Global Average Sea Level Research Articles

Towards a global regionally varying allowance for sea-level rise

Allowances have been developed for future rise of relative sea-level (i.e. sea level relative to the land) based on the projections of regional sea-level rise, its uncertainty, and the statistics of tides and storm surges (storm tides). An ‘allowance’ is, in this case, the vertical distance that an asset needs to be raised under a rising sea level, so that the present likelihood of flooding does not increase. This continues the work of Hunter (2012), which presented allowances based on global-average sea level and local storm tides. The inclusion of regional variations of sea-level rise (and its uncertainty) significantly increases the global spread of allowances. For the period 1990–2100 and the A1FI emission scenario (which the world is broadly following at present), these range from negative allowances caused by land uplift (in the northern regions of North America and Europe) to the upper 5-percentile which is greater than about 1m (e.g. on the eastern coastline of North America).

Vulnerability of the Nile Delta coastal areas to inundation by sea level rise

Sea level changes are typically caused by several natural phenomena, including ocean thermal expansion, glacial melt from Greenland and Antarctica. Global average sea level is expected to rise, through the twenty-first century, according to the IPCC projections by between 0.18 and 0.59cm. Such a rise in sea level will significantly impact coastal area of the Nile Delta, consisting generally of lowland and is densely populated areas and accommodates significant proportion of Egypt's economic activities and built-up areas. The Nile Delta has been examined in several previous studies, which worked under various hypothetical sea level rise (SLR) scenarios and provided different estimates of areas susceptible to inundation due to SLR. The paper intends, in this respect, to identify areas, as well as land use/land cover, susceptible to inundation by SLR based upon most recent scenarios of SLR, by the year 2100 using GIS. The results indicate that about 22.49, 42.18, and 49.22% of the total area of coastal governorates of the Nile Delta would be susceptible to inundation under different scenarios of SLR. Also, it was found that 15.56% of the total areas of the Nile Delta that would be vulnerable to inundation due to land subsidence only, even in the absence of any rise in sea level. Moreover, it was found that a considerable proportion of these areas (ranging between 32.32 and 53.66%) are currently either wetland or undeveloped areas. Furthermore, natural and/or man-made structures, such as the banks of the International Coastal Highway, were found to provide unintended protection to some of these areas. This suggests that the inundation impact of SLR on the Nile Delta is less than previously reported.

Sea Level Change and Vertical Motion from Satellite Altimetry, Tide Gauges and GPS in the Indonesian Region

We investigate the sea level rise in Indonesia during the period 1993–2011 using satellite altimetry and tide gauge data. Satellite altimetry indicates a positive sea level rise with mean of 4 mm/yr, which is higher than the global averaged mean sea level rise. At four tide-gauge stations the difference of the sea level trends from tide gauge and co-located satellite altimetry is greater than 3 mm/yr. Land subsidence is found in Jakarta, Surabaya and Benoa. At Enggano and Tanjung Lesung the vertical rates correspond with GPS-derived rates between 2007 and 2009, indicating land subsidence at the first station.

The Science of Global Warming

Global warming is unequivocal, as is manifested in three internationally known global temperature records with the global average temperature rising at a rate of 0.70–0.75◦C per 100 years during 1910–2009 [Wen et al., 2011]. In other words, the earth has warmed more than 0.8◦C since the Industrial Revolution. If it is true that 2◦C above pre-industrial level is a threshold of climate “safety”, we will have to confront a serious situation where less than 1.2◦C warming is permissible in the future [Liu et al., 2011]. According to climate system concept [Wang, 2011], the global warming is not only reflected in global temperature change but also in changes of other climate system components, such as widespread melting of snow and ice, rising of global average sea level, and permafrost degradation [IPCC, 2007]. Due to its great influences and potential risks on the society, global warming now attains more and more concerns from governments, scientists and public media. Today, global warming becomes one of the most important issues, which must be taken into consideration in strategic decision making of national development. As a scientific issue, however, global warming has been studied for almost 200 years [Mitchell, 2002; Cullen, 2011]. And it now has evolved as an independent discipline closely associated with meteorology, oceanography and environmental sciences. In order to review the development of global warming concisely, in this paper, we shall only focus on the science of global warming itself, excluding impacts, adaptation and policy associated with global warming. In 2011, Archer and Pierrehumbert [2011] compiled the previous studies on the global warming and added their brief comments. This work offered a great foundation for further investigating global warming. In order to understand global warming systematically and comprehensively, we summarize ten essential issues based on the five cornerstone literatures from Archer’s compilation together with four IPCC Assessment Reports and the First World Climate Conference. These ten issues will be reviewed as follows. Greenhouse effect Joseph Fourier was the first scientist argued for the greenhouse effect in 1824 [Archer and Pierrehumbert, 2011]. The earth receives energy from the sun and re-radiates to outer space. Calculations based on the planetary energy balance indicate that the temperature of the earth is much lower than 0◦C as opposed to the observation of 14◦C. This discrepancy is believed to be produced by the atmosphere, which traps more long-wave radiation from earth surface and keeps the earth warmer. A mechanism named greenhouse effect is proposed to describe this process. Greenhouse gases An Irish scientist Tyndall in 1849 verified through his designed experiments that CO2 has greenhouse effect on earth’s climate [Tyndall, 1861]. He was the first to correctly measure the relative infrared absorptive powers of the gases including

Managing the Risks of Extreme Events and Disasters

The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), which was completed in 2007 stated that: “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.” It also stated that observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly in increases in temperature. Significantly, the AR4 found that since the mid-twentieth century most of the observed increase in global average temperatures is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. When the term “very likely” is used in this context, it denotes a probability level of 90 per cent or higher.

Groundwater depletion's contribution to sea level rise increasing

Since the turn of the twentieth century, industrial‐scale redistribution of water from landlocked aquifers to the ocean has driven up the global average sea level by more than 12 centimeters. Between 1900 and 2008, roughly 4500 cubic kilometers of water was drawn from the ground, largely to feed an agricultural system increasingly reliant on irrigation. Of that 4500‐cubic‐kilometer total (nearly the volume of Lake Michigan), 1100 cubic kilometers were pumped out between 2000 and 2008 alone. This early‐21st‐century groundwater depletion was responsible for raising global sea level at a rate of 0.4 millimeter per year, an eighth of the observed total. These updated values, falling near the middle of the range of previous estimates, are the product of an investigation by Konikow that drew together a variety of volumetric measurements of groundwater storage.

The global average rise in sea level and the rises of the Northern and Southern Hemisphere average sea levels in the present epoch

The mechanisms for the increase in the global average sea level in the present epoch are studied. The phenomenon of contrasting secular Southern and Northern Hemisphere average sea-level changes is explained; this phenomenon was predicted earlier by the author on the basis of the observed secular northward trend of the Earth’s center of mass at a rate of 5–6 mm/yr. Studies of sea-level changes using altimetry method are criticized.

Sea-Level Rise from the Late 19th to the Early 21st Century

We estimate the rise in global average sea level from satellite altimeter data for 1993–2009 and from coastal and island sea-level measurements from 1880 to 2009. For 1993–2009 and after correcting for glacial isostatic adjustment, the estimated rate of rise is 3.2 ± 0.4 mm year−1 from the satellite data and 2.8 ± 0.8 mm year−1 from the in situ data. The global average sea-level rise from 1880 to 2009 is about 210 mm. The linear trend from 1900 to 2009 is 1.7 ± 0.2 mm year−1 and since 1961 is 1.9 ± 0.4 mm year−1. There is considerable variability in the rate of rise during the twentieth century but there has been a statistically significant acceleration since 1880 and 1900 of 0.009 ± 0.003 mm year−2 and 0.009 ± 0.004 mm year−2, respectively. Since the start of the altimeter record in 1993, global average sea level rose at a rate near the upper end of the sea level projections of the Intergovernmental Panel on Climate Change’s Third and Fourth Assessment Reports. However, the reconstruction indicates there was little net change in sea level from 1990 to 1993, most likely as a result of the volcanic eruption of Mount Pinatubo in 1991.

Is There Evidence Yet of Acceleration in Mean Sea Level Rise around Mainland Australia?

WATSON, P.J., 2011. Is there evidence yet of acceleration in mean sea level rise around mainland Australia? Journal of Coastal Research, 27(2), 368–377. West Palm Beach (Florida), ISSN 0749-0208. As an island nation with some 85% of the population residing within 50 km of the coast, Australia faces significant threats into the future from sea level rise. Further, with over 710,000 addresses within 3 km of the coast and below 6-m elevation, the implication of a projected global rise in mean sea level of up to 100 cm over the 21st century will have profound economic, social, environmental, and planning consequences. In this context, it is becoming increasingly important to monitor trends emerging from local (regional) records to augment global average measurements and future projections. The Australasian region has four very long, continuous tide gauge records, at Fremantle (1897), Auckland (1903), Fort Denison (1914), and Newcastle (1925), which are invaluable for considering whether there is evidence that the rise in mean sea level is accelerating over the longer term at these locations in line with various global average sea level time-series reconstructions. These long records have been converted to relative 20-year moving average water level time series and fitted to second-order polynomial functions to consider trends of acceleration in mean sea level over time. The analysis reveals a consistent trend of weak deceleration at each of these gauge sites throughout Australasia over the period from 1940 to 2000. Short period trends of acceleration in mean sea level after 1990 are evident at each site, although these are not abnormal or higher than other short-term rates measured throughout the historical record.

Warming of Global Abyssal and Deep Southern Ocean Waters between the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise Budgets*

Abstract Abyssal global and deep Southern Ocean temperature trends are quantified between the 1990s and 2000s to assess the role of recent warming of these regions in global heat and sea level budgets. The authors 1) compute warming rates with uncertainties along 28 full-depth, high-quality hydrographic sections that have been occupied two or more times between 1980 and 2010; 2) divide the global ocean into 32 basins, defined by the topography and climatological ocean bottom temperatures; and then 3) estimate temperature trends in the 24 sampled basins. The three southernmost basins show a strong statistically significant abyssal warming trend, with that warming signal weakening to the north in the central Pacific, western Atlantic, and eastern Indian Oceans. Eastern Atlantic and western Indian Ocean basins show statistically insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic seas, the rate of abyssal (below 4000 m) global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0.027 (±0.009) W m−2 applied over the entire surface of the earth. Deep (1000–4000 m) warming south of the Subantarctic Front of the Antarctic Circumpolar Current adds 0.068 (±0.062) W m−2. The abyssal warming produces a 0.053 (±0.017) mm yr−1 increase in global average sea level and the deep warming south of the Subantarctic Front adds another 0.093 (±0.081) mm yr−1. Thus, warming in these regions, ventilated primarily by Antarctic Bottom Water, accounts for a statistically significant fraction of the present global energy and sea level budgets.

Sea level at Saint Paul Island, southern Indian Ocean, from 1874 to the present

A data archeology exercise was carried out on sea level observations recorded during the transit of Venus across the Sun observed in 1874 from Saint Paul Island (38°41′S, 77°31 E) in the southern Indian Ocean. Historical (1874) and recent (1994–2009) sea level observations were assembled into a consistent time series. A thorough check of the data and its precise geodetic connection to the same datum was only possible thanks to the recent installation of new technologies (GPS buoy and radar water level sensor) and leveling campaigns. The estimated rate of relative sea level change, spanning the last 135 years at Saint Paul Island, was not significantly different from zero (−0.1 ± 0.3 mm yr−1), a value which could be reconciled with estimates of global average sea level rise for the 20th century assuming the DORIS vertical velocity estimate at Amsterdam Island (100 km distant) could be applied to correct for the land motion at the tide gauge. Considering the scarcity of long‐term sea level data in the Southern Hemisphere, the exercise provides an invaluable additional observational constraint for further investigations of the spatial variability of sea level change, once vertical land rates can be determined.

Spatial variability of sea level rise due to water impoundment behind dams

Dams have impounded ∼10,800 km3 of water since 1900, reducing global sea level by ∼30.0 mm and decreasing the rate of sea level rise. The load from impounded water depresses the earth's surface near dams and elevates the geoid, which locally increases relative sea level (RSL). We computed patterns of dam‐induced RSL change globally, and estimated that tide gauges, which are often close to dams, recorded only ∼60% of the global average sea level drop due to reservoir building. Thus, RSL in the globally averaged ocean rose ∼0.2 mm/yr more slowly than has been recorded by tide gauges, or ∼10% slower than the measured rise rate of 1.5–2.0 mm/yr. Relative proximity to dams caused RSL to rise fastest in northeastern North America and slowest in the Pacific. This dam‐induced spatial variability may mask the sea level “fingerprint” of melting sources, especially northern (Greenland) sources of glacial unloading.

Deglaciation-Induced Spatially Variable Sea Level Change: A Simple-Model Case Study for the Greenland and Antarctic Ice Sheets

Some studies on deglaciation-induced sea level change provide only a global average change, thus neglecting the fact that sea level change is spatially variable. This is due mainly to the gravitational and visco-elastic feedback effects of the changing surface mass loads. In order to address this apparent misconception and raise further awareness, we provide a conceptual example based on a simulated total melt of the Greenland and Antarctic ice sheets. This would give a global average sea level change of about 64 m. However, due to the changed distribution of gravitating masses, the sea-level change depends on location, with a range of about −27 m to +79 m (i.e., sea-level will even fall in some places). This spatial dependency has several implications, such as >10% biases in global average sea-level change estimates based only on tide-gauge records, flooding of almost 10% of current land areas, an increase of the length of day by almost a half a second and a northward move of the centre of mass (geocentre) by about 20 m.

Tide gauge and GPS measurements of crustal motion and sea level rise along the eastern margin of Adria

We use observations from tide gauges and colocated continuous GPS (CGPS) stations to investigate crustal deformation and sea level changes along the eastern margin of the Adriatic Sea. We develop a new method to separate common‐mode relative sea level from spatially variable signals. Precise vertical crustal motions determined by CGPS allow us to further separate relative sea level into absolute sea level changes and crustal motions with respect to a local Central Mediterranean–fixed GPS‐defined reference frame. From the tide gauge data, we find fairly uniform relative sea level rise along the coast, with mean rate of 0.84 ± 0.04 mm/yr and weighted RMS variation about this mean of 0.2 mm/yr. This rate is a factor of 2–4 lower than estimates for global average sea level rise. In contrast, vertical motion of coastal rocks determined by CGPS vary appreciably from an average of −1.7 ± 0.4 mm/yr in southern Adria to 0.0 ± 0.4 mm/yr in northern Adria. This difference in crustal motion between the northern and southern regions is independent of our ability to separate sea level from crustal motion, and may be explained by crustal strain associated with an active thrust fault accommodating southern Adria microplate convergence with Eurasia. Enigmatically, the combination of tide gauge and CGPS measurements shows that absolute sea level relative to the GPS‐determined reference frame varies by as much as ∼1.8 mm/yr along the Croatian coast in such a way that the relative sea level remains roughly constant. There are several potential explanations for this result deriving from ocean, atmosphere, and solid Earth dynamics.

Rising seas and retreating coastlines

Any rise in the mean sea level will result in the retreat of unprotected coastlines(Bruun 1962). Fortunately, the still-stand (slow) conditions of global average sealevel rise (SLR) during the last century has resulted in slow and mostly manageablecoastline retreat (recession). Alarmingly, however, recent research indicates that theglobal average sea levels may rise at an unprecedented rate during the twenty-firstcentury (Leuliette et al. 2004; Beckley et al. 2007). The latest IPCC projections (IPCC2007) indicate an SLR range from 0.18 to 0.79 m by 2090–2099 relative to 1980–1999, including an allowance of 0.2 m for uncertainty associated with ice sheet flow.Very recent research (Rahmstorf et al. 2007) also suggests that the measured SLRover the last decade was following the upper range SLR projections given in theIPCC Third Assessment Report (TAR) and the IPCC Fourth Assessment Report(AR4) (Note: The upper range TAR projections are very close to the upper rangeAR4 projections when the ice sheet contributions are considered). Furthermore,Rhamstorf (Rahmstorf 2007) suggests that higher SLR rates than those projectedby IPCC TAR and AR4 may also be possible. In comparison, the global averagerate of SLR during the twentieth century was 1–2 mm/year (Church and White 2006;Douglas et al. 2000). This means that the SLR during the twenty-first century couldbe as much as eight times higher than that during the last century, which in turnis likely to result in much faster coastline recession in the twenty-first century. Thesocio-economic impact of such accelerated coastal recession could be massive due tothe unprecedented growth of coastal communities over the last 50 years or so whichhas led to $ billions worth of developments and infrastructure within the coastal zone.To ensure the safety of growing coastal communities and to avoid massive economic

Irreversible climate change due to carbon dioxide emissions

The severity of damaging human-induced climate change depends not only on the magnitude of the change but also on the potential for irreversibility. This paper shows that the climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop. Following cessation of emissions, removal of atmospheric carbon dioxide decreases radiative forcing, but is largely compensated by slower loss of heat to the ocean, so that atmospheric temperatures do not drop significantly for at least 1,000 years. Among illustrative irreversible impacts that should be expected if atmospheric carbon dioxide concentrations increase from current levels near 385 parts per million by volume (ppmv) to a peak of 450-600 ppmv over the coming century are irreversible dry-season rainfall reductions in several regions comparable to those of the "dust bowl" era and inexorable sea level rise. Thermal expansion of the warming ocean provides a conservative lower limit to irreversible global average sea level rise of at least 0.4-1.0 m if 21st century CO(2) concentrations exceed 600 ppmv and 0.6-1.9 m for peak CO(2) concentrations exceeding approximately 1,000 ppmv. Additional contributions from glaciers and ice sheet contributions to future sea level rise are uncertain but may equal or exceed several meters over the next millennium or longer.

The Beat

The Beat

Evidence for the accelerations of sea level on multi‐decade and century timescales

AbstractA modification in the rate of change of sea level (i.e. an ‘acceleration’ or ‘nonlinear trend’) is an important climate‐related signal, which requires confirmation and explanation. In this study, the evidence for accelerations in regional and global average sea level on timescales of several decades and longer is reviewed by inter‐comparison of the recent findings of different researchers and by inspection of original tide gauge records. Most sea‐level data originate from Europe and North America, and both the sets display evidence for a positive acceleration, or ‘inflexion’, around 1920–1930 and a negative one around 1960. These inflexions are the main contributors to reported accelerations since the late 19th century, and to decelerations during the mid‐ to late 20th century. However, these characteristic features are not always found in records from other parts of the world. Although some aspects of the sea‐level time series are consistent with changes in rates of globally averaged temperature changes, volcanic eruptions and natural climate variability, modelling undertaken so far has been unable to describe these features adequately. This emphasizes the need for a major enhancement of the sea‐level data set, especially for those parts of the world without long tide gauge records, in order to obtain greater insight into the spatial dependence of accelerations. A number of complementary methods must be employed, of which salt marsh techniques offer the possibility of obtaining time series similar to those that would have been obtained from coastal tide gauges. Copyright © 2008 Royal Meteorological Society

A Closer Look at the IPCC Report

A Closer Look at the IPCC Report

Protecting health from climate change

Protecting health from climate change