The melting rate of the Antarctic ice sheet is mainly controlled by the increase of ocean temperatures surrounding Antarctica. Using a new, higher-resolution climate model simulation, scientists from Utrecht University found a much slower ocean temperature increase compared to current simulations with a coarser resolution. Consequently, the projected sea-level rise in 100 years is about 25% lower than expected from the current simulations. These results are published today in the journal Science Advances.https://65cf01d7103f8788f2c2aecbe76ab80c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html
Estimates for future sea-level rise are based on a large ensemble of climate model simulations. The output from these simulations helps to understand future climate change and its effects on the sea level. Climate researchers continually aim to improve these models, for example by using a much higher spatial resolution that takes more details into account. “High-resolution simulations can determine the ocean circulation much more accurately,” says Prof. Henk Dijkstra. Together with his Ph.D. candidate René van Westen, he has been studying ocean currents in high-resolution climate model simulations over the past few years.
The new high-resolution model takes into account ocean eddy processes. An eddy is a large (10-200 km) swirling and turbulent feature in the ocean circulation, which contributes to the transport of heat and salt. Adding ocean eddies into the simulation leads to a more realistic representation of the ocean temperatures surrounding Antarctica, which is key for determining the mass loss of the Antarctic ice sheet. “The Antarctic ice sheet is surrounded by ice shelves which reduce the flow of land ice into the ocean,” Van Westen explains. “Higher ocean temperatures around Antarctica increase the melting of these ice shelves, resulting in an acceleration of land ice into the ocean and consequently leading to more sea-level rise.”https://www.youtube.com/embed/a9m61TsJDa0?color=whiteComparison of the new high-resolution model (left) with the previously used low-resolution one (right). Credit: Utrecht University
The current climate model simulations, which do not take ocean eddies into account, project that the ocean temperatures around Antarctica are increasing under climate change. The new high-resolution simulation shows quite different behavior and some regions near Antarctica even cool under climate change. “These regions appear to be more resilient under climate change,” says Van Westen. Dijkstra adds: “One obtains a very different temperature response due to ocean-eddy effects.”
The new high-resolution model projects a smaller mass loss as a result of ice-shelf melt: only one third compared to current climate models. This reduces the projected global sea-level rise by 25% in the upcoming 100 years, Van Westen mentions. “Although sea levels will continue to rise, this is good news for low-lying regions. In our simulation, ocean eddies play a crucial role in sea-level projections, showing that these small-scale ocean features can have a global effect.”
It took the team about one year to complete the high-resolution model simulation on the national supercomputer at SURFsara in Amsterdam. Dijkstra: “These high-resolution models require an immense amount of computation, but are valuable as they reveal smaller-scale physical processes which should be taken into account when studying climate change.”
A team of scientists, led by researchers from Durham University, used geological records of past sea levels to shed light on the ice sheets responsible for a rapid pulse of sea-level rise in Earth’s recent past.
Geological records tell us that, at the end of the last ice age around 14,600 years ago, sea levels rose at ten times the current rate due to Meltwater Pulse 1A (MWP-1A); a 500 year, ~18 meter sea-level rise event.
Until now, the scientific community has not been able to agree about which ice sheet was responsible for this rapid rise, with the massive Antarctic Ice Sheet being a likely suspect, but some evidence pointing towards ice sheets in the Northern Hemisphere.
The new study uses detailed geological sea-level data and state-of-the-art modelling techniques to reveal the sources of MWP-1A. Interestingly, most of the meltwater appears to have originated from the former North American and Eurasian ice sheets, with minimal contribution from Antarctica, reconciling formerly disparate views.
In addition to flooding vast areas of low-lying land, this unparalleled discharge of freshwater into the ocean—comparable to melting an ice sheet twice the size of Greenland in only 500 years—will have disrupted ocean circulation, with knock-on effects for global climate. Knowing the source of the meltwater will improve the accuracy of climate models that are used to replicate the past and predict changes in the future.
The results are important for our understanding of ice-ocean-climate interactions which play a significant role in shaping terrestrial weather patterns. The findings are particularly timely with the Greenland ice sheet rapidly melting, contributing to a rise in sea levels and changes to global ocean circulation.
Of the findings, lead author Yucheng Lin, in the Department of Geography at Durham University notes: “Despite being identified over 30 years ago, it has been surprisingly challenging to determine which ice sheet was the major contributor to this dramatic rise in sea levels.
“Previously, scientists tried to work out the source of the sea-level rise based on sea-level data from the tropics, but the majority of those studies disagreed with geological records of ice sheet change.
Our study includes novel information from lakes around the coast of Scotland that were isolated from the ocean due to land uplift following the retreat of the British Ice Sheet, allowing us to confidently identify the meltwater sources.”
Co-author Dr. Pippa Whitehouse, in the Department of Geography at Durham University said “The technique we have used allows us to really dig into the error bars on the data and explore which ice-melt scenarios were most likely.
“We found that most of the rapid sea-level rise was due to ice sheet melt across North America and Scandinavia, with a surprisingly small contribution from Antarctica.
“The next big question is to work out what triggered the ice melt, and what impact the massive influx of meltwater had on ocean currents in the North Atlantic. This is very much on our minds today—any disruption to the Gulf Stream, for example due to melting of the Greenland Ice Sheet, will have significant consequences for the UK climate.”
Rising sea levels due to warming climate pose a great risk to society, improving our understand of why and how fast change could happen will help us plan for the impacts.
Updated 9:41 AM ET, Fri March 26, 2021Rising water caused by Hurricane Sandy rushes into the Carey Tunnel (formerly the Brooklyn-Battery Tunnel), on October 29, 2012 in New York City.
(CNN)Along a stretch of the East Coast that includes New York City, sea-level rise has increased at its fastest rate in the prior 100 years compared to the past 2,000 years, according to a new study led by Rutgers University.”The global rise in sea-level from melting ice and warming oceans from 1900 to 2000 led to a rate that’s more than twice the average for the years 0 to 1800 — the most significant change,” Rutgers said of the study’s findings.The study uses new techniques and focuses on six specific locations in the northeastern US, including three in New Jersey and one each in Connecticut, New York and North Carolina.Human-induced climate change is fueling this more dramatic rise. The research shows that emissions of carbon dioxide and other greenhouse gases by humans burning fossil fuels have warmed up our planet, causing the oceans to warm and glaciers to melt.
Sea-level ‘budgets’ break down contributors to rising water
This research is the first of its kind to utilize what the researchers call “sea-level budgets” while determining the rate at which the ocean is rising over an extensive period.close dialog
Sea level rise is increasing fastest in populous coastal areas, study saysThe study found that southern New Jersey has had the largest sea-level rise in the past 2,000 years because of sinking land.This land subsidence “is from the effect of the Laurentide ice sheet from our last Ice Age,” Walker told CNN. “The ice sheet retreated thousands of years ago, and the land is still readjusting from the effect of that past sheet.”There are also other factors, which include groundwater extraction and changing ocean currents.”US East Coast sea level rise rates are elevated because of the slowing Gulf Stream,” said Brian McNoldy, a senior research associate at the University of Miami Rosenstiel School of Marine and Atmospheric Science, who was not part of the study.Walker added that over the past 200 years roughly, “We have rates that are double the average, compared to the last 2,000 years … Where it used to be this regional land sinking being the dominant force, now it’s this global component, which is driven by the ice melt and warming of the oceans.”These graphics show the sea level rise rates over time by each sea-level budget. The light gray resembles the most dominant budget, linear. This category factors in land subsidence caused by the natural compaction of land and the Laurentide ice sheet melting. The pie charts also highlights how the linear sea-level budget is the largest component of sea-level rise in New Jersey. The other shadings on the graphs signify the three other sea-level budgets: global (red), regional non-linear (light blue) and local (purple). The dashed black line on the graphs shows the total sea level rise when combining these four budgets.At this global scale, sea level rise was found to have been primarily caused by “increased ocean mass and volume from glacier and ice sheet melt and thermal expansion on a global scale in response to greenhouse forcing of warming sea surface and surface air temperatures,” the research states.While the sea-level budgets have risen in at least the past century, over time some have fallen, too. Prior to around 1600 of the Common Era, the regional non-linear budget had a decreasing sea level rate. These lowering sea levels are likely caused by “broad climate transitions in the North Atlantic,” according to the research. This includes pressure patterns over the North Atlantic, which basically is where the low and high pressure systems are located.
Climate change is causing rates to accelerate
These global factors were not a dominant contributor to sea-level rise prior to the year 1800, but that has changed in recent times. “The increasing influence of the global component is the most significant change in the sea-level budgets at all six sites,” according to the study.This means that humans are causing the seas to rise and that they are dominating Earth’s systems, scientists say.The data collected for a location in northern New Jersey shows that from 1400 to 1500 CE, global budget sea levels likely rose at a rate of 0.13 millimeters per year. A few hundred years later in the period from 1900 to 2000, or the 20th century, the rate increased drastically to 1.30 millimeters per year.Meanwhile, the regional and local sea-level budgets were either constant or had significantly lower changes.At the global scale, for example, there have been rises in sea level over the course of several centuries but then falls. This is a natural cycle. But what has been happening recently in the 20th century has not been completely natural due to a more significant, upward acceleration of water levels.Walker said trends in rising sea levels can be linked to the greenhouse gases already emitted, and that rates will continue to accelerate.
Flood risk is growing for US homeowners due to climate change. Current insurance rates greatly underestimate the threat, a new report findsThis acceleration will increase the number of days per year of flooding events, sometimes known as sunny-day floods. Tidal cycles can play a role in this, including the King Tides in the fall that produce the highest tidal levels of the year. Combine that with rising seas and that will lead to more coastal flooding days, regardless of the weather.There is another component to how sea level rise can have a big impact: large storms. Walker noted, “With these big storm events, you can really see the impacts more greatly.”A storm like Hurricane Sandy in 2012 crippled much of the Northeast, including New York City, with record storm surge. “The impacts from a big storm like that are just going to be exacerbated on top of (the rising seas).”Walker said the effects of sea level rise during significant weather events pose a longer-term challenge once the levels do get even higher.
Updated 8:12 PM ET, Tue March 9, 2021This aerial picture shows people rowing a raft over a flooded road in Jakarta on February 20, 2021, following heavy overnight rains. The combination of so many people and the multitude of rivers has made this city especially prone to relative sea level rise.
(CNN)Coastal communities are experiencing sea level rise four times worse than global water rise, according to a new study released Monday.Groundwater pumping, extraction of materials from the ground and sediment production are all happening near the coasts and that is causing the land to actually sink — compounding the effects of a rising sea level.It is no coincidence that these are the same locations where people live, worsening the impacts and increasing the vulnerability.Many of the largest, most populated cities in the world are built along the deltas of major rivers, where there is the added exposure of rivers connecting to the ocean.Content by BabbelMake 2021 the year you learn a new languageThis language learning service is designed to get you conversational in a new language in just 3 weeks, no matter your skill level or prior experience.Much of the coast is uninhabited by people, but where there is civilization, there tends to be a greater rise in water levels.According to the study, it quantifies “global-mean relative sea-level rise to be 2.5 mm per year over the past two decades. However, as coastal inhabitants are preferentially located in subsiding locations, they experience an average relative sea-level rise up to four times faster at 7.8 to 9.9 mm per year.”
Coastal lands are sinking
This is the first ever study that factors in land subsidence into current sea level rise observations globally.close dialog
The slowing down of ocean currents could have a devastating effect on our climate“But we have this additional process that is making things even worse. And of course, these things add up. It doesn’t really matter whether the sea rises or the land sinks, the people living on the coast still have the same impacts.”Sea level rise is happening in many parts of the world. Where the land is rising, sea level rise is not as significant. Not as many people live where the land is rising, however.But where the land sinks, the relative rise of the sea is higher — and unfortunately that is where people tend to live. In fact, more than one in five people live along the coastline where the sea level is increasing at 10 mm (or 0.4 inches) or more per year, despite the fact that it encompasses less than 1% of the world’s coastline.In other parts of the world, like parts of the southeastern US, geological changes are not big contributors.”There’s places where the land isn’t really moving much at all,” said Brian McNoldy, a senior research associate at the University of Miami who was not a part of the study. “And you really are just seeing the effects of ocean levels increasing.”One of the biggest contributors to this subsidence is river deltas.”Deltas are where rivers bring sediment to the sea,” Nicholls said. “And the weight of the sediment plus the compression with the sediment causes consolidation … So you don’t get (rising land) with the deltas, you just get sinking and that can be exacerbated by groundwater withdrawal and drainage.”This global map shows the average relative sea level rise rate in millimeters per year, and is weighted for population (second map). The map is divided into 23 different coastal regions, and the shadings are based on how sea levels are currently rising every year. When weighting the data to population opposed to coastal length (first map), the sea level rise is greater because of human activity that promotes subsidence and loss of elevation. Portions of Asia are experiencing the highest rate of water rise when factoring in both the length average and population average. Source: Nature Climate Change, March 2021″Rapid rates of subsidence in deltas and especially cities on deltas are also human-caused, mostly due to groundwater pumping, also oil and gas extraction, and sediment resupply prevented by upstream dams, flood defenses, sand extraction or mining.”Scientists have already been aware of the implications of human-linked climate change to sea level rise, but now there is research that investigates rising and lowering land also caused by humans.”The process that we’re really talking about here is fundamentally down to where people choose to live. And then the fact that they actually made the subsidence worse.”There is a natural cause of the rising and sinking lands, however. According to the study, the melting ice sheets during the ice age thousands of years ago lead to and is still causing rising land near Hudson Bay in Canada.
Asia experiencing highest rate of sea level rise
Coastal sections of Asia have been the most impacted by sea level rise in relation to land subsidence. That’s because there is a prevalence of deltas and very populous cities.”South, Southeast and East Asia is noteworthy, as these regions collectively contain 71% of the global coastal population below 10 m in elevation,” according to the research.
India’s groundwater crisis threatens food security for hundreds of millions, study says“In Jakarta, subsidences of over 10 centimeters per year — It may be even locally faster than that. You can get very, very large changes, but in very small areas,” Nicholls said. “But they’re important because lots of people live there.”The map below highlights just a few of the many rivers and canals within Jakarta. The combination of so many people and the multitude of rivers has made this city especially prone to relative sea level rise.
Flood CanalSunter RiverCiliwung RiverJakarta, Indonesia
In the US, cities like New Orleans, which is near the Mississippi River delta, are also sinking. This correlates with one of the highest rises in relative sea level in the country.According to NOAA, the greatest relative sea level rise has been measured near coastal Louisiana and southeastern Texas.”A place where the combined effects of sinking land and sea level rise is in the northern Gulf Coast areas, like coastal Louisiana,” said McNoldy, of the University of Miami.In Galveston, Texas, sea levels have risen 6.62 mm per year or about one-quarter of an inch per year during the time period of 1957 to 2011. NOAA said this is “equivalent to a change of 2.17 feet in 100 years.”When asked what can be done about this issue, Nicholls said mitigating the threats of climate change is most crucial.”I think the important thing is we have a great effort, and rightly so, to actually mitigating climate change and the Paris Agreement,” Nicholls said.The report also says reducing groundwater withdrawal and managing deltas can reduce land subsidence.
Estimates of ‘just’ 90 centimeters sea level rise by 2100 ignore Antarctica’s slower but hefty contribution, warns oceanographer John EnglanderShare in FacebookShare in TwitterSend in e-mailSend in e-mailZen ReadPrint article
Glacier on west Greenland in August 2007, as it bends in its normal descent to the sea. Due to warming the melting glacier has retreated far inlandCredit: John EnglanderRuth SchusterGet email notification for articles from Ruth SchusterFollowPublished at 23:48
The vast ice sheet on Greenland has become unstable and technology isn’t storming to the rescue. The world is not on a trajectory to “curb” global warming at 1.5 degrees Celsius – we’re almost there already. “Everybody is asleep. It’s like the Titanic,” wails sea level rise guru John Englander, an oceanographer and author who has made it his life’s mission to shake the world awake before it’s too late.
Too late for what? To secure coastlines all over the world ahead of the rising sea, which is pushing coastlines farther inland. To protect property values, to strategize and reorganize economic priorities, to move seaside nuclear reactors, you name it. Life as we know it.
Part of the reason for the global somnolescence is that scientific reports by nature err on the side of caution. Thus, the current sea level rise estimates for 2050 or 2100 (which distract from the fact that sea level rise will continue afterward) are typically conservative, which in this case means they understate the real rise. It’s also considered rude to conclude that the world is careening toward hell in a handbasket.- Advertisment –
But the world is not on a minimalist trajectory. It is not heading for a “mere” 40-centimeter (16-inch) increase by 2100 based on the optimistic scenario, which is losing credence. The official (UN-IPCC) high end of forecasts is around 90 centimeters by 2100 – but even that is too optimistic in Englander’s view, as he warned in a joint paper with other academics in December: “Twenty-first century sea level rise could exceed IPCC projections for strong-warming futures.”
Sea level rise by 2100 could be 2 meters. It could be 3, or 4 meters, he says. The only thing we know is that we don’t know: the situation is fluid, you should excuse the expression. And we know that a lot of the water will come from Greenland.
To warn the general population, however, Englander feels science’s kid gloves are inappropriate at this point. Mounting evidence indicates climate change is accelerating and creating vicious circles that quicken it even more. The destabilization of Greenland’s ice sheet is a case in point.
It is hard to reconcile reports of its accelerated melting and destabilization with estimates that it will, nonetheless, take maybe five to six centuries for all Greenland’s ice to melt. Englander explains this seeming incongruity.
“I’ve been there several times, leading expeditions,” he tells Haaretz. “It’s hard to comprehend how vast Greenland is. It’s 2,500 kilometers north to south and about 1,000 kilometers east to west, literally from east of the Mississippi in the U.S., and from Maine to Florida” – i.e., nearly 2.2 million square kilometers.- Advertisment –
In Middle Eastern terms, Greenland is about the size of Saudi Arabia. (Israel is about 22,000 square kilometers in area – about twice the size of B-15, the biggest-ever iceberg caught on camera, which calved off the Ross Ice Shelf. )https://www.youtube.com/embed/lBfzFt_kgNU?start=0&controls=1&loop=0&modestbranding=1&rel=1&autoplay=false&enablejsapi=1&mute=undefined
Greenland is covered by a layer of ice 1 to 3 kilometers thick; if it all melts, it will raise global sea levels by over 7 meters. No one thinks that can happen quickly. It will take centuries, at least. “The question is what will happen by 2050 and 2100,” Englander drives home the point.
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Asked if the Greenlandic ice sheet’s recently reported destabilization could change his vague expectation that the melt should take centuries, Englander offers the only answer he can: maybe. Which is all the more reason to wake up.- Advertisment –
Sea level rise cannot be stopped
Even if carbon dioxide emissions were to screen to a halt today, even if cows were to start farting flowers instead of methane, even if every car were to suddenly morph into a tree, further sea level rise is inevitable. Like the Titanic, its direction cannot be diverted anymore, though its momentum might be influenced.
It is time to glance again at John Englander’s famous graph of historic correlations between atmospheric carbon dioxide levels, global mean temperatures, and sea level over the last 400,000 years. The graph shows exactly what the problem is:
Atmospheric carbon dioxide has risen to levels last seen millions of years ago, approximately speaking (neither Donald Trump nor the coronavirus changed the trajectory in any meaningful sense). Atmospheric carbon dioxide concentrations and temperature are correlated: if the one rises, so does the other. The higher the CO2, the higher the global mean temperature – at a lag. Again: at a lag. Temperature has yet to proportionately react to the increase in carbon dioxide levels.
Yes, after CO2 rises, temperature will too – but how long the reaction will take depends on a practically infinite array of parameters, so it cannot be predicted with any meaningful accuracy. All we can say is it will happen, and the fact that the globe has experienced year after year of “record heat” is just the start. Oceans, being vast and dense and saline, take longer to react than the air or shallow lakes, but as the air warms, so does their surface and then their depths. The Arctic has been among the worst affected – there are days parts of it are hotter than in Tel Aviv.
Apropos of which, forecasting the future of Israel’s coast is tricky.
“The coastline has moved kilometers inland over the last 50 years,” says Dr. (emeritus) John K. Hall of the Geological Survey of Israel, adding that this conundrum tends to be met with massive denial. “The beaches are eroding, the cliffs are coming down,” he adds. At sea rise levels of 20 to 30 centimeters, it is difficult to draw lines with any accuracy, to say which neighborhoods will be affected and which spared – but the key issue is the likelihood of increasingly violent storms smashing into the beaches and cliffs. “If sea levels come up, storms will beat the hell out of the coast,” Hall predicts.
Anyway, there is a growing unease in global scientific circles about simultaneously warning and reassuring the public. More and more scientists are warning that sea level will rise faster “than previously thought.” Which means what?
The Greenland ice sheet alone locks up 7 meters of sea level rise, which is bad enough, but Antarctica locks up 65 meters more, Englander explains. All the other glaciers in the world add just 1 more meter. “Looking at glaciers from Mount Kilimanjaro [in Kenya] to the Alps, it’s pocket change” he says.
Ergo: the Arctic island of Greenland and southern continent of Antarctica contain about 98 percent of the ice on land, by volume. Yet modelers have been ignoring Antarctica’s contribution.
This is why? For one thing, because the dynamics and precise timing of Antarctica’s melting ice remain profoundly unclear. As we said, scientists tend to err on the side of caution, lest they be perceived as a pack of yowling Cassandras scorned by policymakers. If you stand on a soapbox shrieking “The end is nigh,” precious few will listen even as avenging angels begin to arrive.
But the result is that projections of half a meter to just-under-a-meter of sea level rise by the century’s end don’t factor in Antarctica, nor do they factor in Greenland’s destabilization, Englander explains.
That is bound to end about as well as the Euripides play performed in 408 B.C.E., where the actor Hegelochus meant to say, “After the storm I see again a calm sea,” but wound up saying, “After the storm I see again a weasel.” Well, 2,500 years belatedly, the unfortunate thespian may have had a point. Those are not calm seas on our horizon.
The Greenlandic irony
What does “Greenland has destabilized” even mean? That parts of the ice sheet and major glaciers are already exhibiting sudden break up and collapse. In 2012, the documentary “Chasing Ice” captured one huge collapse using time-lapse cameras. Meanwhile, Greenland is already the chief contributor to sea level rise today, and it has started to dawn on coastal residents and insurance companies and the like that “something” will have to be done.
Part of Englander’s book due out on April 6, “Moving to Higher Ground” (The Science Bookshelf), discusses exactly these conundrums.
Why is it only an issue now? The science of climate change has been around for decades. Why is anybody still buying a beachside home?
Englander blames a failure of imagination. At the height of the Ice Age, the average sea level was 120 meters lower than it is now. As the latest Ice Age waned and the ice sheets melted, sea levels gradually rose – sometimes more abruptly than at other times. But none of that happened during recorded history.
Civilization as we could recognize it – a gradual transition from hunting-gathering to a settled lifestyle – seems to have begun around 12,000 years ago, some places earlier, some places later, well after the Last Glacial Maximum 22,000 years ago. People adore living by the coast and always have. Even Neanderthals are thought to have frolicked in the water and dived for shellfish. And the first villages on low-lying shoreland were indeed inundated. Israeli archaeologists, for example, have found the remains of Neolithic villages off today’s coast, under the waves of the Mediterranean.
But for the last 7,000 or 8,000 years, sea levels have been stable, near present-day heights, and we are not capable of imagining the situation otherwise, Englander postulates.
Sea levels have been creeping up since the industrial revolution began and some cities have noticed – think of Miami and its sunny-day floods. But that is why we simply cannot fathom what a meter or two even mean. It’s beyond our scope of experience.
The last time sea level was above present-day levels was 122,000 years ago, when it was some 7 meters above present, he explains.
“Even at the accelerated warming rate, most people don’t think we’ll get more than a meter out of sea level rise from Greenland this century. But a meter of global sea level rise would be devastating, flooding literally thousands of coastal communities,” he points out the obvious.
Three of the biggest cities in the world are in acute danger: Shanghai, Mumbai and Jakarta, and so are hundreds more from Alexandria to Boston to London.
Ironically, Greenland’s own coastlines are probably safe. This is because as its ice cover melts, the land is rising, as land does when an enormous weight is lifted. It is the obverse of the situation in Jakarta, where the land is sinking because of groundwater depletion, the heavy buildings and sea level rise. Never mind 2100: the city is expected to be 95 percent underwater by 2050.
“The human instinct is to be optimistic, [to hope] technology will come to the rescue. But it doesn’t make sense in this context,” Englander sums up. “The oceans have been warmed almost a degree already and we’re going to warm them 2 degrees more. The ice is going to melt.”
Sea level rise is not a new phenomenon. For much of the 20th century, the global mean sea level has been inching upward — about 0.05 inches (1.4 millimeters) per year, according to the United Nations’ Intergovernmental Panel on Climate Change. Global mean sea level is an average of all the seas covering the Earth. But during the last two decades, the rate has more than doubled. From 2005 to 2015, sea levels rose by 0.1 inches (3.6 mm) per year.
But is this rise consistent worldwide?
Nope, not at all. “Sea level rise is not very uniform across the globe,” said Kathy McInnes, a senior principal research scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia. She leads the Climate Extremes and Projections Group of CSIRO’s Climate Science Centre.
Many places are experiencing a rise as the global mean rises, but in a few places sea level is falling, said Jacky Austermann, an assistant professor of Earth and environmental sciences at Columbia University’s Lamont-Doherty Earth Observatory in New York. “There’s not a place that’s immune from sea level change,” Austermann told Live Science.
What’s causing sea levels to change? Climate change, mostly. Rising temperatures warm the air and the water. As water warms, it expands. The warm air and water also melts ice sheets. “In Antarctica, warming oceans are the biggest contributor to disintegration of ice sheets,” Austermann said. As the glaciers melt, more water flows into the ocean, thus adding more volume to the seas.
But where does that extra water go? It doesn’t spread out evenly across the globe, McInnes said. Globally, there are two main factors — thermal expansion and the gravitational pull of ice sheets. With thermal expansion, ocean currents redistribute heat, which moves cold and warm water around. “If there’s greater heat in some areas and less heat in others,” warmer ocean areas will expand more, while colder places will have less expansion, McInnes said. Atmospheric winds can also depress and raise oceans, she added. Moreover, those wind patterns are also changing as the planet warms, Live Science previously reported.
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When gigantic ice sheets melt, they don’t just simply add water to the ocean. Mass attracts mass. The Antarctic and Greenland ice sheets are so large that their masses exert a gravitational pull on the sea around them, Austermann said. This makes the sea level a bit higher in those areas. But when the ice sheets melt, their masses reduce, too. As the mass decreases, so does the strength of the gravitational force pulling up the water. In effect, sea levels are falling close to the melting ice sheets, for instance in Greenland, but rising on the opposite side of the world, in this case the Southern Hemisphere, she added. “This pattern of sea level change on the globe, called a sea level fingerprint, is distinct for that particular ice sheet,” Austermann said, explaining how the melting Greenland and Antarctic ice sheets each have their own fingerprint patterns.
Local effects like groundwater pumping, fossil fuel extraction, and compaction of sediment also worsen sea level rise, McInnes said. In some areas, especially cities built on deltas like Tokyo and New Orleans, the land is falling while sea levels rise. “Some of these large mega-deltas are actually sinking at a much faster rate than sea level is rising,” McInnes said. “That’s a double whammy where the land is going down and sea levels are going up at the same time.” RELATED MYSTERIES
Natural climate cycles contribute to sea level rise, too.” El Niño and La Niña cause a see-saw-like effect where all the water piles up on one side of the [Pacific Ocean] basin in one phase, and then piles up on the other side of the basin in the other phase,” McInnes said.
Rising sea levels across the globe may lead to more destructive storm surges and more frequent nuisance flooding, or flooding that causes public inconveniences, for instance road closures. Stormwater drainage systems rely on gravity between the inland area and the ocean to function properly, so if ocean sea levels rise, then water won’t move the right way through drainage system pipes, especially during storms. “If we continue to have storm surges, they will elevate water levels on top of already higher sea levels,” Austermann said. “That’s the most pressing short-term problem regarding sea level rise.”
Sunbathing mothers keep an anxious eye out for children enjoying horseback rides, as groups of young men engage in energetic games of beach football and cricket. Further along, a boombox blasts as the smell of fresh fish wafts across the shoreline.
For years, this was the scene at the Hellshire Beach in Portmore, St Catherine, on a public holiday or weekend when Jamaicans and visitors alike would flock to one of the island’s most popular beaches. Today, however, parents no longer bring their children. The horses, along with most of the beachline, have long disappeared and the few visitors who come to Aunt Merl’s or Prendy’s on the Beach – two of the few remaining seafood restaurants left standing – are confined to the benches inside.
The beachfront has been swallowed by the surging tides, a result of decades of climate change and mismanagement.
“The recreational areas are totally gone so the sea is now right at the steps of the business places,” says Gladstone White, director of the Half Moon Bay Fishermen’s Co-operative, which has been lobbying for funding for infrastructure work to stabilize sections of the beach.
While island nations like Jamaica contribute a tiny fraction of the greenhouse gas emissions that are heating the planet, they are poised to suffer the worst consequences of the climate crisis. Coasts play a critical role in the economies of many Caribbean nations, whose population centers are close to the shore and who rely heavily on their ports and on tourists attracted to their picturesque waters. But beaches throughout the Caribbean are eroding as a result of rising sea levels and dangerous storms resulting from climate change. And many island nations lack the funding to invest in the infrastructure and innovation necessary to combat the changes – a situation made worse by the Covid crisis.
While Jamaica has a mixed record on environmental protection, the country is part of a coalition of small island nations that has been instrumental in lobbying for global climate action, and recently became the first Caribbean nation to increase the ambitiousness of its plan under the Paris climate agreement to reduce its carbon emissions.
But the US is set to withdraw from the agreement on 4 November, imperiling the treaty’s goal of limiting global heating to “well below” 2C, along with prospects for global action sufficient to ward off increased risk to the people and lands of the Caribbean.
Hellshire Beach, where the marine ecosystem is rapidly eroding, offers insight into what’s at stake for many Caribbean communities. Intensified storm activity and increased water temperatures are helping destroy offshore coral reefs that otherwise buffer the shoreline from pounding waves. The problems are compounded by unregulated commercial development and waste treatment, along with the removal of sand dunes and other vegetation. A landmark report published in 2012 found that Hellshire had lost up to 120 meters of shoreline in four decades.
When the scope of Hellshire’s destruction became clear, the government seemed ready to act quickly and decisively. A master plan to rehabilitate the beach was created – but then dashed in 2016 when the People’s National party (PNP) was swept from power. Since then, budding initiatives meant to invest in the beach have been consistently shut down, often without explanation.Advertisement
Jamaica’s economic difficulties will thwart any short-term action to save the beach. The coronavirus has served a major blow to tourism and remittances, the country’s top two sources of revenue. The post-crisis receipts from both are forecast to fall to just around half the US$5.4bn of value they represented before the pandemic, with remittances expected to decline by 17% and tourism by 68%.
Jamaica’s National Environment and Planning Agency says that while rehabilitation efforts have been derailed by the economic impact of Covid-19, they will be picked up next year. But despite Nepa’s reassurances, a tourism official told the Guardian that the Hellshire master plan has been shelved indefinitely.
White, director of the fishermen’s co-operative, says the decision to scrap the master plan will hit members “big time”.
“Thing are so bad that fishermen are finding it difficult to find places to dock their boats,” he said.
Prendy’s on the Beach was once arguably the biggest and most popular seafood restaurant on Hellshire. Now that the beach has disappeared, so too have many of its customers – a situation exacerbated by government-imposed Covid-19 restrictions on public gatherings.
“I have to be creative,” says Donnete “Prendy” Prendergast, who has been operating her restaurant at Hellshire for more than 20 years. “So I do family packages for people who still come out even if they can’t get to swim. But honestly, not being able to swim takes away from the Hellshire experience, because they come here not just to eat but to have some recreation.”
Jamaica has long sent mixed signals on its commitment to environmental protection. Environmentalists recently protested against the government’s decision to allow bauxite mining in an area that supplies drinking water to the parishes of Trelawny, St Elizabeth and St Ann. The government also met with outcry over its decision to sell off fertile land to developers to build a new city, despite the fact that just a fraction of Jamaica’s land is available for farming.
And environmentalists, archaeologists and residents have been united in their opposition to the construction of a floating pier for cruise ships in Port Royal, arguing that the fragile ecosystem is in danger. Despite this, the pier opened last year to much fanfare but generated little economic spinoff for locals.
For her part, Prendergast would be content with the government showing its commitment to addressing climate change by taking one small step towards resolving beach erosion at Hellshire.
“I think the authorities need to really give Hellshire some love because it is really a beautiful place and what we offer is really unique because you can’t go get our festivals anywhere else,” she says, referring to the cornmeal-based Jamaican fried dough sold on the beach.
But time is running out for the Hellshire Fishing Village beach and its natural and manmade allures. Soon, the forces of nature, along with local and global inaction, will make it, and many more pristine beaches in the region, no more than a distant memory – a faded photograph in an old scrapbook.
Ice sheets in Greenland and Antarctica whose melting rates are rapidly increasing have raised the global sea level by 1.8cm since the 1990s, and are matching the Intergovernmental Panel on Climate Change’s worst-case climate warming scenarios.
According to a new study from the University of Leeds and the Danish Meteorological Institute, if these rates continue, the ice sheets are expected to raise sea levels by a further 17cm and expose an additional 16 million people to annual coastal flooding by the end of the century.
Since the ice sheets were first monitored by satellite in the 1990s, melting from Antarctica has pushed global sea levels up by 7.2mm, while Greenland has contributed 10.6mm. And the latest measurements show that the world’s oceans are now rising by 4mm each year.
“Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and atmosphere, the rate at which they are melting has accelerated faster than we could have imagined,” said Dr. Tom Slater, lead author of the study and climate researcher at the Centre for Polar Observation and Modelling at the University of Leeds.
“The melting is overtaking the climate models we use to guide us, and we are in danger of being unprepared for the risks posed by sea level rise.”
The results are published today in a study in the journal Nature Climate Change. It compares the latest results from satellite surveys from the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE) with calculations from climate models. The authors warn that the ice sheets are losing ice at a rate predicted by the worst-case climate warming scenarios in the last large IPCC report.
Dr. Anna Hogg, study co-author and climate researcher in the School of Earth and Environment at Leeds, said: “If ice sheet losses continue to track our worst-case climate warming scenarios we should expect an additional 17cm of sea level rise from the ice sheets alone. That’s enough to double the frequency of storm-surge flooding in many of the world’s largest coastal cities.”
So far, global sea levels have increased in the most part through a mechanism called thermal expansion, which means that volume of seawater expands as it gets warmer. But in the last five years, ice melt from the ice sheets and mountain glaciers has overtaken global warming as the main cause of rising sea levels.
Dr. Ruth Mottram, study co-author and climate researcher at the Danish Meteorological Institute, said: “It is not only Antarctica and Greenland that are causing the water to rise. In recent years, thousands of smaller glaciers have begun to melt or disappear altogether, as we saw with the glacier Ok in Iceland, which was declared “dead” in 2014. This means that melting of ice has now taken over as the main contributor of sea level rise. ”
The study, “Ice-sheet losses track high-end sea-level rise projections,” is published today (31 August) in Nature Climate Change.
Years before Bear Grylls got meme’d for drinking his own urine, Kevin Costner did it aboard a trimaran as the nameless Mariner in 1995’s Waterworld. The film received mixed reviews and almost failed to recover its nearly $200 million budget (the largest of any movie ever made, at the time) at the box office.
Despite lackluster ticket sales, however, it found its place in the memories of moviegoers and is still remembered (and occasionally celebrated) 25 years later.
Perhaps that’s because it so perfectly encapsulates, like so much dirt in a jar, the time in which it was made. The ’90s were the peak of pop environmentalism, and Waterworld offered a possible vision of what might await us at the far end of climate change, when the ice caps have melted and the seas have claimed the Earth.
The only problem is, it’s super wrong!
The post-apocalyptic survivors of Waterworld populate an endless global ocean, living on floating cities called atolls and telling stories of fabled remnants of dry land. The notion of land is so precious, and the water so ubiquitous, that dirt is valued as currency.
The question, then, is how much water is locked inside ice caps and glaciers? And how would the world be changed if it all melted and joined the world’s oceans?
WATER DISPLACEMENT WOULD CHANGE THE EARTH’S ROTATION
The rotation speed of the Earth changes over time as a natural consequence of lunar pressure. That the Earth rotates at all is a leftover effect of the initial angular momentum of the solar system forming, and the planetary collision that resulted in the Moon.
The Sun and all its planets were, collectively, a vast top, set to spinning, and which still hasn’t stopped. That’s great news for us. The rotation of the Earth spreads energy from the Sun over the whole of the planet, rather than concentrating it on one side, as it would if the planet didn’t spin.
The difference in the rotational period from any given year to the next is nearly negligible, but it adds up. The length of a day in the Precambrian period was only 21 hours. The lengthening of the day is partially a result of lunar pressure, but is also hypothesized to have been impacted by a sudden change in global temperatures.
The rotation of the planet would also be impacted by the continued melting of ice caps and glaciers. One factor of a body’s rotation is the distribution of mass. A body with centralized mass spins more quickly than one with its mass spread out.
With ice concentrated at the poles, that mass is held closely to the center of the Earth’s axis. As it melts, and that mass is distributed across the world’s oceans, the world will spin more slowly. While the change would be measured in milliseconds, the change in global temperature might have a significant impact in diurnal cycles, particularly when extrapolated over long time periods.
CHANGING CURRENTS AND OCEAN SALINITY
While the rising tides will most directly impact humanity by submerging large population centers (more on that later), perhaps the largest global impact of melting ice is the way it would change the world’s oceans.
The most immediately obvious impact is a change to overall ocean salinity. On the surface, this isn’t a complex problem to wrap one’s mind around. The introduction of a large amount of fresh water to a salinated environment results in the desalinization of that environment. In short, melt a bunch of freshwater ice into the oceans, and they become less salty.
This could have a drastic impact on the species that live in the ocean as that environment changes. But it isn’t that simple. Much like the rest of the world, the oceans have an overall climate that is distinct from local phenomena.
If all the world’s ice melted into the oceans, it wouldn’t distribute evenly. Instead, local areas would be most heavily impacted by the influx of fresh water. Those areas would then go on to impact neighboring areas in a global domino effect.
The world’s oceans aren’t static things; they move and flow, like the wind, based on temperature, salinity, density, and subsurface geography. The flow and exchange of water across the globe is an integral part of the health of oceanic environments.
A drastic change in salinity and temperature could change the way global waters interact in ways we don’t fully understand.
The impact of a global ice melt could be sufficient to arrest some ocean currents entirely, eliminating the exchange of nutrients and oxygen in some parts of the ocean and further changing the global climate by reducing temperature circulation.
Take all of the lakes, rivers, and streams, all of the rain you’ve ever seen, every bit of water that ever came out of your tap or went down your drain. Take all of the fresh water you’ve encountered in your life and extrapolate that throughout the rest of the world. Then multiply it by 70 and you’ve got an idea of the ice. Of course, the water you experience in your day-to-day is recycled. It isn’t all different water. Still, there’s a lot of ice in the world.
If you took the world’s ice and pressed it into cubes a mile on each side, you’d need almost six million of them to trap it all.
If you lined those cubes up between the Earth and the Moon, you could build a road a mile wide with only 4 percent of them. To use them all, that road would need to be 24 miles wide. You could circle the globe with that ice 230 times and still have some left over.
All of which is to say, the world has a lot of ice. So much ice it boggles the mind. But it’s nothing compared to the total water on Earth.
All of that ice, all of the groundwater, and all of the fresh water we use to survive accounts for only 2.5 percent of the water on Earth. Almost all the rest of it is in the oceans.
If all of the ice melted, it would certainly raise sea levels, but not as much as you might think. Some of the ice is already in the ocean. The weight of that ice displaces the same amount of water it would displace were it to melt and intermix.
This is an experiment you can confirm at home by watching ice cubes melt in a glass of water. There’s zero net change in water levels there.
The real trouble is landlocked ice. Were it to melt, that water would add to the world’s oceans and cause levels to rise.
Current estimates indicate that global sea levels would rise between 60 and 70 meters (approximately 197 to 230 feet) if every glacier and ice sheet melted, a far cry from the 25,000 feet of Waterworld. Still, it’s also important to note that as temperatures rise, water expands and takes up more space.
Even if we take the extreme end of that scale, roughly 230 feet, how would it reshape the world’s landmasses?
Jeffrey Linn, a Seattle-based cartographer, has created a series of maps looking at different locales after 200 feet of sea level rise. What’s clear in looking at these maps is that land masses still exist. The continents won’t be covered over. But that doesn’t mean rising oceans won’t wreak havoc on global populations.
It’s likely, if we don’t combat climate change in a serious way, that large swaths of the world’s water ice will melt, change the behavior of the oceans, and swallow coastal lands. Dry land won’t be fabled or difficult to find, and the post-climate-change world won’t look much like Waterworld at all. But it won’t look like home, either.
Scientists boarding the D/V JOIDES Resolution off New Jersey in 1993. The sea level in an ice-free world would be 66 meters (216.5 feet) higher than now — shoulder-high to the Statue of Liberty. Credit: Kenneth G. Miller, James V. Browning, and Gregory S. Mountain.
Surprising glacial and nearly ice-free periods in last 66 million years.
New research by Rutgers scientists reaffirms that modern sea-level rise is linked to human activities and not to changes in Earth’s orbit.
Surprisingly, the Earth had nearly ice-free conditions with carbon dioxide levels not much higher than today and had glacial periods in times previously believed to be ice-free over the last 66 million years, according to a paper published in the journal Science Advances.
“Our team showed that the Earth’s history of glaciation was more complex than previously thought,” said lead author Kenneth G. Miller, a Distinguished Professor in the Department of Earth and Planetary Sciences in the School of Arts and Sciences at Rutgers University-New Brunswick. “Although carbon dioxide levels had an important influence on ice-free periods, minor variations in the Earth’s orbit were the dominant factor in terms of ice volume and sea-level changes — until modern times.”
Sea-level rise, which has accelerated in recent decades, threatens to permanently inundate densely populated coastal cities and communities, other low-lying lands and costly infrastructure by 2100. It also poses a grave threat to many ecosystems and economies.
The paper reconstructed the history of sea levels and glaciation since the age of the dinosaurs ended. Scientists compared estimates of the global average sea level, based on deep-sea geochemistry data, with continental margin records. Continental margins, which include the relatively shallow ocean waters over a continental shelf, can extend hundreds of miles from the coast.
The study showed that periods of nearly ice-free conditions, such as 17 million to 13 million years ago, occurred when the concentration of atmospheric carbon dioxide — a key greenhouse gas driving climate change — was not much higher than today. However, glacial periods occurred when the Earth was previously thought to be ice-free, such as from 48 million to 34 million years ago.
“We demonstrate that although atmospheric carbon dioxide had an important influence on ice-free periods on Earth, ice volume and sea-level changes prior to human influences were linked primarily to minor variations in the Earth’s orbit and distance from the sun,” Miller said.
The largest sea-level decline took place during the last glacial period about 20,000 years ago, when the water level dropped by about 400 feet. That was followed by a foot per decade rise in sea level — a rapid pace that slowed from 10,000 to 2,000 years ago. Sea-level rise was then at a standstill until around 1900, when rates began rising as human activities began influencing the climate.
Future work reconstructing the history of sea-level changes before 48 million years ago is needed to determine the times when the Earth was entirely ice-free, the role of atmospheric carbon dioxide in glaciation and the cause of the natural fall in atmospheric carbon dioxide before humans.
Reference: 15 May 2020, Science Advances.
Rutgers coauthors include Professor James V. Browning, doctoral student W. John Schmelz and professors Robert E. Kopp, Gregory S. Mountain and James D. Wright, the senior author of the study.