Shrinking of ice shelves raises sea level concerns

Shrinking of ice shelves raises sea level concerns

Evidence of rapid reduction of West Antarctica’s shelf ice could have serious implications for global sea levels in a warming world.

LONDON, 29 March, 2015 – Scientists in the US report that the volume of Antarctic shelf ice is diminishing, and that there has been an 18% shrinkage in the mass of some ice floating on coastal waters over the last 18 years.

And because much of the loss has been off West Antarctica, where shelf ice helps to keep the ice sheet stable, it could mean that global sea levels will rise even faster as a result of increased glacial flow into the ocean.

The findings once again raise concern about the link between man-made emissions of greenhouse gases and the dangerous new world of global warming, climate change and sea level rise.

Fernando Paolo, a researcher at the Scripps Institution of Oceanography at the University of California, San Diego, and colleagues report in the journal Science that they used continuous radar altimetry measurements − taken from three European Space Agency satellites between 1994 and 2012 − to compose a high-resolution record of shelf ice thickness.

Declined swiftly

They found that the total volume of shelf ice – the thickness multiplied by the shelf area – around Antarctica stayed more or less the same from 1994 to 2003, but then declined very swiftly.

The ice shelves of West Antarctica lost ice during the entire period, and although East Antarctica had been gaining shelf ice, these gains ceased after 2003. Some shelves had lost 18% of their volume.

“Eighteen per cent over the course of 18 years really is a substantial change,” Paolo says. “Overall, we show not only that the total ice shelf volume is decreasing, but we see an acceleration in the last decade.”

Shelf ice is frozen sea, so when it melts, it makes no difference to sea levels. But there could be an indirect effect.

“The ice shelves buttress the flow from grounded ice into the ocean, and that flow impacts sea levels rise, so that’s a key concern from our new study,” says co-author Helen Fricker, a glaciologist at the Scripps Institution.

In climate science, one such study is never enough: such conclusions need support from other studies. But the ice volume measurements are likely to add to growing concern about West Antarctica.

“The ice shelves buttress the flow from
grounded ice into the ocean, and that
flow impacts sea levels rise”

One earlier study looked at the potential loss of ice from West Antarctica by examining the “grounding lines” of the terrestrial glaciers, and found evidence of continuous and accelerating retreat. In effect, the West Antarctic ice sheet could be approaching a point of no return, scientists reported.

And a second group used other satellite measurements to calculate that ice was being lost from the southern continent at an increasing rate – around 150 cubic kilometres a year from West Antarctica.

So the Scripps study indirectly backs up earlier findings. It calculates that most mass has been lost from ice shelves in the Amundsen and Bellingshausen seas, off the coast of West Antarctica. These account for less than 20% of the total West Antarctic ice-shelf area, but contribute more than 85% of the total ice-shelf volume loss from West Antarctica.

Slow process

Were the West Antarctic ice sheet to melt completely – a long, slow process at almost any temperatures – sea levels would rise by more than three metres worldwide.

At current rates, a couple of the ice shelves off the western coast of the continent could disappear completely within 100 years, the Scripps team says.

Although the Arctic is one of the fastest-warming places on the planet, and although this warming has been directly linked to man-made climate change, the pattern of temperature shifts in the southern hemisphere has been more ambiguous.

The Scripps team have now begun to think about possible reasons for the loss of shelf ice in the far south, and one factor might be the cycle of El Niño events – natural and periodic bubbles of Pacific ocean warmth that have waxed and waned at intervals and changed the prevailing weather patterns worldwide through history.

“We’re looking into connections between El Niño events in the tropical Pacific and changes in the Antarctic ice sheet,” Paolo says. “It’s very far apart, but we know these teleconnections exist. That may ultimately allow us to improve our models for predicting future ice loss.” – Climate News Network

Share This:

Eyes in the sky see seas rising alarmingly faster

Eyes in the sky see seas rising alarmingly faster

Scientists analysing sophisticated satellite data warn that rises in sea level more rapid than expected are increasing threats to coastal cities and food security.

LONDON, 27 March, 2015 − Satellite observations show that sea level rise may have been underestimated, and that annual rises are increasing.

A collaborative effort between maritime organisations and space agencies in measuring sea level rise has come to the conclusion that it has been increasing by 3.1 millimetres a year since 1993 – higher than previous estimates.

The evidence is growing from a number of recent studies of the ice caps that sea level rise is accelerating, posing a threat to many of the world’s largest and most wealthy cities − most of which are also important ports.

Many of these in the developing world have little or no protection against rising sea levels. Some in Europe – such as London and Rotterdam − already have flood barriers to protect areas below high tide or storm surge level, but  these will need to be replaced and raised in the next 30 years.

Delta areas in Egypt, Vietnam, Bangladesh and China – vital to each of the nation’s food supply – are already losing land to the sea.

Difficult to measure

One of the problems scientists have had in getting accurate worldwide data is that the sea does not rise evenly around the globe. This, added to the fact that in some places the land is sinking and in other places is rising, makes exact information difficult to measure from tide gauges.

Since 1991, it has been possible to measure the surface of the oceans across the entire globe by using satellite altimetry, whereby the satellite emits a signal towards the ocean’s surface and receives the reflected echo. The sea level is calculated from the round-trip time between the satellite and the sea surface and the position of the satellite along its trajectory.

While the data from tide gauges provides information about local changes relative to the land, the use of altimeter satellites enables the recording of data on a global basis.

Luciana Fenoglio-Marc, a scientist specialising in physical and satellite geodesy at the Technical University of Darmstadt, Germany, uses these and other satellite geodetic observation data in her research.

She is working with the European Space Agency and the European Organisation for the Exploitation of Meteorological Satellites, and in close consultation with the German Federal Institute of Hydrology and the Federal Maritime and Hydrographic Agency of Germany.

This lends credibility to the report that European coastal cities are not sufficiently prepared for the threats that climate change poses

The increase of around 3.1mm per year since 1993 indicates a marked rise in the average sea level when compared to previously recorded values, which show a sea level rise of between 1mm and 2mm per year in the 20th century.

In its fifth Assessment Report (AR5, 2013), the Intergovernmental Panel on Climate Change (IPCC) predicted a further increase in the global sea level of 30cm to 70cm by the end of the 21st century, based on a scenario involving a medium rate of global warming.

The report predicted that increases will not be even, but will have a greater impact on some regions than on others. The result could be coastal flooding and rising groundwater levels – an outlook that makes it essential to have a reliable data basis for dealing with the dangers this poses.

Protecting coasts from the rising seas will require considerable adaptations, particularly in such low-lying coastal regions as the North Sea coast of Germany and the many low-lying islands in the tropics.

Another aspect of the work with satellites is measuring ocean density to see how much water expansion − because of warming − is leading to sea level rise. A direct estimation of mass changes in the Mediterranean Sea show expansion to be the cause of an average sea level rise of about 2.1mm per year since 1993.

According to the IPCC, about 35% of the sea level increase between 1993 and 2010 was the result of thermal expansion, and the rest was due to melting ice and increasing run-off from land. But the latest observation shows this may not be true of the Mediterranean.

Too cautious

There is wide debate about whether the IPCC estimates of sea level rise have been too cautious, suggesting that the sea level will rise more than a metre this century – and some have even suggested that the rise could be two metres.

This is mainly because there has been uncertainty about how much of the huge icecap in Greenland, and most of all in Antarctica, would contribute to sea level rise by 2100 – if at all.

Research published since the IPCC estimates were made show that both icecaps will be large net contributors to sea level rise, and possibly much quicker than previously thought.

This lends credibility to the report last week that European coastal cities are not sufficiently prepared for the threats that climate change poses. The report − titled Underfunded, Unprepared, Underwater? Cities at Risk – is by the E3G non-governmental organisation, and it says governments across the European Union are leaving their major cities exposed to danger from climate change, including floods, heat waves and sea level rise.

Since it takes an average of 30 years from planning to complete construction of a major flood barrier to protect a city, the report warns that the problem needs to be given urgent consideration and funding. – Climate News Network

Share This:

Deep concerns as climate impacts on Gulf Stream flow

Deep concerns as climate impacts on Gulf Stream flow

Ocean scientists find evidence of an increasing slowdown in the Atlantic’s “invisible river” that could seriously affect weather and sea levels in the US and Europe.

LONDON, 25 March, 2015 − Climate scientists have once again confirmed an alarming slowdown in the circulation of the Atlantic Ocean − the process that drives the current that warms Europe, and powers the planetary climate.

And this time, they are prepared to say that the changes are recent − and may be linked to global warming.

The Atlantic Conveyor is a great invisible river that flows in two directions at the same time. The equatorial surface waters − warm, and therefore less dense − flow towards the north in the form of the Gulf Stream. Around Greenland, the denser and colder Arctic waters sink to the ocean bottom and begin their progress towards the south.

It is the difference in temperatures that maintains the turnover and keeps the climate engine going.

As a consequence, the two-way traffic of warm and cold water redistributes heat around the planet and keeps Britain and maritime Europe in relatively mild conditions.

But as global average temperatures rise, and the Greenland ice sheet melts, ocean scientists have warned that the speed of the ocean turnover could be put at risk.

Greater weakening

Stefan Rahmstorf, an ocean physicist at the Potsdam Institute for Climate Impact Research in Germany, is lead author of a report in Nature Climate Change that says they now have evidence of a slowdown during the 20th century, and greater weakening since the first alarms 40 years ago about the possible effects of greenhouse emissions.

“It is conspicuous that one specific area in the North Atlantic has been cooling in the past hundred years, while the rest of the world heats up,” Professor Rahmstorf says. “Now we have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970.”

The paradox of the Atlantic current is that, in a warmer world, it could slow down or halt, which would deliver uncomfortable consequences for maritime Europe.

Fears of such an effect provided the scenario for the 2004 climate disaster movie, The Day After Tomorrow, which predicated a frozen Britain and a glaciated US.

“Now we have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970”

No such extreme outcome was ever likely, but the Gulf Stream certainly makes a big difference to Britain. A former UK chief scientist once calculated that it delivered 27,000 times the warmth that Britain’s power stations could supply and, as a consequence, the UK is on average 5°C warmer than it might be, given its latitude.

Strength of current

At a number of points in the last two decades, researchers have wondered about the strength of the Atlantic current, but since systematic oceanographic record-keeping began only relatively recently, they had no way of distinguishing between a natural oceanic cycle and real change.

So the Potsdam team used all available data, and “proxy temperatures” derived from ice-cores, tree-rings, coral, and ocean and lake sediments, to reconstruct the story of the Atlantic current − and, in particular, the phenomenon called the Atlantic meridional overturning circulation (AMOC) − for the last 1,000 years.

The changes happening now have no precedent since 900 AD, they say. And the increasingly rapid melting of the Greenland icecap – bringing an increased flow of water that is less saline and also less dense, and therefore less likely to sink − could disturb the circulation.

The consequences of all this could, they say, “contribute to further weakening of the AMOC” in the coming decades.

Atlantic Conveyor: a graph of the Atlantic Meridional Overturning Circulation (AMOC). Image: Stefan Rahmstorf/PIK

Atlantic Conveyor: a graph of the Atlantic Meridional Overturning Circulation (AMOC).
Image: Stefan Rahmstorf/PIK

This is not the first such alarm. The same weakening was identified last year, but at the time researchers could not be sure they were not looking at a natural fluctuation.

Now they are sure, and they suspect that the cooling of the north Atlantic that they now observe is even stronger than most computer simulations have so far predicted.

“Common climate models are underestimating the change we’re facing, either because the Atlantic overturning is too stable in the models or because they don’t properly account for the Greenland ice sheet melt, or both,” says one of the co-authors, Michael Mann, professor of meteorology at Pennsylvania State University in the US.

Climate predictions

“That is another example where observations suggest that climate model predictions are in some respects still overly-conservative when it comes to the pace at which certain aspects of climate change are proceeding.”

Another of the authors, Jason Box, professor of glaciology at the Geological Survey of Denmark and Greenland, adds that “the human-caused mass loss of the Greenland ice sheet appears to be slowing down the Atlantic overturning − and this effect might increase if temperatures are allowed to rise further”.

The stakes are high. If the Atlantic conveyor system continues to weaken, ocean ecosystems will change, fishing communities will be affected, and some coastal cities – such as New York and Boston in the US − could be hit by additional regional sea level rises.

The 2004 Hollywood version – promoted with a huge poster of New York’s Statue of Liberty all but covered by ice – is not likely to happen. But if the ocean circulation weakens too much, there could be a relatively rapid and difficult-to-reverse change in the world’s climate system.

The Intergovernmental Panel on Climate Change estimates that there is a one-in-10 chance of this “tipping point” happening within the 21st century.

But the evidence from the Potsdam team is now likely to prompt other climate scientists to go back to their calculations and re-evaluate the risk. – Climate News Network

Share This:

More Antarctic warmth creates heavier snowfall

More Antarctic warmth creates heavier snowfall

Rising temperatures may result in more snow falling in Antarctica, with the ice that builds up flowing to the ocean and raising sea levels.

LONDON, 16 March, 2015 – It may sound unlikely, but the evidence is mounting that the more the Antarctic warms under the impact of climate change, the more snow will fall on it.

Not only that, says a team of European and US scientists, but as the snow turns to ice it is going to flow downhill, borne by its own weight, and contribute to rising sea levels.

The impact of this paradoxical process is likely to be significant. The team, led by scientists from Germany‘s Potsdam Institute for Climate Impact Research (PIK), says each degree Celsius of warming in the region could increase Antarctic snowfall by about 5%.

Ice-core data

The research, published in Nature Climate Change, builds on high-quality ice-core data and fundamental laws of physics captured in global and regional climate model simulations.

The suggestion that Antarctic snowfall is increasing is not itself new, though not all scientists accept the data without qualification.

What the Potsdam scientists have done is important, not simply because they provide new evidence to support the contention, but because they explore its potential consequences.

Katja Frieler, climate impacts and vulnerabilities researcher at PIK, and lead author of the report, says: “Warmer air transports more moisture, and hence produces more precipitation. In cold Antarctica, this takes the form of snowfall. We have now pulled a number of various lines of evidence together and find a very consistent result: temperature increase means more snowfall on Antarctica.”

To reach a robust estimate, the PIK scientists collaborated with colleagues in the Netherlands and the US.

“Ice-cores drilled in different parts of Antarctica provide data that can help us understand the future,” says co-author Peter U. Clark, professor of geology and geophysics at Oregon State University.

“The Antarctic ice sheet could become a major contributor to future sea-level rise, potentially affecting millions of people in coastal areas” 

“Information about the snowfall spanning the large temperature change during the last deglaciation [the uncovering of land by the melting of glaciers], 21,000 to 10,000 years ago, tells us what we can expect during the next century.”

The researchers combined the ice-core data with simulations of the Earth’s climate history and comprehensive future projections by different climate models, and were able to pin down temperature and accumulation changes in warming Antarctica.

The increasing snowfall on the continent will add to the mass of the ice sheet and increase its height.

But the researchers say it won’t stay there. On the basis of another previous PIK study, they say the extra snow will also increase the amount of ice flowing to the ocean.

Dr Frieler says: “Under global warming, the Antarctic ice sheet, with its huge volume, could become a major contributor to future sea-level rise, potentially affecting millions of people living in coastal areas.”

Additional snowfall

As snow piles up on the ice, its weight presses down – the higher the ice, the greater the pressure. Additional snowfall elevates the grounded ice-sheet on the Antarctic landmass, but has less of an effect on the floating ice shelves at the coast, allowing the inland ice to flow more rapidly into the ocean and raise sea levels, the researchers say.

The 5% increase in Antarctic snowfall that they expect for every 1°C rise in temperature would mean an estimated drop in sea-level of about three centimetres after a century.

But they say other processes will cause an eventual rise in sea-level. For example, relatively slight warming of the ocean could cause coastal ice to break off more easily, allowing more of the continental ice mass to discharge into the ocean.

Another co-author is Anders Levermann, PIK professor of dynamics of the climate system, and also a lead author of the sea-level rise chapter in the latest report by Intergovernmental Panel on Climate Change.

He says: “If we look at the big picture, these new findings don’t change the fact that Antarctica will lose more ice than it will gain, and that it will contribute to future sea-level change.” – Climate News Network

Share This:

Population increases flood and drought threat to cities

Population increases flood and drought threat to cities

As cities worldwide expand to cope with rising populations, scientists predict a huge increase in urban land vulnerable either to flooding or drought by 2030.

LONDON, 11 March, 2015 − Many of the great coastal cities of America, Asia and Africa will be at increased risk of damaging floods − even without the increasing effects of climate change.

And there will be problems with the other extreme, as scientists also predict that the urban area exposed to drought would double by 2013.

Burak Güneralp, a geographer at Texas A&M University, and colleagues report in the journal Global Environmental Change that by 2030 almost 5 billion people will live in cities, and coastal urban areas will spread out over danger zones of low elevation.

In 2000, about 30% of global urban land – 200,000 square kilometres – was in high-frequency flood zones. By 2030, this will have risen to 40%, or 700,000 square kilometres. And there could also be a growth in the urban extent of drylands 500,000 square kilometres.

Exposed area

So the city regions vulnerable to flood would increase 2.7 times, while the area exposed to drought would double.

The report’s authors says that disasters due to water-related hazards – floods, droughts and windstorms − made up nearly 90% of the 1,000 most catastrophic events between 1900 and 2006 − and because of increasing urbanisation, economic losses have soared.

In the 20 years from 1992-2012, flood and drought hazards caused $600 billion in damage, and in 2013, floods and drought accounted for more than a quarter of all global insured losses.

The message from the authors to tomorrow’s urban planners is: watch where you build new developments or permit new settlement.

“Potential future changes in the extent and layout of urban areas are typically ignored in resilience planning for these cities”

“Urban areas exposed to flood and drought hazards will increase considerably due to the sheer increase in their extents, primarily by socioeconomic forces,” Dr Güneralp says. “In particular, coastal megacities will house a majority of the urban populations, and they will increasingly be hubs of significant economic activity in the coming decades.

“Yet potential future changes in the extent and layout of the urban areas are typically ignored in resilience planning for these cities.”

The Texas team made their calculations with geographic information systems, existing urban maps and city growth forecasts. They did so without factoring in climate change, but they warn that all hazards will be amplified by rising average global temperatures.

Human numbers exposed to a once-a-century flooding event in 136 port cities across the world are expected to increase threefold by 2070, and their economic infrastructure –roads, houses, power and water services, offices and factories – will increase tenfold.

Water shortages

Meanwhile, the number of city-dwellers who could face perennial water shortages is expected to increase fivefold by 2050 − to around 160 million people.

The Texas scientists considered the great delta cities of China, Vietnam and India, but they also included the American megalopolises of New York, Baltimore, Houston and Miami, which are all vulnerable in their own ways.

Their research reinforces fresh reminders – on the eve of yet another disaster risk reduction conference, in Sendai, Japan − that global disasters of all kinds claimed 700,000 lives, changed the lives of 1.7 billion people, and cost cities and states at least $1.4 trillion in the last 10 years.

And 87% of these disasters were climate-related, according to the UN International Secretariat for Disaster Reduction. − Climate News Network

Share This:

Greenland’s hidden meltwater lakes store up trouble

Greenland’s hidden meltwater lakes store up trouble

Scientists find evidence of vast “storage tanks” of water deep below the melting Greenland ice sheet that could have a major effect on sea level rise.

LONDON, 5 February, 2015 − One small mystery that surrounds Greenland’s melting ice is a little closer to being solved as scientists in the US confirm that surface meltwater can drain all the way down to fill concealed lakes under the ice.

This means that atmospheric warming can reach thousands of metres below the ice sheet − warming the glacial base and potentially increasing its rate of flow.

One group, led by geologist Michael Willis, of Cornell University, and another team led by glaciologist Ian Howat, of Ohio State University, report in two different journals on separate but related studies of Greenland’s plumbing system: what happens to meltwater.

The ice sheet of Greenland adds up to about four-fifths of the mass of the vast frozen island, and there is evidence that, as a consequence of global warming, the rate of melting has begun to accelerate.

Measurable difference

This has already begun to make a measureable difference to global sea levels, and were the entire island to shed its burden of ice – a process that would take a considerable time − then sea levels would rise by seven metres or more.

So what exactly happens to the water that forms on the surface and collects in lakes each summer, and how much of it gets into the sea, has become an important but perplexing problem. Surface lakes are now appearing much further inland, and at higher altitudes, than recorded in the past.

Dr Howat and his colleagues report in The Cryosphere that they measured a two kilometre-wide depression 70 metres deep in the icecap of southwest Greenland, which they then identified as “the first direct evidence for concentrated long-term storage and sudden release of meltwater at the bed”.

The slumped crater suggested a holding capacity of more than 30 million cubic metres of water, which had suddenly drained away.

“If we are going to do something to mitigate sea level rise, we need to do it earlier rather than later”

“The fact that our lake appears to have been stable for at least several decades, and then drained in a matter of weeks – or less – after a few very hot summers, may signal a fundamental change happening to the ice sheet,” Dr Howat said.

The Cornell team worked in northeast Greenland, and in 2011 found a collapsed basin 70 metres deep. Dr Willis and colleagues report in Nature journal that between 2011 and 2014 they watched as summer meltwater made its way down fissures in the depression and refilled a lake basin at the base of the icecap. When this in turn emptied, the researchers calculated that the flow from the subglacial lake was at a rate of 215 cubic metres per second.

“We’re seeing surface meltwater make its way to the base of the ice where it can get trapped and stored at the boundary between the bedrock beneath the ice sheet and the ice itself,” they say.

“As the lake beneath the ice fills with surface meltwater, the heat released by this trapped meltwater can soften surrounding ice, which may eventually cause an increase in ice flow.”

Glacial flow

The researchers do not yet know whether the draining water is increasing glacial flow, and nor can they be sure how many such depressions in the Greenland ice mask buried meltwater storage tanks.

But melting of glacial ice is likely to accelerate anyway, according to new research in the journal Climate Dynamics.

Earth scientist Patrick Applegate, of Penn State University, reports that computer models confirm that the more temperatures increase, the faster the ice will melt.

Were all Greenland’s ice to melt, sea levels would rise catastrophically. At least one billion people live on coasts and estuaries vulnerable to a mere one metre rise.

The Arctic is already the fastest warming place in the northern hemisphere, and the Penn State scientists wanted to see how present warming could play back into future warming. Engineers call this positive feedback.

“If we are going to do something to mitigate sea level rise, we need to do it earlier rather than later,” Dr Applegate said. “The longer we wait, the more rapidly the changes will take place and the more difficult it will be to change.” − Climate News Network

Share This:

Arctic glacier’s galloping melt baffles scientists

Arctic glacier’s galloping melt baffles scientists

New satellite data analysis has produced evidence that rapid melting in the last three years has caused dramatic shrinkage of an Arctic ice cap.

LONDON, 31 January, 2015 – An ice cap in the high Arctic has lost what British scientists say is a significant amount of ice in an unusually short time.

It has thinned by more than 50 metres since 2012 – about one sixth of its original thickness – and the ice flow is now 25 times faster, accelerating to speeds of several kilometres per year.

Over the last two decades, thinning of the Austfonna ice cap in the Svalbard archipelago − , roughly half way between Norway and the North Pole − has spread more than 50km inland, to within 10km of the summit. .

A team led by the scientists from the UK Centre for Polar Observation and Modelling (CPOM) at the University of Leeds combined observations from eight satellite missions, including Sentinel-1A and CryoSat, with results from regional climate models, to understand what was happening.

Sea level rise

The study’s lead author, geophysicist Dr Mal McMillan, a member of the CPOM team, said: “These results provide a clear example of just how quickly ice caps can evolve, and highlight the challenges associated with making projections of their future contribution to sea level rise.”

The study, published in Geophysical Research Letters, is the first to make use of measurements from the European Space Agency’s latest Earth observation satellite, Sentinel-1A.

Dr McMillan said: “New satellites, such as the Sentinel-1A and CryoSat missions, are essential for enabling us to systematically monitor ice caps and ice sheets, and to better understand these remote polar environments.”

“Whether or not the warmer ocean water
and ice cap behaviour are directly linked
remains an unanswered question”

Melting ice caps and glaciers account for about a third of recent global sea level rise. Although scientists predict that they will continue to lose ice in the future, determining the exact amount is difficult, because of a lack of observations and the complex nature of how they interact with the climate around them.

The 20 years of satellite data that the scientists have amassed show some fairly small changes at the start of the study period, but these have since increased.

“Glacier surges, similar to what we have observed, are a well-known phenomenon”, said Professor Andrew Shepherd, the director of CPOM. “What we see here is unusual because it has developed over such a long period of time, and appears to have started when ice began to thin and accelerate at the coast.”

There is evidence that the surrounding ocean temperature has increased in recent years, which may have been the original trigger for the ice cap thinning.

Flow models

Prof Shepherd said: “Whether or not the warmer ocean water and ice cap behaviour are directly linked remains an unanswered question. Feeding the results into existing ice flow models may help us to shed light on the cause, and also improve predictions of global ice loss and sea level rise in the future.”

The team says long-term observations by satellites are the key to monitoring such climate-related phenomena.

Dr McMillan told Climate News Network he did not think what was happening in Austfonna suggested any sort of tipping point in the Arctic, which scientists say is warming more than twice as fast as anywhere else on Earth.

He said: “What I take from this work is that we don’t understand well enough what’s caused this sort of behaviour − natural variability, ocean temperatures or atmospheric temperatures. It reinforces the complexities and the challenges of the future.” – Climate News Network

Share This:

Scientists say rise in sea levels is faster than feared

Scientists say rise in sea levels is faster than feared

Harvard researchers find that there has been an almost threefold annual increase in global sea levels over the last quarter of a century.

LONDON, 22 January, 2015 − Sea level rise for most of the 20th century may have been over-estimated by as much as 30%. But the less welcome news is that, if that’s the case, then sea levels since 1990 have started to accelerate more sharply than anyone had ever expected.

Scientists at Harvard University, in the US, report in the journal Nature that they came to the conclusions after deciding that old data needed fresh analysis − using sophisticated mathematical filtering techniques for handling the uncertainties and gaps in such data.

Estimating and accounting for global mean sea level (GMSL) rise is critical to characterising current and future human-induced changes. The catch is that sea level measurement hasn’t been going on for very long, so not all measurement techniques have been the same. In addition, reliable, systematic and sustained sets of data are relatively sparse.

Rise and fall

The term “sea level” sounds pretty basic, but the oceans are hardly ever level. Tides swell and ebb, regions of sea rise and fall according to temperature and salinity, and the shorelines at which researchers take measurements can also go up because of tectonic movement or sink because of the abstraction of groundwater.

Measurements along some of the world’s great estuary systems can be skewed because of human interference over the decades with the flow downstream, and great tracts of ocean cannot be measured directly at all.

The challenge, then, is to arrive at an average sea level rise for the whole planet.

“We know that sea level is changing for a variety of reasons,” said Dr Carling Hay, post-doctoral fellow in Harvard’s Department of Earth and Planetary Sciences (EPS).

“There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present day melting of land-ice − all of which result in unique patterns of sea level change. These processes combine to produce the observed global mean sea level rise.”

So the Harvard scientists, working with colleagues from Rutgers University in New Jersey, made estimates for the meltwater from glaciers and dwindling ice caps, from ocean thermal expansion and factors. They then “smoothed” the data, using a mathematical modelling algorithm.

Earlier estimates put mean sea level rise in the 20th century at between 1.5 and 1.8 millimetres a year. Dr Hay and her colleagues now think that, between 1901 and 1990, the true figure was probably closer to 1.2mm a year.

But since 1990, global sea level has risen by 3mm a year on average. So, in fact, the acceleration since then has been faster than anybody expected – and this in turn could affect future projections.

Question of accuracy

“Another concern with this is that many efforts to project sea level change into the future use estimates of sea level rise over the time period from 1900 to 1990,” said co-author Eric Morrow, a recent Ph.D graduate of Harvard’s EPS

“If we’ve been over-estimating the sea level change during that period, it means that these models are not calibrated appropriately, and that calls into question the accuracy of projections out to the end of the century.”

Dr Hay added: “We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5 to 1.8mm a year that other people had predicted. But the math doesn’t work out that way.

“Unfortunately, our new lower rate of sea level rise prior to 1990 means that sea level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought.” – Climate News Network

Share This:

Science gains from clearer sight of Greenland’s ice melt

Science gains from clearer sight of Greenland's ice melt

Research into how Greenland’s ice melts should lead to more accurate predictions of sea level rise and global warming.

LONDON, 18 January, 2015 − Scientists in the US have used on-the-ice measurements and military-grade satellite imagery to take a much closer look at just how Greenland’s icesheet melts.

They already knew that huge icebergs fall from the glaciers into the ocean, and that surface lakes drain suddenly in the summer warmth. But now they know considerably more about what happens to the network of streams, rivers and ponds that collect in the summer sunshine, and then flow across the top of the icesheet into moulins, or sinkholes.

They report in the Proceedings of the National Academy of Sciences that they used the data collected to chart 523 streams in a catchment area of about 6,800 square kilometres during the freak thaw of 2012, when almost the whole of the Greenland icecap was covered in slush. They measured the run-off at between 1,550 and 1,700 cubic metres per second − twice the average flow of the Colorado River.

Thereafter, all this water drained into moulins, and began to filter towards the base of the icesheet. What happened to it then is not yet certain, but the guess is that a percentage was soaked up within the iceshelf, while a proportion reached the sea.

Only the start

The study placed 11 researchers on the ice for six days in July 2012, during a massive and unusual melt. Only on one other occasion in the last 700 years, in 1889, did Greenland’s ice melt on such a scale.

The scientists were moved around by helicopter and equipped with a specially-designed automaton boat, buoys fitted with GPS technology, and sophisticated satellite imagery.

“It was a real preview of just how quickly that ice sheet can melt and the meltwater can escape”, said lead author Laurence Smith, Professor of Earth, Planetary, and Space Sciences at University of California Los Angeles. “The question was whether the ice sheet acts like a sponge or like Swiss cheese.”

The provisional answer is: both. Some meltwater stays, and some certainly escapes altogether. But it will take more than just one visit to arrive at more precise calculations.

“Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial”

The scientists also took measurements of Greenland’s Isortoq river − just one of about 100 large terrestrial rivers delivering Greenland meltwater to the oceans.

They found that the Isortoq carries water from the ice sheet to the ocean at between 650 and 1,300 cubic metres per second, which is less than models have projected.

Such direct measurements are important because they make predictions of melt rate and sea level rise more accurate − and more credible.

“If we can get better estimates, then we can have better projections for the extent and impact of global warming”, said another of the report’s authors, Marco Tedesco, founder and director of the City College of New York’s Cryospheric Processes Laboratory. “Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial.” – Climate News Network

Share This:

US coastal cities warned of daily high tide floods

US coastal cities warned of daily high tide floods

Scientists report that many cities near the coasts of the US should prepare for daily flooding at high tide by mid-century because of rising sea levels.

LONDON, 5 January, 2015 − Oceanographers have just identified the US coastal regions likely to experience 30 days or more of “nuisance” flooding every year. And the answer is that most of the American coast will experience high waters that are 30-60 cms above local high tides, at least 30 times a year.

Nuisance flooding means just that − somewhere between an inconvenience and modest damage. But climate change, and its attendant sea-level rise, will make them much more frequent, and possibly more damaging.

William Sweet and Joseph Park, scientists at the National Oceanic and Atmospheric Administration (NOAA), report in the journal Earth’s Future that sea level rise has accelerated from 1.7mm a year in the last century to 3.2mm a year in the last two decades, and flooding events that were once extreme could become the mean.

The oceanographers wanted to establish what they call “regional tipping points” – places where extra high waters would wash across streets and promenades normally above water and start to do so frequently.

Detailed picture

New York was inundated when Superstorm Sandy hit the city in 2012, and studies have repeatedly warned that coastal inundations will cost communities colossal sums each year by 2050, and even more by 2100. Nor is the US alone in this respect. There have been ominous calculations for the UK as well.

The NOAA scientists add detail to the big picture. They started with the projections for global sea level rise delivered by the Intergovernmental Panel on Climate Change and then included the more local factors such as land subsidence or settlement, and cyclic weather patterns that exacerbate the tidal highs. Such floods have already increased, and are now five to 10 times more likely than 50 years ago.

They looked at all those tidal stations with a continuous 50-year record of measurement. This does not include the city of Miami, where the tide stations were destroyed in 1992 by Hurricane Andrew.

Coastal changes

And they warn that Boston, New York City, Philadelphia, Baltimore and many other places along the Atlantic Coast, Galveston and Port Isabel in the Gulf of Mexico, and San Francisco Bay and San Diego along the Pacific Coast will all see a lot more seawater in city streets.

“Coastal communities are beginning to experience sunny-day nuisance flooding, much more so than in decades past,” said Dr Sweet. “This is due to sea level rise.

“Unfortunately, once impacts are noticed, they will become commonplace rather quickly. We find that in 30 to 40 years, even modest projections of global sea level rise – 1.5 feet by the year 2100 – will increase instances of daily high tide flooding to a point requiring an active and potentially costly response.

“And by the end of the century, our projections show that there will be near-daily nuisance flooding in most of the locations that we reviewed.” – Climate News Network

Share This: