Antarctic Ice Shelves.  Ice shelves, such as are found in Antarctica, are large areas of ice that are the oceanic ends of land-based ice sheets that flow over the ocean and float on its surface.  Ice shelves are distinguished from ice sheets by the fact that they cover ocean water, rather than land.  An ice shelf is diagrammed in the graphic below:

 

                            Simplified model of an ice shelf extending over the ocean.

 

An ice shelf does not primarily melt from the upper surface.  The Antarctic region is sufficiently cold that surface melting does not occur to a significant extent.  Rather the ice shelf melts from below, by contacting the liquid ocean, whenever the water temperature is above the equilibrium melting temperature of the ocean, about -2°C (28.4°F; this lower melting point is due to the dissolved salts present in ocean water).

Melting of the ice shelf eats away at its substance from its lower surface, as shown in the following graphic:

 

Mechanism of melting of an Antarctic ice shelf from its lower surface.  Warm ocean water flows toward the shore over the ocean floor (orange arrows).  It transfers its heat to the undersurface of the ice shelf, melting it.  The water containing the melted ice remains near the upper surface because, having a lower salt content, it is less dense than the ocean water flowing in.  This newly-melted water flows back toward the bulk ocean (orange arrows).

 

The result of this melting process is to add water substance to the ocean that was not present before, raising the level of the ocean.  In addition, the ice shelf thins and recedes as melting proceeds, including breaking off of ice floes that will continue to melt.  The rate of melting gets greater as the ocean temperature becomes increasingly warmer than the melting point of ocean water. 

Ocean warming is in fact happening.  5AR estimates  that 90% of the excess heat arising from global warming is stored in the oceans.  The historical trend of the total amount of heat contained in the oceans has been rising from 1950 (the time when these measurements began) to 2010, as shown in the graphic below:

Change in the global mean upper ocean (0–700 m) heat content in joules (a unit of energy) from 1950 to 2010.  The data in different colors come from different data sets, and the shadings in the same colors represent estimates of statistical variability for the given data set.  The values along the vertical axis show the changes from a zero point assigned relative to the mean of all datasets for 1971, and have been computationally adjusted to overlap for the period 2006-2010.

Source: IPCC 5AR Working Group I; http://www.climatechange2013.org/images/report/WG1AR5_SPM_FINAL.pdf.  

 

As the heat content increases the ice shelf will melt more rapidly and more extensively.  Climate scientists expect the global ocean heat content to continue increasing, so that ice shelf melting will continue indefinitely.  As noted above, ice shelf melting can only stop if the ocean temperature remains at or below the ocean melting point for ice. 

 

Conclusion

 

There are two processes contributing to rising sea levels due to global warming, expansion of the volume of water contained in the oceans and net melting of ice mass to become liquid water.

 

Thermal expansion is a natural property of water and other liquids.  As water warms it occupies more volume.  This expansion probably occurs for several hundred meters of depth, raising the level of the surface of the ocean. 

 

Melting of glaciers and land-based ice sheets occurs primarily from their upper surfaces, as heat is transferred from the air to the ice solid, liquefying it.  Antarctic ice shelves, on the other hand, melt from below due to contact with ocean water whose temperature is above the ocean’s freezing point.  In both cases, the rate of melting increases as the temperature of the air, or the liquid ocean, respectively, becomes warmer.  Melting increases the total volume of the earth’s oceans, leading to a rise in the global average sea level.

 

Thermal expansion will cease if and when the global average temperature stops increasing, reaching a new, higher plateau value.  Enhanced melting of ice mass will continue indefinitely, however, as long as the global average temperature remains above the freezing point of ice or of ocean water.  Unfortunately, since carbon dioxide, the principal greenhouse gas, remains in the atmosphere for several centuries, even achieving near-zero annual rates of emission will only stabilize the global average temperature at some new, higher value; with current technology carbon dioxide cannot be removed from the atmosphere.  This means the average temperature of the atmosphere and of the oceans will not fall, and will likely continue to rise.  For this reason land-based ice sheets and Antarctic ice shelves will continue melting indefinitely for generations to come.  The effects on ocean shorelines around the world will be considerable and essentially permanent.

 

 

© 2014 Henry Auer

 

Storm Surges and Sea Level Rise

Summary.  Hurricane Sandy inflicted heavy damage on the northeastern U. S. states of New Jersey, New York and Connecticut on October 29, 2012.  Much of the damage arose from the storm surge of unprecedented intensity that accompanied the storm.

This post summarizes several recent scientific articles characterizing melting of polar ice, historical sea level rise over recent decades, and model calculations projecting future sea level rise.  Melting of polar ice, higher sea levels, and stronger storm surges have occurred in recent years, in conjunction with the long-term increase in global average temperature.  Model projections incorporating various scenarios that continue to emit carbon dioxide predict that sea levels will continue rising to high levels for the next 290 years.

The nations of the world will continue paying the damages caused by extreme events such as Hurricane Sandy, with expenses passed on as higher tax rates and higher insurance premiums, among others.  As an alternative to spending resources on such remediation, humanity should undertake investment in technologies that limit greenhouse gas emissions, and indeed should deploy industrial scale technologies that deplete carbon dioxide already emitted from the atmosphere.

 

Introduction.  Hurricane Sandy struck the state of New Jersey and the New York metropolitan area on Monday October 29, 2012.  It caused damage estimated at upwards of US$50 billion, much of it due to storm surges that impacted wide stretches of shoreline in New Jersey, the heart of New York City, and eastward along the states of New York and Connecticut. 

The ravages of the storm are likely due to factors related to global warming, such as increases in the moisture content of air over warm ocean waters, rising sea levels, and a blocking high pressure system that forced the path of the storm westward toward land instead of northeastward following the coastline.

U. S. President Obama is submitting a request for about US$50 billion to the Congress for emergency funding to help recovery efforts from the storm.  This amount is based on estimates of the physical damage suffered from the storm and costs for new infrastructure to minimize future storm threats.  It is less than the amount of US$80 billion sought by the affected states, New Jersey, New York and Connecticut, which includes estimates for complete restoration of property and lost economic activity.

Much of the damage from Hurricane Sandy arose from an ocean storm surge.  This was made worse by the documented increase in sea levels in recent decades attributed to global warming.  The world-wide average sea level rise is shown in the graphic below.

 

Global average sea level trend from 1870 to 2000, referenced to a zero value given as the average for the period from 1961 to 1990, in mm (50 mm is approximately 2.0 in.).

Source: Intergovernmental Panel on Climate Change, 4th Assessment Report, 2007; http://www.ipcc.ch/publications_and_data/ar4/syr/en/figure-spm-1.html. 

 

Sea level rise has not attracted as much of the public’s attention as have other phenomena related to global warming, such as extreme weather events more generally.  Purely by coincidence several articles in scientific journals appeared in recent weeks related to sea level rise.  This post reviews some of them.  They were all submitted by their authors to the respective journals some months before Hurricane Sandy hit, so they cannot be considered to have been stimulated by this event. 

 

Historical Record of Sea Level Rise

Polar Ice Melting.  A team of 47 climate scientists from 26 institutions in eight countries, assembled as the Ice Sheet Mass Balance Exercise, reviewed and collated existing data on loss of ice mass in Greenland and Antarctica. 

 

Details: Their report (A. Shepherd and coworkers, Science, Vol. 338, pp. 1183-1189, 2012 ) assessed previous data sets obtained over 19 years by satellite using the methods of radar altimetry (elevation measurement), laser altimetry, radar interferometry between two satellites and gravimetry (measuring changes in the force of gravity due to lost ice mass), 32 years of model calculations of surface mass balance, and other models of changes in glacier properties.  There was a need for this because the earlier reports from one technique or another were never considered together.  It was not clear whether the results were or were not consistent.

 

After demonstrating that the differing methods produced consistent results, Shepherd and coworkers obtained results for Greenland as a whole, and for three different regions in Antarctica, as summarized in the following table:

 

 

Source: Shepherd and coworkers, Science, Vol. 338, pp. 1183-1189, 2012; http://www.sciencemag.org/content/338/6111/1183.full.

 

About two-thirds of the change originates in Greenland and West Antarctica.  The rates of mass loss become more pronounced at the end of this time span.  This can be seen in the following graphic:

Cumulative traces of ice mass (left vertical axis) and the equivalent contribution to sea level rise in mm (right vertical axis; 5 mm is about 0.2 in.).

Source: Shepherd and coworkers, Science, Vol. 338, pp. 1183-1189, 2012; http://www.sciencemag.org/content/338/6111/1183.full. 

 

The significance of the report by Shepherd and coworkers is emphasized in an accompanying news comment (R. A. Kerr, Science, Vol. 338, p. 1138, 2012),  as providing a single set of results that all agreed to.  The report firmly establishes the large and accelerating rate of loss of ice mass especially from Greenland and West Antarctica.  Kerr points out that the loss reported represents about 20% of the contribution to sea level rise, the remainder originating from melting mountain glaciers and the expansion of the water of the oceans as its temperature increases.  All these effects are due to global warming.

 

Mechanisms of Polar Ice Melting.  In a review I. Joughin and coworkers (Science, Vol. 338, pp. 1172-1176, 2012) discuss the present state of understanding of the factors involved in ice sheet loss in Greenland and Antarctica. 

 

 

Details:  The principal source of melting is the heat content of ocean waters bathing the ice shelf (Antarctica) or the outlet glacier (Greenland).  The mechanisms involved are complex, and differ in the two cases.  The Antarctic ice shelf floats extensively over ocean waters, which circulate according to circumpolar ocean currents, with changes in density arising as fresh water from melted ice enters the ocean, and from tidal mixing at the surface interface with the ice.  Recent warming of the underlying ocean currents leads to more rapid melting of the ice shelf from its lower surface.

 

 

Greenland glaciers, on the other hand, migrate directly over land surfaces without floating on the ocean, so the flow of currents differs greatly.  These glaciers calve icebergs, and are bathed in the North Atlantic Circulation.  Surface melting occurs in Greenland, but not in Antarctica, and the liquid descends through glacial crevices to the ice-land interface, thus changing the salinity of the ocean at the glacial front. 

 

 

Over the past two decades, Greenland glaciers have flowed 50% faster than before, likely owing to the effect of global warming on providing warmer water at the ice-ocean boundary.  The authors conclude that much still remains to learn about these phenomena.  Incorporating the present knowledge into general circulation models in order to predict future melting rates will be successful if the models operate with high spatial resolution.  It appears that such models for melting “indicate the potential for far more extreme changes within this century than had been anticipated”.

 

Atlantic storm surges.  A. Grinsted and coworkers (Proceedings of the (U. S.) National Academy of Sciences, Vol. 109, pp. 19601-19605, 2012), based in China, Sweden, Finland and the United Kingdom, studied storm surges along the Gulf of Mexico and the U. S. Atlantic coast over the period 1923 to 2008 by analyzing tide gauge readings from six locations along these shorelines.  (1923 was chosen for the start because it is the year of a strong storm surge; active surges continued during the 1930’s.) 

 

 

Details:  The small number of locations is justified because surges extend large distances from storm centers (their cutoff was 250 km (155 mi,)) and last several days.  The authors constructed a new surge index which accounts for the potential energy contained in elevated water levels, and adjusts the data by removing an annual background tidal level for each location.  The results are correlated with whether an event falls in a cold year or a warm year, where deviations from the median temperature for the interval studied here govern whether an event is classified as a cold or warm year event.  The temperature data are global average annual temperatures.  They cross from being generally cold to being strikingly warm at about 1978; the years in the period from 2000 on are generally 0.4-0.7ºC (0.7-1.3ºF) above the median.  This temperature trend is already quite well known.  The authors then generate a graph of the surge index for all surge events, plotted against the frequency of their occurrences.

 

 

Surge events were segregated according to whether they occurred in a cold year or a warm year.  Strikingly, events with high surge indexes (i.e., having the highest energy at landfall) occur twice as frequently in warm years as in cold years.  Additionally the authors find that warm years generate more storm surge events than do cold years. 

 

This suggests that global warming leads to more intense storm surges, understandably since warmer air can hold higher amounts of water vapor, leading to stronger winds.  Wind strength is an important factor in creating the energy contained in a storm surge.

 

In a commentary on the work of Grinsted and coworkers, G. J. Holland (Proceedings of the (U.S.) National Academy of Sciences, Vol. 109, pp. 19513–19514, 2012) notes that an advantage of the surge index created by these workers is its inherent assessment of storm intensity, and propensity for damage at landfall, incorporating separate factors such as storm speed, wind speed and overall size.

 

Historical Sea Level Trends.  A. Sallenger and coworkers (Nature Climate Change, Vol. 2, pp. 884–888, 2012) report a hotspot in recent sea level rise along the northeast coast of the U. S. between Cape Hatteras, North Carolina, and Boston, a distance of about 1000 km (620 mi.).  This includes the New Jersey-New York-Connecticut shoreline subjected to the storm surge of Hurricane Sandy. 

 

This study analyzed tide gauge data from 1894 to the present.  Most analysis focused on time windows of 60 years, 50 years and 40 years all ending in 2009.  They find that as the time window narrows and becomes weighted more to recent decades, this hotspot becomes more intense.  The 60 year window shows tide gauges in this region with annual rates of sea level rise in the range (this writer interpreted color-coded data points) of about 1 to 3 mm per year, whereas the 40 year window shows that this rate has increased to 3 to 5 mm per year in most cases.  In contrast to this hotspot, the gauge data from further south than Cape Hatteras and further north than Boston show mostly no sea level rise, indicating that the regional nature of the hotspot appears to be real.  The authors relate that their demonstration of a sea level rise hotspot along the northeast coast is consistent with several model predictions by other workers of such a hotspot.

 

S. Rahmstorf, one of the coworkers with M. Schaeffer in work described in detail below, warned on Nov. 28, 2012 that sea levels have been increasing in recent decades even faster than predicted earlier by the Intergovernmental Panel on Climate Change. 

 

Large Future Sea Level Rise Due to Further Planetary Warming.  M. Schaeffer and coworkers (Nature Climate Change, Vol. 2, pp. 867–870, 2012) modeled sea level rise projected into the future based on a range of greenhouse gas/temperature rise scenarios. 

 

 

Details:  At the United Nations Framework Convention on Climate Change annual conference held in Cancun, Mexico in December 2010 the nations of the world pledged to restrain further emissions of greenhouse gases (GHGs) such that the long-term global average temperature increase would not be greater than 2ºC (3.6ºF) above the level that prevailed before the industrial revolution began.  This limit corresponds to an atmospheric concentration for carbon dioxide or its equivalent GHGs of about 450 ppm (parts per million).  Sea level rise model projections were calibrated by correctly reproducing sea level data starting from the year 1000 up to 2006.  Projections overlapped by starting as early as 1860, extending to the year 2300.

 

 

Large sea level rises are foreseen for 2100, continuing to even higher sea levels by 2300.  In the year 2100, an emissions scenario that maintains the 2ºC limit is predicted to generate a sea level rise of 75-80 cm (29.5-31.5 in.) above the level of 2000, while a scenario with no abatement of emissions generates a rise of about 1 m (39.4 in.) and a radical scenario in which all emissions cease after 2016 provides a rise of about 60 cm (23.6 in.) by 2100. 

 

The oceans contain a great deal of thermal and climate inertia since the ability of liquid water to store and release heat is about 1000 times greater than for air, and various ocean depths circulate to exchange heat content only over very long time frames.  For these reasons sea level rise trends that are apparent in projections at the year 2100 continue along similar trajectories further into the future.  Schaeffer and coworkers extended their projections to the year 2300.  The scenario maintaining the 2ºC limit is projected to generate a sea level rise of 2.7 m (8.9 ft.) above the level of 2000.  A relatively unconstrained scenario (similar to no abatement) is predicted to produce a further sea level rise of about 3.5 m (11.5 ft.).  Even in the third scenario, reducing emissions to zero in 2016, sea level is projected to continue rising to 1.25 m (4.1 ft.) by 2300.

 

Schaeffer and coworkers show by their sea level projections that drastic extents of sea level rise are locked in place already at this time, regardless of which emissions policy is undertaken; only the degree of rise is subject to vary.  They conclude that sea level rise can be constrained “within a few centuries” only by implementing worldwide industrial scale processes to lower the concentration of atmospheric carbon dioxide.  This has not been commonly discussed to date; Schaeffer and coworkers suggest such reductions, for example, by combining a switch to bioenergy (which permits approaching zero net emissions) coupled with use of technology for carbon dioxide capture and geological storage in energy generating facilities.  This combination would result in a cumulative negative flux of carbon dioxide, lowering its concentration in the atmosphere.

Schaeffer and coworkers importantly conclude “A key aspect of [slowing sea level rise] … is the long response time of sea level that is physically expected from the slow response of large ice sheets and the deep ocean to climate change, [which is] also found in [the geologic climate record]. This … means that about half of the twenty-first century [sea level rise] is already committed from past emissions. It further means that mitigation measures, even [radical reductions], have practically no effect on sea level over the coming 50 years and only a moderate effect on sea level by 2100.  [Such measures, however, can have] … a major effect on magnitude of [sea level rise] in the centuries thereafter.”

 

Analysis

 

This post summarizes several recent scientific articles, most of which (except for the Rahmstorf release) were transmitted to the respective journals several months before Hurricane Sandy impacted the northeast U. S. coast.  Thus their publication is not a response to that event.  Shepherd and coworkers, and the comment by Kerr, documented the regions in Greenland and Antarctica that have undergone the most loss of ice mass, generating liquid water that contributes to sea level rise.  Joughin and coworkers review physical mechanisms that come into play in providing the heat that results in melting of ice mass.  Grinsted and coworkers, and the comment by Holland, traced historical tide gauge data, showing that storm surge frequency and intensity have been increasing in recent years and preferentially arise in years of warm global average temperatures.  Sallenger and coworkers analyzed tide gauge data along the northeast Atlantic coast of the U. S. and showed a recent trend of increased sea level rise, and rate of rise, as a hotspot in this region, which is not present along adjacent coastlines.

 

Schaeffer and coworkers, projecting sea level rise trends into the future using several different scenarios for the emission of heat-trapping greenhouse gases, predict that pronounced increases in sea level will occur by 2100.  Furthermore, the trends creating them will continue beyond that time, generating even stronger sea level increases by 2300.  They conclude that worldwide efforts must be undertaken not only to slow the rate of new emissions, but in fact to use combinations of technologies that result in a net depletion of greenhouse gases from the atmosphere.

 

Hurricane Sandy struck the northeastern U. S. in October 2012, causing profound damage, much of it due to Sandy’s ocean storm surge.  This post summarizes that sea levels are rising, and storm surges are becoming more intense, in correlation with increased global warming. 

 

President Obama’s US$50 billion request for unbudgeted emergency relief to help restore the northeast is particularly difficult to consider now, in December 2012, coming as it does during intense fiscal negotiations seeking to balance reducing outlays and increasing revenues.  It is believed the request will not include compensating offsets to spending elsewhere.  This means that any emergency aid passed into law is added to the U. S. national debt, requiring that it be paid back at some later time by increasing taxes and/or cutting spending.  Likewise, insurance companies have been hit hard by anticipated claims arising from the storm.  Their benefit payments will have to be made up by increasing future premiums for weather-related claims.  More generally, because of the high probability that global warming contributes to the damage caused by storms such as Hurricane Sandy, it is expected that future extreme weather events caused or worsened by global warming will inflict continued large financial consequences on the nations of the world for their remediation.

 

In recognition of this clear understanding, Schaeffer and coworkers have called for large scale remediation involving the deployment of new technologies for decarbonizing energy production, including the implementation of carbon capture and storage.  This blog has taken a comparable position many times over the past year or more.  The consideration of the harms brought about by intensifying sea level rise, summarized in this post, creates a clarion call for robust action by all nations of the world to act as soon as possible.  Investment in mitigating technologies will reduce the need for emergency government expenditures as responses to extreme climate events.

 

© 2012 Henry Auer