The entire July issue (Volume 2 No 7 pp447-528) has a focus on sea level.
In their report published in 2007, the Intergovernmental Panel on Climate Change projected that sea level is likely to rise between 18 and 59 centimetres by 2100, threatening the homes and livelihoods of millions who live in low-lying and deltaic regions. This focus draws together studies of past and present sea-level change, and predictions for future fluctuations, as well as presenting insights into the challenges facing coastal communities.
Editorial: Adjustable Adaptation doi:10.1038/ngeo576, ( PDF 303KB)
Humans have been responding to fluctuating sea levels for millennia. Adapting to future change will require a swift start on developing innovative infrastructure while keeping the option to adjust in the long term.
Review Article: Identifying the causes of sea-level change , (PDF 442KB), doi: 10.1038/ngeo544
Global mean sea-level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades. This tenfold increase in the rate of rise can be attributed to climate change through the melting of land ice and the thermal expansion of ocean water. As the present warming trend is expected to continue, global mean sea level will continue to rise. Here we review recent insights into past sea-level changes on decadal to millennial timescales and how they may help constrain future changes. We find that most studies constrain global mean sea-level rise to less than one metre over the twenty-first century, but departures from this global mean could reach several decimetres in many areas. We conclude that improving estimates of the spatial variability in future sea-level change is an important research target in coming years.
A team from the National Oceanography Centre, Southampton (NOCS), along with colleagues from Tübingen (Germany) and Bristol presents a novel continuous reconstruction of sea level fluctuations over the last 520 thousand years. Comparison of this record with data on global climate and carbon dioxide (CO2) levels from Antarctic ice cores suggests that even stabilisation at today’s CO2 levels may commit us to sea-level rise over the next couple of millennia, to a level much higher than long-term projections from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). …
Nature GeoScience: Antarctic temperature and global sea level closely coupled over the past five glacial cycles doi:10.1038/ngeo557
Ice cores from Antarctica record temperature and atmospheric carbon dioxide variations over the past six glacial cycles. … Our record reveals a strong correlation on multi-millennial timescales between global sea level and Antarctic temperature, which is related to global temperature.
Melting Greenland Ice Sheets May Threaten Northeast United States, Canada
Melting of the Greenland ice sheet this century may drive more water than previously thought toward the already threatened coastlines of New York, Boston, Halifax, and other cities in the northeastern United States and Canada, according to new research led by the National Center for Atmospheric Research (NCAR).
The study, which is being published Friday in Geophysical Research Letters, finds that if Greenland’s ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12 to 20 inches (about 30 to 50 centimeters) more than in other coastal areas. The research builds on recent reports that have found that sea level rise associated with global warming could adversely affect North America, and its findings suggest that the situation is more threatening than previously believed. …
The potential for future rapid sea-level rise is perhaps the greatest threat from global warming. But the question of whether recent ice loss from Greenland and Antarctica is the first indication of such a rise is difficult to answer given the limited duration of the instrumental record. New evidence from an exceptionally exposed fossil reef in the Xcaret theme park in Mexico provides a detailed picture of the development of reef terraces, erosion surfaces and sea-level excursions in the region during the last interglacial. A combination of precise uranium-series dating and stratigraphic analysis, together with comparison with coral ages elsewhere, suggests that a sea-level jump of 2 to 3 metres occurred about 121,000 years ago, consistent with an episode of ice-sheet instability towards the end of the last interglacial. On that evidence, sustained rapid ice loss and sea-level rise in the near future are possible.
The letter to Nature is available here:
CBCnews.ca reports that “the researchers were able to estimate that a two-metre sea level change occurred in just 50 years.“.
Nature: High rates of sea-level rise during the last interglacial period, , doi:10.1038/ngeo.2007.28
The last interglacial period, Marine Isotope Stage (MIS) 5e, was characterized by global mean surface temperatures that were at least 2 °C warmer than present. Mean sea level stood 4–6 m higher than modern sea level with an important contribution from a reduction of the Greenland ice sheet. … Although some fossil reef data indicate sea-level fluctuations of up to 10 m around the mean, so far it has not been possible to constrain the duration and rates of change of these shorter-term variations. Here, we use a combination of a continuous high-resolution sea-level record, based on the stable oxygen isotopes of planktonic foraminifera from the central Red Sea1 and age constraints from coral data to estimate rates of sea-level change during MIS-5e. We find average rates of sea-level rise of 1.6 m per century. As global mean temperatures during MIS-5e were comparable to projections for future climate change under the influence of anthropogenic greenhouse-gas emissions, these observed rates of sea-level change inform the ongoing debate about high versus low rates of sea-level rise in the coming century.
The University of Copenhagen is hosting an international scientific congress on climate change, 10-12 March 2009 in Copenhagen, Denmark.
“Climate change represents a clear and unprecedented challenge for human society. This symposium focuses on providing a synthesis of existing and emerging scientific knowledge necessary in order to make intelligent societal decisions concerning application of mitigation and adaptation strategies in response to climate change. The symposium aims to identify and synthesise the science, technology and policy advances required in order to ensure sustainability of global communities in the current and coming decades”
From their first press conference: Rising sea levels set to have major impacts around the world
– Even the lower ranges of the plausible sea level rise are likely to hit low lying countries hard
The last assessment report from the IPCC from 2007 projected a sea level rise of 18 – 59 centimeter. However the report also clearly stated that not all factors contributing to sea level rise could be calculated at that time. The uncertainty was centered on the ice sheets, how they react to the effects of a warmer climate and how they interact with the oceans, explains Eric Rignot, Professor of Earth System Science at the University of California Irvine and Senior Research Scientist at NASA’s Jet Propulsion Laboratory. “The numbers from the last IPCC are a lower bound because it was recognized at the time that there was a lot of uncertainty about ice sheets. The numerical models used at the time did not have a complete representation of outlet glaciers and their interactions with the ocean. The results gathered in the last 2-3 years show that these are fundamental aspects that cannot be overlooked. As a result of the acceleration of outlet glaciers over large regions, the ice sheets in Greenland and Antarctica are already contributing more and faster to sea level rise than anticipated. If this trend continues, we are likely to witness sea level rise one meter or more by year 2100”, he says.
These data globes, created with radar altimeter measurements from Topex/Poseidon and Jason-1, represent 14 years of science data delivered by these satellites during their continuing voyage of discovery. Launched on August 10, 1992, Topex/Poseidon was the first great oceanographic research vessel to sail into space. Its follow-on, Jason-1, launched on December 7, 2001, continues making the precise measurements of the ocean surface begun by Topex/Poseidon.
The globes show the average annual sea-surface height anomalies for the period from 1993 to 2006. An anomaly is the difference between the height of the sea surface measured by the satellites and the average sea-surface height. Sea-surface heights move up and down in a slow, regular pattern as the Sun warms the water of the upper ocean and as the seasons progress. This “normal” annual signal has been removed from these maps to show clearly the large year-to-year variations.
Sea-surface height reflects how much heat is stored in the upper ocean, an important factor in climate. In these images, “normal” sea-surface height appears as green. The blue and purple areas represent heights that are between 8 and 24 centimeters (3 and 9 inches) lower than normal and indicate cooler water. Red and white areas represent ocean heights that are between 8 and 24 centimeters (3 and 9 inches) higher than normal and indicate warmer water
The NASA Jet Propulsion Laboratory has a page dedicated to El Niño/La Niña & PDO (Pacific Decadal Oscillation), and offers the following comments about the PDO:
The Pacific Decadal Oscillation (PDO) is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years. From TOPEX/Poseidon data (see below) together with other oceans and atmospheres data, scientists think we have just entered the ‘cool’ phase. The ‘cool’ phase is characterised by a cool wedge of lower than normal sea-surface heights/ocean temperatures in the eastern equatorial Pacific and a warm horseshoe pattern of higher than normal sea-surface heights connecting the north, west and southern Pacific. In the ‘warm’ or ‘positive’ phase, which appears to have lasted from 1977- 1999, the west Pacific Ocean becomes cool and the wedge in the east warms.
For an in-depth discussion about sea level rise, visit CSIRO in Australia.
We love the coast. Coastal regions, particularly some low-lying river deltas, have very high population densities. In excess of 150 million people live within 1 metre of high tide level, and 250 million within 5 metres of high tide. There are billions of dollars invested in coastal infrastructure immediately adjacent to the coast. Many of the world’s mega cities (populations of many millions) are on the coast.
Sea level is rising as a result of increasing concentration of greenhouse gases in the atmosphere. Sea level rise contributes to coastal erosion and inundation of low-lying coastal regions, particularly during extreme sea level events. It also leads to saltwater intrusion into aquifers, deltas and estuaries. These changes impact on coastal ecosystems, water resources, and human settlements and activities. Regions at most risk include heavily populated deltaic regions, small islands (especially coral atolls), and sandy coasts backed by major coastal developments.
On this web site, we attempt to bring together information on sea level rise and its causes. We also include our estimates of global and regional sea level, links to other web pages and data sets and a list of our publications.
This uses data downloaded from the CSIRO site showing consolidated tide gauge and satellite data and a linear least squares fit for three periods. The period 1870 to 1924 saw sea levels rise by about 0.83 millimeters per year; from 1925 to 1985 by 2.00 mm/yr; and from 1986 to 2008 by 3.23 mm/yr. From this is can been seen that there’s an acceleration in the rise, which cannot be attributed to continental “glacial rebound” since the last ice age. It is most likely caused by thermal expansion and ice-sheet melting due to rising temperatures.
The calculated 3.23 mm/yr rate corresponds very closely with the rate shown independently from the Ocean Surface Topography Mission :
New Oceanography Mission Data Now Available – 12.16.08
PASADENA, Calif. — Oceanography data that will help scientists around the world better understand climate change are now available. The data come from the Ocean Surface Topography Mission, also known as OSTM/Jason-2, a spacecraft developed jointly by NASA and the French space agency.
Launched June 20, 2008, the mission’s first validated data products in support of improved weather, climate and ocean forecasts are now being distributed to the public within a few hours of observation. Beginning in 2009, other data products for climate research will be available a few days to a few weeks after observations are taken by the satellite. …
“Sea level is rising at a rate of 0.13 inches per year [3.30 mm/yr], nearly twice as fast as the previous 100 years,” said Laury Miller, chief of NOAA’s Laboratory for Satellite Altimetry in Silver Spring, Md. “If this rate continues unchanged during the coming decades, it will have a huge impact on erosion and flooding in coastal regions…”
University of Alaska Fairbanks (UAF): Study: Greenland ice sheet larger contributor to sea-level rise
The Greenland ice sheet is melting faster than expected according to a new study led by a University of Alaska Fairbanks researcher and published in the journal Hydrological Processes.
Study results indicate that the ice sheet may be responsible for nearly 25 percent of global sea rise in the past 13 years. The study also shows that seas now are rising by more than 3 millimeters a year–more than 50 percent faster than the average for the 20th century.
UAF researcher Sebastian H. Mernild and colleagues from the United States, United Kingdom and Denmark discovered that from 1995 to 2007, overall precipitation on the ice sheet decreased while surface ablation–the combination of evaporation, melting and calving of the ice sheet–increased. According to Mernild’s new data, since 1995 the ice sheet lost an average of 265 cubic kilometers per year, which has contributed to about 0.7 millimeters per year in global sea level rise. These figures do not include thermal expansion–the expansion of the ice volume in response to heat–so the contribution could be up to twice that. …
The research article is published in the Wiley Interscience journal “Hydrological Processes”: Greenland Ice Sheet surface mass-balance modelling and freshwater flux for 2007, and in a 1995-2007 perspective
Recent projections of sea-level rise after a future collapse of the West Antarctic Ice Sheet for example, the Fourth Intergovernmental Panel on Climate Change Assessment Report) assume that meltwater will spread uniformly (that is, eustatically) across the oceans once marine-based sectors of the West Antarctic are filled. A largely neglected 1977 study predicted that peak values would be 20% higher than the eustatic in the North Pacific and 5 to 10% higher along the U.S. coastline. We show, with use of a state-of-the-art theory, that the sea-level rise in excess of the eustatic value will be two to three times higher than previously predicted for U.S. coastal sites.
Supporting online material
Article from “ScienceDaily“
University of Toronto and Oregon State University geophysicists have shown that should the West Antarctic Ice Sheet collapse and melt in a warming world – as many scientists are concerned it will – it is the coastlines of North America and of nations in the southern Indian Ocean that will face the greatest threats from rising sea levels.
Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.
Supporting online material
From the Science Podcast [mp3]: an interview with Jonathan Bamber on a reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet.
Today (2011-05-25) at the Globe and Mail Richard Wakefield pointed me to the Europe Envisat data and a website showing a very recent (since the beginning of 2010) sea level decline Sea Level Decline During The “Hottest Year Ever” With “Record Greenland Melt”.
The following is a graph of all of the data points with a 12-month running average to filter out seasonal variability. It appears to me that the remaining variability is no different from many past events as shown in Sea Level Fig. 4 Sea Level Longterm Trends above.
Data source: ftp://ftp.aviso.oceanobs.com/pub/oceano/AVISO/indicators/msl/MSL_Serie_EN_Global_NoIB_RWT_NoGIA_NoAdjust.txt