Tag Archives: Level

The effects of sea-level rise on communities are complex and unpredictable, says a new study

Climate change stands poised to melt the planet’s ice caps and raise sea levels worldwide, with dramatic effects for human society. But these effects won’t be felt all at once, a new study suggests.

Image credits Makoto Seimori.

The research, led by the University of Exeter in partnership with Cornwall Archaeological Unit, Cardiff University and 14 other institutes, focused on the Isles of Scilly, a group of islands of the UK’s south-west coast. The 140 islands of today are the remnants of a single large island which was gobbled up by the seas less than 1,000 years ago, the team reports. But the changes in land area and the shifts in human cultures associated with them took place at variable rates, they add, and were often ‘out of step’ with the average rate of sea-level rise.

Such findings showcase that the effects of rising seas are more complex and unpredictable than we assume, and will be much further reaching than simply forcing coastal communities to relocate.

Rising seas flood all boats

“When we’re thinking about future sea-level rise, we need to consider the complexity of the systems involved, in terms of both the physical geography and the human response” said lead author Dr. Robert Barnett, of the University of Exeter. “The speed at which land disappears is not only a function of sea-level rise, it depends on specific local geography, landforms, and geology.”

“Human responses are likely to be equally localized. For example, communities may have powerful reasons for refusing to abandon a particular place.”

The team studied the process through which the old island turned into the current cluster of 140 islands, which overall lasted some 12,000 years. They first developed a sea-level curve for the Isles over this time (a chart that shows sea level over time). Then, the team analyzed how these changes influenced the landscape, vegetation, and human populations from archaeological evidence as well as samples of pollen and charcoal collected by the Lyonesse Project (2009 to 2013).

The findings suggest that between 4,000 and 5,000 years ago, the island was rapidly becoming submerged. The inhabitants were seemingly trying to adapt to the changes in their landscape rather than abandoning the area altogether. Around 4,400 years ago, during the Bronze Age, the island had a permanent population that showed “a significant acceleration of activity”.

Land losses during this time were quite quick despite sea levels rising quite slowly, because a large part of Scilly at this point was relatively flat and close to sea level. According to the team, land here was being lost at a rate of around 10,000 sq. meters per year (a 100 by 100 meter square), roughly equivalent to a large rugby stadium. Exactly why these early inhabitants weren’t scared by higher seas is unclear; however, the team believes that they created more opportunities for fishing, the collection of shellfish, or the hunting of marine bird species. It’s possible that much of this lost land developed into intertidal habitats (exposed at low tide and submerged at high tide), which were still useful and traversable to coastal communities.

After around 4,000 years ago, the island was progressively submerged, even during times with lower rates of sea-level rise (around 1 mm per year).

“It is clear that rapid coastal change can happen even during relatively small and gradual sea-level rise,” said Dr. Barnett.”The current rate of mean global sea-level rise (around 3.6 mm per year) is already far greater than the local rate at the Isles of Scilly (1 to 2 mm per year) that caused widespread coastal reorganization between 5,000 and 4,000 years ago.”

“It is even more important to consider the human responses to these physical changes, which may be unpredictable. As can be seen today across island nations, cultural practices define the response of coastal communities, which can result in polarised agenda, such as the planned relocation programs in Fiji versus the climate-migration resistance seen in Tuvalu.”

Sea level rise led to new marine resources becoming available for communities on the island of Scilly, but the team believes it is “unlikely” that this mechanism will prove enough to support today’s communities as they become affected or displaced by rising sea levels.

“More certain though, is that societal and cultural perspectives from coastal populations will be critical for responding successfully to future climate change,” says Dr. Barnett.

The study “Nonlinear landscape and cultural response to sea-level rise,” has been published in the journal Science Advances.

We could see up to 1.3m of sea-level rise by 2100 if we don’t take action now

A new study says we should be expecting an average sea-level rise in excess of 1 meter by 2100 and 5 meters by 2300 if we don’t meet current targets for the reduction of greenhouse gas emissions.

Image via Pixabay.

The analysis used projections compiled by over 100 international experts to estimate changes in sea levels under low- and high-emission scenarios, the team explains, in order to help policymakers have a better understanding of “the state of the science” on this threat.

The waters are coming

“The complexity of sea-level projections, and the sheer amount of relevant scientific publications, make it difficult for policymakers to get an overview of the state of the science,” says Professor Benjamin Horton, Acting Chair of Nanyang Technological University, Singapore (NTU Singapore) Asian School of the Environment, who led the survey.

“To obtain this overview, it is useful to survey leading experts on the expected sea-level rise, which provides a broader picture of future scenarios and informs policymakers so they can prepare necessary measures.”

The most optimistic scenario analyzed in this paper considered that global warming would only increase temperatures by 2 degrees Celsius above pre-industrial levels, which would translate to a rise of 0.5 meters (roughly 2 feet) by 2100, and 0.5 to 2 meters by 2300. The high-emission scenario would involve 4.5 degrees Celsius of warming and would cause between 0.6 to 1.3 meters (2 to 4 feet) sea rise by 2100, and 1.7 to 5.6 meters by 2300.

These estimations exceed those of the International Panel on Climate Change (IPCC), who set the current targets under the Paris Agreement. Researchers from The University of Hong Kong, Maynooth University (Ireland), Durham University (UK), Rowan University (U.S.), Tufts University (U.S.), and the Potsdam Institute for Climate Impact Research (Germany) took part in this study. They were chosen as they are some of the most active publishers or scientific studies on the topic (they all had at least six published papers pertaining to sea-level rise since 2014).

The large difference in sea level rise seen in this paper “provides a great deal of hope for the future, as well as a strong motivation to act now to avoid the more severe impacts of rising sea levels,” according to Dr. Andra Garner, Assistant Professor of Environmental Science at Rowan University and co-author of the study.

Still, the findings also underscore just how important it is for policy to be set in place in order to limit emissions and sea-level rise. How bad the outcome is depends entirely on how we act, and the decisions we make right now.

However, despite the sheer wealth of expertise that went into the study, there are still uncertainties. The team points to the Greenland and Antarctic Ice Sheets as the largest unknowns, as their behavior can have dramatic effects on how sea levels evolve in the future. Both of these ice sheets are key reference points for climate change and increases in sea levels, as they hold important quantities of water — and they’re both melting at much higher rates than they would naturally.

Yet, not all is lost. Climate systems have a great deal of inertia to them (as do all systems working on such scales) but taking proactive measures to limit greenhouse gas emissions would still have a significant effect.

So while the worst-case scenario definitely does seem bleak, it’s in no way out of our hands. We can choose to make things better, to limit the impact we have on the planet and the repercussions that will have on our society in the future.

The paper “Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey,” has been published in the journal Climate and Atmospheric Science.

Sea level rise could displace 13 million Americans by 2100

New research from the University of Southern California (USC) looks at how rising sea levels will affect population dynamics in the US. By their estimates, 13 million people will be displaced by 2100, placing extreme strain on several cities throughout the country.

Image credits NASA.

Global warming is driving sea-levels up through two main mechanisms: increased water inflow from melting ice sheets and glaciers, and the thermal expansion of warming water. Human populations tend to mostly gravitate around coasts and waterways and, as such, it’s estimated that sea-level rise will destroy hundreds of thousands of homes in just a few decades. Current estimates place sea level increase by the end of the century at a 6-foot mark, which would redraw the coastlines of Florida, North Carolina, Massachusetts, Louisiana, and New Orleans.

Which begs the question — where will the displaced go to?

Water damage

“Sea level rise will affect every county in the US, including inland areas,” says Bistra Dilkina, an Assistant Professor of Computer Science from the USC’s Center for AI for Society.

“We hope this research will empower urban planners and local decision-makers to prepare to accept populations displaced by sea-level rise. Our findings indicate that everybody should care about sea-level rise, whether they live on the coast or not. This is a global impact issue”.

In the aftermath of Hurricane Harvey (2017), displaced residents from the coast of Texas flocked inland. The team explains that this event showcases what could happen, on a much wider scale, within a few decades. Some 13 million people could be forced to relocate due to rising sea levels by 2100 in the US alone, they found, which would place an enormous strain on the population centers they migrate to. The strain of this environmental disaster will thus ripple throughout the country, not just on the affected coastlines, as people move inland. Among the effects, the team lists more competition for jobs, increased housing prices, and huge pressure on infrastructure and social systems.

The team is the first to use machine learning to project future migration patterns resulting from sea-level change. According to their findings, land-locked cities such as Atlanta, Houston, Dallas, Denver, and Las Vegas will see the highest number of refugees. Suburban areas in the Midwest are also likely to see a disproportionately large number of refugees relative to their current local populations.

For the study, the team took existing sea-level projections and combined them with population data and their projections until the end of the century. Migration pattern data recorded after Hurricane Katrina and Hurricane Rita was used to train machine learning models to predict where people would relocate in the simulated world.

“We talk about rising sea levels, but the effects go much further than those directly affected on the coasts,” said Caleb Robinson, a visiting doctoral researcher from Georgia Tech and the study’s first author.

“We wanted to look not only at who would be displaced, but also where they would go.”

Inland areas immediately adjacent to the coast bore the brunt of the migration, the team found, as did urban areas in the southeastern US. However, their model showed that more migrants would flock to Houston or Dallas than previous studies on the topic — these identified Austin as the top destination for climate refugees from the southeastern coast.

The study suggests that climate-change-induced migrations won’t necessarily follow previous patterns of movement. The authors hope that their findings will help policymakers and city planners reinforce infrastructure to ensure that the influx of refugees will have a positive impact on local economies and communities.

“When migration occurs naturally, it is a great engine for economic activity and growth,” said co-author Juan Moreno Cruz, an economist and professor at the University of Waterloo. “But when migration is forced upon people, productivity falls and human and social capital are lost as communities are broken apart.”

“Understanding these migration decisions helps economies and policy makers prepare for what is to come and do as much as possible to make the influx of migration a positive experience that generates positive outcomes.”

The paper “Modeling migration patterns in the USA under sea level rise” has been published in the journal PLOS ONE.

Greenland is losing ice seven times faster than in the 1990s

Greenland’s rate of ice loss is increasing faster than expected, a new metastudy reports.

The increased influx of water from Greenland’s ice sheet puts us on track for sea-level rise consistent with the Intergovernmental Panel on Climate Change’s (IPCC) high-end climate warming scenario. Projections for this scenario estimate that coastal flooding will displace 400 million people by 2100.

Image credits Jean-Christophe Andre.

The study is a collaboration between 96 polar scientists from 50 international organizations — The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team — and takes the most complete look at Greenland’s long-term ice loss to date. It combined 26 separate surveys to track changes in the ice mass of Greenland between 1992 and 2018. Data from 11 different satellite missions was used to measure the ice sheet’s changing volume, flow, and mass.

Melting quick

“On current trends, Greenland ice melting will cause 100 million people to be flooded each year [by 2100], so 400 million in total due to all sea level rise,” says Professor Andrew Shepherd at the University of Leeds, one of the study’s co-lead authors.

Melt rate in Greenland has risen from 33 billion tons, on average, per year in the 1990s to 254 billion tons per year over the last decade. In total, the island lost roughly 3.8 trillion tons of ice since 1992.

The IPCC mid-warming scenario set out in 2013 estimated 60 centimeters of sea-level rise by 2100, with associated coastal flooding displacing an estimated 360 million people. The rates of melt reported on in this study push those estimates by an additional 5 to 12 cm — consistent with the projection for the high-warming climate scenario.

“As a rule of thumb, for every centimeter rise in global sea level another six million people are exposed to coastal flooding around the planet,” Professor Shepherd explains.

The report shows that half of the ice losses recorded between 1992 and today have been caused by higher average temperatures, which promoted surface melting. The rest, around 48% of the total ice mass lost, was caused by increased glacier flow into the ocean due to warmer waters. Melting peaked 335 billion tonnes per year in 2011 but has since decreased to 238 billion tonnes per year “as atmospheric circulation favored cooler conditions”.


The team notes that this lower rate is still seven times higher than that in the 1990s, and that the dataset didn’t include all of 2019. Higher rates of melt expected in the summer could push Greenland to see record quantities of ice loss.

“Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise” said Erik Ivins at NASA’s Jet Propulsion Laboratory in California, and co-lead author of the study.

Researchers from the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA) also took part in the IMBIE report.

The paper “Mass balance of the Greenland Ice Sheet from 1992 to 2018” has been published in the journal Nature.

Sea level rise by 2300 is unavoidable, despite the Paris agreement

We’re set on the path of rising sea levels, even if the pledges made for the Paris climate agreement are met and global temperatures stabilize, a new paper reports.

Image via Pixabay.

The Paris agreement on climate change mitigation was adopted in December 2015 and aims to limit the rise of global average temperatures to a maximum of 2°C compared to pre-industrial levels. The ideal scenario under the agreement would be to limit this figure to 1.5°C, and the countries that signed into the agreement are expected to make efforts towards this goal.

While a successful Paris agreement would do wonders for our efforts against climate heating and environmental degradation, we’re already set for rising sea levels around the world by 2300, a new study reports.

We’re already there

“Even if we were to meet these initial goals of the Paris agreement, the sea level commitment from global warming will be significant,” said Peter Clark, an Oregon State University climate scientist and a co-author of the study.

“When we pump more carbon into the atmosphere, the increase in temperature is almost immediate. But sea level rise takes a lot longer to respond to that warming. If you take an ice cube out of the freezer and put it on the sidewalk, it takes some time to melt. The bigger the ice cube, the longer it takes to melt.”

The authors say this is the first effort to quantify how sea levels will rise from carbon emissions (both past and future) released since the agreement was signed. In the first 15 years following the agreement, they report, will cause a rise of roughly 20 centimeters (7.9 in) by 2300. The estimate does not take into account the effect of irreversible melting in parts of the Antarctic ice sheet, the team adds, which is already underway.

A one-meter rise is expected by 2300, caused by emissions dating back to the year 1750. Around 20% of that rise can be traced back to emissions released since after the Paris agreement was signed. Around half of it (so 10% of the total projected rise) is attributable to the world’s top five polluters, the team found: the United States, China, India, Russia, and the European Union

Sea level rise is a huge threat to coastal ecosystems and human communities, with the potential to affect and/or displace hundreds of millions around the world (coastal areas are the most heavily-inhabited regions on Earth). Sea level rise is mostly driven by melt from glaciers and ice sheets draining into the ocean. But these are massive structures strewn all over the world, and they each respond to climate heating in their own time, ranging from decades to millennia.

“Much of the carbon dioxide we’ve emitted into the atmosphere will stay up there for thousands of years,” said Clark, who is on the faculty of OSU’s College of Earth, Ocean, and Atmospheric Sciences.

“So our carbon emissions this century are not only committing our planet to a warmer climate, but also to higher sea levels that will also persist for thousands of years.”

The paper “Attributing long-term sea-level rise to Paris Agreement emission pledges” has been published in the journal Proceedings of the National Academy of Sciences.

Researchers have solid proof that the sea is rising — five islands have been lost so far, six more underway in the Solomon Islands

Sea level rise threatens to gulp up coasts and islands in the future; a new study shows that the future is already here in that regard.

A vista from Visale, Solomon Islands.
Image via Wikimedia.

At least five islands in the Solomon Islands chain have been completely lost to rising seas and coastal erosion. These islands have completely vanished under the surface, and the authors note at least two cases where entire human populations have had to relocate to avoid the waves.

This is the first scientific evidence that confirms anecdotal accounts from across the Pacific of the dramatic impacts of climate change on coastlines and communities.

Et tu, Atlantis?

“Using time series aerial and satellite imagery from 1947 to 2014 of 33 islands, along with historical insight from local knowledge, we have identified five vegetated reef islands that have vanished over this time period and a further six islands experiencing severe shoreline recession,” the authors write.

The five lost islands ranged in size from one to five hectares and supported dense tropical vegetation, the study explains. Some of the islands that are in the process of disappearing are inhabited. Nuatambu Island, home to 25 families, has lost more than half of its habitable area (and 11 houses) into the sea since 2011.

The findings are both surprising and worrying, as previous research had estimated that islands in the Pacific can keep pace with sea-level rise, and maybe even expand. However, the team notes that those studies focused on areas of the Pacific where sea levels rise by only 3-5 mm per year – broadly in line with the global average of 3 mm per year. The Solomon Islands have experienced a much more rapid sea level rise over the last two decades, at almost three times the global average.

This higher local rate is partly the result of natural climate variability. However, they’re a good indication of how fast sea levels will rise around the world in a warmer future. While natural variations and geological activity will affect future rates of sea level rise, if we don’t dramatically slash greenhouse emissions, what’s happening in the Solomons right now will become the new normal.

It’s not just that the sea is creeping up — it’s also slowly breaking apart the islands. The team says that rates of coastal erosion in the Solomon Islands are ‘dramatic’ and point to increased wave energy as the likely culprit. Those islands that had to contend with both higher wave energy and sea-level rise fared the worst out of all the islands in the study. Around 12 islands in a low wave-energy area showed very little change in their shorelines, while out of 21 exposed islands 5 disappeared completely and 6 showed substantial levels of erosion.

Twelve islands that were studied in a low wave energy area of Solomon Islands experienced little noticeable change in shorelines despite being exposed to similar sea-level rise. However, of the 21 islands exposed to higher wave energy, five completely disappeared and a further six islands eroded substantially.

The paper “Interactions between sea-level rise and wave exposure on reef island dynamics in the Solomon Islands” has been published in the journal Environmental Research Letters.

Greenland set to accelerate sea level change in the near future

Greenland’s contribution to sea-level rise is increasing, as climate change makes the region release meltwater into the ocean.

Image via Pixabay.

Greenland’s ice sheet is experiencing an increase in ice slab thickness at its interior regions. These ice sheets are normally porous, allowing meltwater to percolate (drain through) them, but the extra thickness makes them impermeable — so all the meltwater is draining into the ocean.

The process could see the country’s contribution to sea level rise increase by as much as 2.9 inches by 2100.

Thicc ice

“Even under moderate climate projections, ice slabs could double the size of the runoff zone by 2100,” said Mike MacFerrin, a CIRES (Cooperative Institute for Research In Environmental Sciences) and University of Colorado Boulder researcher who led the new study. “Under higher emissions scenarios, the runoff zone nearly triples in size.”

Runoff from ice slabs only amounts to a one-millimeter increase in global sea levels so far, the team explains, but that contribution will expand substantially under climate warming.

In the year 2000, Greenland’s runoff zone — the region of the ice sheet where runoff contributes to sea level rise — was roughly equivalent to the size of New Mexico. Between 2001 and 2013, it expanded by an average of two American football fields per minute, reaching roughly 65,000 sq km.

Even under a moderate emissions scenario, the team adds, it could reach the size of Colorado by 2100. That would raise sea levels by an extra 7-33 mm (one-quarter to one inch) by the same timeframe. Under a high emissions scenario, the situation looks even bleaker: the runoff zone could increase by the size of Texas, according to the new paper, contributing an extra 17-74 mm (half-inch to nearly three inches) of sea-level rise.

The runoff estimates from ice slabs are in addition to other sources of sea-level rise from Greenland, such as calving icebergs.

The team explains that Greenland’s ice sheets are made of layers with different textures. Fresh snow that falls each winter either melts into surface lakes or builds-up and helps compact older snow into glacial ice. Snow that partially melts over summer later re-freezes into thin ice “lenses” between 2 to 5 mm (one or two inches) thick within the compacted snow.

Normally, meltwater can percolate through and around ice lenses, refreezing in place without running off to sea. As mean temperatures over the Arctic increase and melting events become more frequent and extreme, however, these ice lenses solidify into slabs between 1 and 16-meter (3- to 50-foot) thick. These slabs block water from flowing through, which ends up flowing downhill into the ocean.

Climate warming is also increasing the quantity of meltwater in Greenland. In July of 2012, snow and ice melted from 97% of Greenland’s ice sheet surface, which the team says has never before been seen the 33-year-long satellite record. This spring, which was particularly warm and sunny in Greenland, resulted in a record-setting 80 billion tons of Greenland ice melted.

“As the climate continues to warm, these ice slabs will continue to grow and enhance other meltwater feedbacks,” said Mahsa Moussavi, a coauthor on the paper. “It’s a snowball effect: more melting creates more ice slabs, which create more melting, which creates again more ice slabs.”

All in all, this process will fundamentally alter the ice sheet’s equilibrium. The team warns that we need to understand Arctic feedbacks like this one because they show just how much, and how quickly, a warming climate can change Earth’s most vulnerable regions.

“Humans have a choice about which way this goes,” MacFerrin said.

The paper “Rapid expansion of Greenland’s low-permeability ice slabs” has been published in the journal Nature.


Our emissions could melt all the ice in Greenland by the year 3000 — and raise sea levels by 24 ft

Greenland may actually be green by the end of the millennium if greenhouse emissions continue unabated.


Image credits Marcel Prueske.

New research shows that, if greenhouse gas emissions continue on their current trajectory, Greenland could lose 4.5% of its ice by the end of the century, and all of it by the year 3000. That 4.5% loss of ice is equivalent to roughly 13 inches of sea level rise, the team explains.

Actually Green land

“How Greenland will look in the future — in a couple of hundred years or in 1,000 years — whether there will be Greenland, or at least a Greenland similar to today, it’s up to us,” said first author Andy Aschwanden, a research associate professor at the University of Alaska Fairbanks Geophysical Institute.

Greenland houses a lot of ice — around 660,000 square miles of solid ice sheet, which contains around 8% of all the planet’s fresh water. Between 1991 and 2015, melting here has added about 0.02 inches per year to the sea level. Needless to say, we need to know how all that ice is faring and whether there’s any cause for concern. Turns out that there is.

The team used recent topography (landscape) data of Greenland’s terrain today to model how its ice sheets will evolve in the future. This data was recorded by a NASA airborne science campaign (Operation IceBridge) during which aircraft fitted with a full suite of scientific instruments scanned Greenland’s ice sheets recording its surface, the individual layers within, and the shape of the bedrock. On average, Greenland’s ice sheet is 1.6 miles thick, but there was a lot of variation.

A wide range of scenarios concerning ice loss and changes in sea level are possible based on how greenhouse gas concentrations and atmospheric conditions evolve. The team ran 500 simulations for each emission scenario using the Parallel Ice Sheet Model, developed at the Geophysical Institute, to create a picture of how Greenland’s ice would respond to different climate conditions. The model included parameters on ocean and atmospheric conditions as well as ice geometry, flow, and thickness.

Under a business as usual scenario, we could see around 24 feet to global sea level rise by the year 3000 due to melting in Greenland alone — which would put much of San Francisco, Los Angeles, New Orleans and other cities under water. However, if we do manage to slash greenhouse gas emissions significantly, the prospects improve. Reduced emission scenarios showed between 8% to 25% melting of Greenland’s ice, which would lead to approximately 6.5 feet of sea level rise

Projections for both the end of the century and 2200 tell a similar story. A wide range of outcomes are possible, including saving the ice sheet, but it all depends on emission levels, the team explains.

The team explains that modeling ice sheet behavior is tricky because ice loss is primarily driven by the retreat of outlet glaciers. These are the glaciers at the margin of the ice sheets, and they ‘drain’ ice from deeper in the sheets through through-like structures in the bedrock. This study was the first to include these outlet glaciers in its modeling and found that their discharge could contribute as much as 45% of the total mass of ice loss in Greenland by 2200. Outlet glaciers come into contact with water, the team explains, which makes ice melt much faster than air. The more ice that comes into contact with water, the faster the rate of melting — which creates a feedback loop that dramatically affects the ice sheet’s stability.

Previous research lacked data as comprehensive as that recorded by IceBridge, so it couldn’t simulate the ice sheets’ evolution in such detail.

“Ice is in very remote locations,” says Mark Fahnestock, a researcher at the University of Alaska Fairbanks Geophysical Institute and paper co-author. “You can go there and make localized measurements. But the view from space and the view from airborne campaigns, like IceBridge, has just fundamentally transformed our ability to make a model to mimic those changes.”

“What we know from the last two decades of just watching Greenland is not because we were geniuses and figured it out, but because we just saw it happen,” he adds. As for what we will see in the future, “it depends on what we are going to do next.”

The paper “Contribution of the Greenland Ice Sheet to sea level over the next millennium” has been published in the journal Science Advances.


Sea level change isn’t constant across the East Coast — because of long-past glaciers

A new study explains why different areas along the U.S. East Coast see significantly more sea level change than others.


Image credits Dimitris Vetsikas.

Seas and oceans across the globe are creeping ever so slowly upwards as climate change warms them up and melts glaciers big and small. However, local sea levels aren’t (surprisingly) the same everywhere — and this holds true for the U.S. East Coast as well. A new study published by researchers from the Woods Hole Oceanographic Institution (WHOI) comes to explain why.

Been under a lot of pressure lately

Over the last century, coastal communities near Cape Hatteras (North Carolina) and the Chesapeake Bay (Virginia) have seen about a foot and a half of sea level rise.  New York City and Miami, in contrast, have only seen roughly two-thirds of that rise (i.e. one foot) over the same period. Farther north in Portland, Maine, for example, sea levels only rose only about half a foot.

Which is weird, right? I mean, all the Earth’s oceans are linked together so, their water should be level, right? Not if you’re on a period of post-glacial rebound, says lead author Chris Piecuch.

Vast areas of land in the Northern Hemisphere, including Canada and parts of the Northeast U.S, were covered in massive glaciers during the last Ice Age, he explains. This effectively squashed the lands, pushing them down into the mantle (the crust is essentially a jigsaw puzzle of solid pieces floating on molten rock — see here). These ice sheets peaked in size and mass during the Last Glacial Maximum some 26,500 years ago, and then started melting to the state we see today. As they did so, the pressure they exerted on the ground also disappeared — and these areas started to rebound. Neighboring lands, meanwhile, started sinking, creating sort of a seesaw effect.

That effect continues to this day, Piecuch explains.

For the study, Piecuch and his team gathered tidal gauge measurements of sea levels in areas such as Norfolk Naval Station in Virginia and the Outer Banks in North Carolina. They also drew on GPS satellite data to see how much local landmasses had moved up and down over time, and looked to fossils recovered from salt marshes (which are a good indicator of past coastal sea levels). They combined all of this observational data with complex geophysical models to produce a more complete view of sea level changes since 1900 than ever before.

Post-glacial rebound, they found, accounted for most of the variation in sea level rise along the East Coast. Interestingly, however, when that factor was removed from the dataset, the team found that “sea level trends increased steadily from Maine all the way down to Florida.”

“The cause for that could involve more recent melting of glaciers and ice sheets, groundwater extraction and damming over the last century,” Piecuch says. “Those effects move ice and water mass around at Earth’s surface, and can impact the planet’s crust, gravity field and sea level.”

“Post-glacial rebound is definitely the most important process causing spatial differences in sea level rise on the U.S. East Coast over the last century. And since that process plays out over millennia, we’re confident projecting its influence centuries into the future. But regarding the mass redistribution piece of the puzzle, we’re less certain how that’s going to evolve into the future, which makes it much more difficult to predict sea level rise and its impact on coastal communities.”

The paper “Origin of spatial variation in US East Coast sea-level trends during 1900–2017” has been published in the journal Nature.


Rising seas might mean more coral reef islands — if we don’t murder all the corals

There might be a silver lining to sea level rise — emphasis on ‘might’.


Coral reef rim islands, Huvadhoo Atoll, Republic of Maldives.
Image credits Prof. Paul Kench.

New research proposes that rising sea levels may help the long-term formation of coral reef islands, such as the Maldives. However, all the other bits of climate change may destroy any benefits it brings.

Climate change, island change

“Coral reef islands are typically believed to be highly vulnerable to rising sea levels. This is a major concern for coral reef island nations, in which reef islands provide the only habitable land,” says lead author Dr. Holly East of the Department of Geography and Environmental Sciences at Northumbria University, Newcastle.

Coral reef islands aren’t very keen on altitude; typically, they’re less than three meters (about 10 feet) above the water’s surface. This obviously makes them very vulnerable to rising sea levels. However, the same high seas might’ve also created the islands, the team reports.

The researchers studied five islands in the southern Maldives. By drilling out core samples, they were able to reconstruct when and how the islands formed. They report that storms off the coast of South Africa created a series of large waves (‘high-energy wave events’) that led to the formation of the Maldives. These violent waves dislodged large chunks of pre-existent reefs and transported them onto reef platforms. This stacking of reef material created the foundations of the islands we see today.

“We have found evidence that the Maldivian rim reef islands actually formed under higher sea levels than we have at present,” Dr. East adds.

“This gives us some optimism that if climate change causes rising sea levels and increases in the magnitude of high-energy wave events in the region, it may actually create the perfect conditions to reactivate the processes that built the reef islands in the first place, rather than drowning them.”

The seas were around 0.5 meters (1.5 feet) higher than today during the islands’ formations — this allowed the waves to carry more energy. Both the higher sea level and large wave events were critical to the construction of the islands. Now, (man-made) climate change is also pushing up sea levels; the team says that projected increases in both sea level and the magnitude of large wave events could actually lead to the growth of reef islands.

For that to happen, however, you need living, healthy coral in the region’s reef communities, Dr. East stresses. And we’re murdering them pretty fast right now.

“As these islands are mostly made from coral, a healthy coral reef is vital to provide the materials for island building. However, this could be problematic as corals face a range of threats under climate change, including increasing sea surface temperatures and ocean acidity,” she says.

“If the reef is unhealthy, we could end up with the perfect building conditions but not the bricks.”

She also cautioned that “the large wave events required for reef island building may devastate island infrastructure, potentially compromising the habitability of reef islands in their current form.” Factoring in higher sea levels as well, she says that reef island nations need to “develop infrastructure with the capacity to withstand, or be adaptable to, large wave events” — a task she summarizes as being a “challenge”.

Their paper, “Coral Reef Island Initiation and Development Under Higher Than Present Sea Levels,” has been published in the journal Geophysical Research Letters.


Rising seas, rising costs: some $14 trillion worldwide per year by 2100

Sea level change won’t just displace millions from their homes — but also drain our coffers.


Image via Pixabay.

If we fail to contain climate change as per the United Nations’ 2ºC limit, we’d better be ready to cough up some dough. The change in sea level will have dramatic economic consequences, potentially costing us some $14 trillion worldwide annually by 2100, according to new research led by the UK National Oceanographic Centre (NOC).

Show me the money

“More than 600 million people live in low-elevation coastal areas, less than 10 meters above sea level,” says lead author Dr. Svetlana Jevrejeva, from the NOC. “In a warming climate, global sea level will rise due to melting of land-based glaciers and ice sheets, and from the thermal expansion of ocean waters. So, sea level rise is one of the most damaging aspects of our warming climate.”

The research stemmed from the lack of any sea level projections covering scenarios of warming below the 2°C and 1.5°C targets during the entire 21st century and beyond, the team writes. It might sound like some obscure, overly-technical tidbit of science, but such projections are actually invaluable to us today — they’re the closest thing we have to scrying the future in a crystal ball. With the added benefit that they actually work, unlike said balls.

Armed with such projections, we can make an informed decision on our actions today.

Sea Change.

Image credits S. Jevrejeva et al., 2018, Environmental Research Letters.

For the study, the team estimated the pace and consequences of sea level rise (on both a local and global level) in scenarios where warming was restricted to 1.5 ºC and 2 ºC. Then, they compared these projections to those of scenarios that assume unmitigated warming — emissions scenario Representative Concentration Pathway (RCP) 8.5.

Finally, drawing on country income groups as detailed by the World Bank (high, upper middle, lower middle, and low-income countries), the team assessed what bill these sea level changes will entail for us. These cost estimations focused mostly on costs associated with coastal areas both from a global perspective and on the level of a few individual countries, using the Dynamic Interactive Vulnerability Assessment (DIVA) framework. DIVA is a global model of coastal systems used to asses the consequences of sea-level rise on human communities and wild species based on parameters such as coastal erosion (both direct and indirect), coastal flooding (including rivers), wetland surface change, and salinity intrusion into deltas and estuaries.

“We found that with a temperature rise trajectory of 1.5°C, by 2100 the median sea level will have risen by 0.52m (1.7ft),” Dr Jevrejeva explained. “But, if the 2°C target is missed, we will see a median sea level rise of 0.86m (2.8ft), and a worst-case rise of 1.8m (5.9ft).”

“If warming is not mitigated and follows the RCP8.5 sea level rise projections, the global annual flood costs without adaptation will increase to $14 trillion per year for a median sea level rise of 0.86m, and up to $27 trillion per year for 1.8m. This would account for 2.8 per cent of global GDP in 2100.”

The team also adds that upper-middle income countries (such as China, for example) would see the largest increase in flood costs. While sea level rise will affect everyone roughly equally, richer countries will feel the effects the least — mostly due to their current infrastructure providing better protection than those of poorer countries.

Country costs.

Image credits S. Jevrejeva et al., 2018, Environmental Research Letters.

Tropical areas, however, will see extreme sea levels more often than the rest of the world. The changes will have a severe and negative effect on the economies of developing coastal nations and the habitability of low-lying coastlines.

“Small, low-lying island nations such as the Maldives will be very easily affected,” Dr Jevrejeva concludes, “and the pressures on their natural resources and environmental will become even greater. These results place further emphasis on putting even greater efforts into mitigating rising global temperatures.”

The paper “Flood damage costs under the sea level rise with warming of 1.5 °C and 2 °C” has been published in the journal Environmental Research Letters.


Half a degree (C) more global warming would leave 5 million people homeless

The seemingly inconsequential jump from 1.5 degrees to 2.0 degrees Celsius of global warming is anything but — that half of a degree would mean 5 million people across the world will need to move, or find a way to live in flooded areas.


Image credits George Hodan.

The 2015 Paris climate agreement seeks to stabilize global temperatures to less than 2 degrees Celsius above pre-industrial levels, with efforts made to ensure we never go more than 1.5 degrees Celsius above pre-industrial levels. And that sounds like a reasonable, safe goal. An international team from the Princeton, Rutgers, and Tufts Universities, alongside researchers from Climate Central and ICF International, however, wanted to find out what such a scenario would entail for people living in the most at-risk areas — coastal areas.

Still underwater

They drew on a global network of tide gauges and a framework of local sea-level projections to estimate how the frequency of storm surges and other extreme sea-level events would fare under three scenarios: global temperature increases of 1.5°, 2.0°, and 2.5°C.

Their results suggest that by 2150, the minute difference between an increase of 1.5° and 2.0°C would equate to the permanent inundation of areas that currently house 5 million people, including 60,000 who live in small island nations.

“People think the Paris Agreement is going to save us from harm from climate change, but we show that even under the best-case climate policy being considered today, many places will still have to deal with rising seas and more frequent coastal floods,” said first author DJ Rasmussen.

Unsurprisingly, the team reports that higher temperatures will make extreme sea level events much more common than they are today. Based on long-term hourly tide gauge records, they estimated current and future return periods of such events throughout the 22nd century. Under the 1.5°C scenario, this value is still expected to increase. For example, New York City is expected to see one Hurricane Sandy-like flood event every five years by the end of the 21st century under these conditions.

Extreme sea levels can be borne of high tides, storm surges, or a combination of these two — sometimes referred to as a storm tide. When whipped by hurricanes or other large storms, such events can flood into coastal areas, threatening life and property alike. A background of rising average sea levels will only compound the destructiveness and frequency of such events.

How much sea levels rise, on average, depends on how global mean surface temperatures evolve in the future. However, caution to the wise, the team notes that even if temperatures stabilize, sea levels are expected to continue to rise for centuries — because carbon dioxide lingers in the atmosphere for a long time and ice sheets will have inertia in responding to climate change.

Still, the researchers predict that by the end of the century, coastal flooding may be among the costliest impacts of climate change in some regions. Overall, a 1.5°C temperature increase by the end of the century (the best-case scenario under the Paris agreement) would equate to a roughly 1.6 feet (48 cm) mean sea level rise, and a 2.0°C increase to about 1.8 feet (56 cm). A 2.5°C increase would result in an estimated 1.9 feet (58 cm) increase, the team adds.

The paper “Extreme sea level implications of 1.5 °C, 2.0 °C, and 2.5 °C temperature stabilization targets in the 21st and 22nd centuries” has been published in the journal Environmental Research Letters.