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Greenland’s icecap loses stability

April 13, 2014 in Arctic, Glaciers, Greenland, Ice Loss, Sea level rise, Warming

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The calving front of the Jakobshaven Glacier in western Greenland in April 2012 Image: NASA ICE via Wikimedia Commons

The calving front of the Jakobshaven Glacier in western Greenland in April 2012
Image: NASA ICE via Wikimedia Commons

By Tim Radford

Greenland is losing ice from part of its territory at an accelerating rate, suggesting that the edges of the entire ice cap may be unstable.

LONDON, 13 April – Greenland – the largest terrestrial mass of ice in the northern hemisphere – may be melting a little faster than anyone had guessed.

A region of the Greenland ice sheet that had been thought to be stable is undergoing what glaciologists call “dynamic thinning”. That is because the meltwater from the ice sheet is getting into the sea, according to a study in Nature Climate Change.

In short, Greenland’s contribution to sea level rise has been under-estimated, and oceanographers may need to think again about their projections.

Shfaqat Khan from the Technical University of Denmark and colleagues used more than 30 years of surface elevation measurements of the entire ice sheet to discover that overall loss is accelerating. Previous studies had identified melting of glaciers in the island’s south-east and north-west, but the assumption had been that the ice sheet to the north-east was stable.

Four times as fast

It was stable, at least until about 2003. Then higher air temperatures set up the process of so-called dynamic thinning. Ice sheets melt every Arctic summer, under the impact of extended sunshine, but the slush on the glaciers tends to freeze again with the return of the cold and the dark, and since under historic conditions glaciers move at the proverbial glacial pace, the loss of ice is normally very slow.

But global warming, triggered by rising levels of greenhouse gases in the atmosphere, has changed all that. Greenland’s southerly glaciers have been in retreat and one of them, Jakobshavn Isbrae, is now flowing four times faster than it did in 1997.
Now the Danish-led team has examined changes linked to the 600 kilometre-long Zachariae ice stream in the north-east.

This has retreated by about 20 kms in the last decade, whereas Jakobshavn has retreated about 35 kms in 150 years. The Zachariae stream drains around one-sixth of the Greenland ice sheet, and because warmer summers have meant significantly less sea ice in recent years, icebergs have more easily broken off and floated away, which means that the ice stream can move faster. The researchers used satellite studies to measure ice loss.

“North-east Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet,” said one of the team, Michael Bevis of Ohio State University in the US.

Deep impacts

“This study shows that ice loss in the north-east is now accelerating. So now it seems that all of the margins of the Greenland ice sheet are unstable.”

The scientists used a GPS network to calculate the loss of ice. Glacial ice presses down on the bedrock below it: when the ice melts, the bedrock rises in response to the drop in pressure, and sophisticated satellite measurements can deliver enough information to help scientists put a figure on the loss of ice.

They calculate that between April 2003 and April 2012, the region was losing ice at the rate of 10 billion tons a year.

“This implies that changes at the margin can affect the mass balance deep in the centre of the ice sheet,” said Dr Khan. Sea levels are creeping up at the rate of 3.2 mm a year. Until now, Greenland had been thought to contribute about half a mm. The real figure may be significantly higher. – Climate News Network

Rising sea levels threaten Los Angeles

February 22, 2014 in Drought, Extreme weather, Sea level rise, Temperature Increase, USA

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Residents of the Cabrillo Marine Aquarium, one of the Los Angeles buildings at risk from sea level rise Image: By Jllm06 via Wikimedia Commons

Residents of the Cabrillo Marine Aquarium, one of the Los Angeles buildings at risk from sea level rise
Image: By Jllm06 via Wikimedia Commons

By Tim Radford

As much of California and the western US endures a severe drought, the city of Los Angeles is at increasing risk from rising sea levels, researchers say.

LONDON, 22 February – Los Angeles, City of the Angels in southern California, sits on a flat shelf of the Pacific coast of America, with a view of the sea. And if climate scientists are right, it could soon have an even closer view of the sea.

The city of more than 12 million people occupies 12,000 square kilometres of land, much of it no more than three metres above sea level. By 2050, rising sea levels could pose a threat to the infrastructure, museums and historic buildings of this great capital of entertainment, education, business, tourism and international trade, according to a new study by the University of Southern California.

“Some low-lying areas within the city’s jurisdiction, such as Venice Beach and some areas of Wilmington and San Pedro, are already vulnerable to flooding”, says Phyllis Grifman, lead author of the report, commissioned by the city and the USC Sea Grant Program.

“Identifying where flooding is already observed during periods of storms and high tides, and analyzing other areas where flooding is projected, are key elements to effective planning for the future.”

The city has already started to prepare for climate change: in June last year it published a report from the University of California Los Angeles on the pattern of snow fall and spring melt over recent decades and the ominous message for winter sports and summer water levels.

Double bind

Climate scientists expect the south-west of the US to become more arid as the century advances, and California has been in the grip of recent, unprecedented drought. But as glaciers melt and retreat, and the oceans warm and expand, the City of the Angels could find itself between the devil and the deep blue sea.

Sea levels are expected to rise somewhere between 0.6 metres and 1.7 metres by the close of the century. Peak tides and storm surges already present problems: as sea levels rise, these will become more damaging.

The drains that carry off its storm water and sewage, and deliver clean water from the mountains, could all be at risk from marine incursion. Floods and erosion could wear away the coast roads, and many museums and historic buildings, including the Cabrillo Marine Aquarium, could face damage. In 2012, Los Angeles attracted 41 million tourists who accounted for a total spending of more than $16 billion.

Some coastal communities, the report says “are home to highly vulnerable populations” already struggling with low incomes, linguistic isolation, older housing stock and lower education levels.

And a serious storm – the once-in-a-decade storm – could exact financial losses of $410 million if sea levels rise by half a metre. If they rise by about one and a half metres, the economic costs could tip more than $700 million. – Climate News Network

Coastal flooding ‘may cost $100,000 bn a year by 2100′

February 11, 2014 in Climate finance, Coastal Threats, Extreme weather, Flooding, Sea level rise, Warming

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The only way is up: A rapid start on cutting emissions is essential Image: Jan Smith via Wikimedia Commons

The only way is up: A rapid start on cutting emissions is essential
Image: Jan Smith via Wikimedia Commons

By Tim Radford

On the world’s present course, the cost by 2100 of tackling coastal flooding could be beyond the reach of the poorest countries – and ruinously expensive for richer ones.

LONDON, 11 February – If global warming continues on its present ominous path, and if no significant adaptation measures are launched, then coastal flooding could be costing the planet’s economies $100,000 billion a year by 2100.

And perhaps 5% of the people on the planet – up to 600 million people – could be hit by coastal flooding by the end of the century, according to new research in the Proceedings of the National Academy of Sciences.

Jochen Hinkel from the Global Climate Forum in Berlin and colleagues have compiled, for the first time, global simulation results on future flood damage to buildings and infrastructure on the world’s coastal flood plains.

They expect drastic increases in economic damage because, as sea levels rise with the decades, so will population and investment: there will be more people with more to lose.

Right now, coastal floods and storm surge damage cost the world between $10 billion a year and $40 billion. But as the megacities grow – think of Lagos, or Shanghai, or Manila – more people will be at risk, and, among them, greater than ever numbers of the poorest.

“If we ignore this problem, the consequences will be dramatic,” says Hinkel. “Countries need to take action and invest in coastal protection measures, such as building or raising dykes, amongst other options.”

Provoking a response

And his co-author Robert Nicholls from the University of Southampton warns: “If we ignore sea level rise, flood damages will progressively rise and presently good defences will be degraded and ultimately overwhelmed, hence we must start to adapt now.”

All such projections involve assumptions about the future that cannot be tested, so the authors spread their bets: they considered a range of scenarios involving crude population growth, levels of economic growth with time, and a series of predictions of sea level rise, as icecaps and glaciers melt, and as the oceans warm and expand according to predictable physical laws.

What they could not predict – because such things require political decisions of the kind they hope to provoke with their forecasts – would be the civic and political responses in the next eight decades as storms become more violent and floods more frequent.

Nor did they try to incorporate the natural consequences of human settlement: how much subsidence, for instance, would occur as humans pumped groundwater from aquifers or quarried strata for building material, all things that would lower the levels of the land already at risk from invasion by the sea.

But their predictions, while alarming, are only reinforcements of earlier investigation. In August a World Bank team calculated that floods would be routinely costing coastal cities $1 trillion a year by 2050.

In July last year, a team from Stanford University in California looked at the challenge of building sea defences and proposed that by far the most efficient solutions would all be natural: dune systems, mangrove forests, reefs, water meadows, kelp forests and natural estuary ecosystems provided the best protection for many people in many circumstances.

And in December scientists from the University of Massachusetts considered the devastation wreaked on New York and other American cities by Superstorm Sandy in October 2012 and warned that such things could happen again and that, once again, natural systems might provide the most efficient  buffers against the buffetings of the weather.

Huge losses

The PNAS authors consider for the purpose of their argument only the increasing costs of either maintaining sea barriers such as dykes, or raising them.

By 2100, global average sea level rise could be as low as 25 cms, or as high as 123 cms; between 0.2% and 4.6% of the world’s population could be affected by flooding each year; and losses could be as low as 0.3% or as high as 9.3% of global gross domestic product.

It doesn’t matter very much whether by the end of the century the losses hit the low end of these projections, or the high. They will always be huge. “Damages of this magnitude are very unlikely to be tolerated by society and adaptation will be widespread”, the authors warn.

And there will be tracts of land that no dykes could ever save from the rising waters. The poorest countries are in any case unlikely to be able to meet the costs of sustained protection from the sea.

“If we do not reduce greenhouse gases swiftly and substantially, some regions will have to seriously consider relocating significant numbers of people in the longer run”, says Hinkel. He and his co-authors want to see some significant long-term thinking.

His colleague Professor Nicholls adds: “This long-term perspective is however a challenge to bring about, as coastal development tends to be dominated by short-term interests of, for example, real estate and tourism companies, which prefer to build directly on the waterfront with little thought about the future.” – Climate News Network

Greenland’s fastest glacier picks up pace

February 6, 2014 in Arctic, European Space Agency, Glaciers, Greenland, Ice Loss, Lakes, Sea level rise

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An iceberg calved from the rapidly accelerating Jakobshavn Isbræ floats in Greenland's Disko Bay Image: Courtesy of Ian Joughin, PSC/APL/UW

An iceberg calved from the rapidly accelerating Jakobshavn Isbræ floats in Greenland’s Disko Bay
Image: Courtesy of Ian Joughin, PSC/APL/UW

By Tim Radford

Research from the Arctic shows Greenland’s fastest-flowing glacier has doubled its summer flow pace in a decade, and ice cover on Alaskan lakes is declining.

LONDON, 6 February – A fast-moving Arctic glacier which has earned a place in history is now accelerating even more quickly. The Jakobshavn Isbrae (the Danish word for glacier) is a massive river of ice from the Greenland ice sheet to an Atlantic ocean fjord and is thought – there is no way of proving this – to be the source of the giant iceberg that sank the Titanic in 1912.

According to research published in the European Geosciences Union journal The Cryosphere, summer flow speeds have doubled yet again since a Nasa measurement in 2003. And that in turn represented a doubling of flow speeds since 1997.

The Jakobshavn glacier is Greenland’s fastest-flowing glacier. It now moves at 17 kilometres a year. That works out at 46 metres a day. With accelerations like this, phrases like “glacial pace” may no longer serve as clichés of lethargic movement. These speeds are recorded in the summer, when all glaciers are more likely to be a bit friskier. But even when averaged over the whole year, the glacier’s flow has accelerated threefold since the 1990s.

Icebergs “calve” from glaciers – they break off and drift out to sea. The Arctic ice sheet is thinning, and most of the planet’s glaciers are retreating as climates warm, so the Jakobshavn glacier is carrying less ice, at a faster rate, over shorter distances than ever before, and by the end of the century could have shifted 50 kilometres upstream. But right now it is also contributing to sea level rise at a faster rate.

“We know that from 2000 to 2010 this glacier alone increased sea level by about 1mm”, said Ian Joughin, of the Polar Science Centre at the University of Washington, who led the research. “With the additional speed it will likely contribute a bit more than this over the next decade.”

The scientists used satellite data to measure the rate of summer change in Greenland. But other satellite radar imagery has begun to reveal an ominous picture of change elsewhere in the Arctic, on the north slope of Alaska. Even during the winter months, ice on the lakes of Alaska has begun to decline. Warmer climate conditions means thinner cover on shallow lakes and a smaller fraction that freeze entirely during the winter months.

“We were stunned to observe such a dramatic ice decline during a period of only 20 years”

Cristina Surdu of the University of Waterloo in Canada and colleagues report in The Cryosphere that there has been a 22% fall in grounded ice – frozen from surface to lakebed – between 1991 and 2011.

They expected to find a decline in ice thickness when they embarked on a study of radar observations of 402 lakes near Barrow in Alaska from the European earth resources satellites ERS-1 and ERS-2. That was because they already had temperature and precipitation records from Barrow dating back five decades.

Freeze dates in the region are now occurring on average six days later than in the past, and the ice is breaking up on average around 18 days earlier.

“At the end of the analysis, when looking at trend analysis results, we were stunned to observe such a dramatic ice decline during a period of only 20 years”, Surdu said. – Climate News Network

Natural defences can best protect coasts

December 5, 2013 in Adaptation, Coastal Threats, Extreme weather, Sea level rise, Wetlands

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Jon Woodruff and UMass Amherst colleague Christine Brandon survey sediments after Superstorm Sandy Image: Courtesy of UMass Amherst

Jon Woodruff and Christine Brandon survey sediments after Superstorm Sandy
Image: Courtesy of UMass Amherst

 

By Tim Radford

Many shorelines around the world are at risk – not just from extreme weather, but from far more gradual threats. And often the best protection comes from nature.

LONDON, 5 December – It isn’t just the catastrophic storms and tropical cyclones that threaten disaster for the world’s coastal cities. Simple, insidious things like sea level rise, coastal subsidence and the loss of wetlands could bring the sea water coursing through city streets in the decades to come.

Jonathan Woodruff of the University of Massachusetts Amherst in the US and colleagues report in Nature that shorelines are increasingly at risk, and humans must adapt and learn to live with increasing hazard.

Many of the world’s great cities are on low-lying coastal plains, or on river estuaries, and are therefore anyway at risk as sea levels rise because of global warming.

But human action too – by damming rivers, by extracting ground water and by building massive structures on sedimentary soils – has accelerated coastal subsidence. Add to this the possibility of more intense tropical cyclones as sea surface temperatures rise, and coastal cities face a stormy future.

On 29 October 2012 Superstorm Sandy brought a surge of sea water into the streets, subway tunnels and basements of New York City and caused $65 billion worth of damage along the entire eastern seaboard of the US. It was an unprecedented event. But it may happen again.

Facing the future

“A rise in sea level of one metre for the New York City region would result in the present-day 100-year flood events occurring every three to 20 years”, warn Woodruff and his fellow scientists in their Nature study.

“Most engineered coastlines are not designed for this increase in extreme flood frequency, and the dominance of sea level rise and landscape dynamics on impacts by landfalling tropical cyclones must be acknowledged for effective planning and management of our future coastlines.”

The scientists reviewed nearly 100 research studies of coastal change. They also noted that, according to an international register of disasters, more than 60% of economic losses – around $400 bn – occurred in the North Atlantic, one of the areas least at risk from tropical hurricanes. The lesson is that governments and civic authorities will need to think more carefully about future threats.

“Sea-level rise, severe storms, changing climate, erosion and policy issues are just some of the factors to assess in order to understand risk”, says another of the authors, Jennifer Irish of Virginia Tech College of Engineering.

“We reviewed just three of the physical factors – tropical cyclone climatology, sea-level rise and shoreline change. If we look at them separately, we don’t see how they are interconnected.

Relying on natural buffers

“But if we pull back to look at the whole picture, we stand a better chance of protecting our homes, roadways, energy and water networks, and the most critical and expensive infrastructure along the coastlines.”

Other authors in the Nature special feature on coastal threats argue that rather than restore costly sea walls and other engineered coastal defences, it might be more efficient to restore tidal marshes, coastal wetlands, barrier islands and other natural ecosystems that have traditionally served as buffer zones for coastal-dwelling communities.

Two other scientists believe that natural buffers could keep pace with sea level rise and offer continuing protection.

“Tidal marsh plants are amazing ecosystem engineers that can raise themselves upward if they remain heathy, and especially if there is sediment in the water,” says Patrick Megonigal of the Smithsonian Environmental Research Center, one of the authors.

“We know there are limits to this, and worry those limits are changing as people change the environment.” – Climate News Network

Warsaw – Day 3: World faces more ‘perfect storms’

November 13, 2013 in Africa, Australia, Drought, Europe, Extreme weather, Flooding, Heatwave, Sea level rise, South America

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Angola's national tree, the imbondeiro or baobab, helped it through the 2013 drought Image: Alfred Weidinger via Wikimedia Commons

Angola’s national tree, the imbondeiro or baobab, helped it through the 2013 drought
Image: Alfred Weidinger via Wikimedia Commons

By Paul Brown in Warsaw

One of the Climate News Network editors, Paul Brown, is in the Polish capital, host of the UN climate talks – the 19th Conference of the Parties (COP 19) of the United Nations Framework Convention on Climate Change. His latest report describes records continuing to tumble as sea levels rise and warming continues in 2013.

 

The world continues to heat up in 2013, with regional temperature records being broken and sea level rise accelerating, the World Meteorological Organisation (WMO) says in its latest report, Provisional Statement on Status of Climate in 2013.

Sea level rise was particularly significant in the Pacific around the Philippines and had contributed greatly to the devastation caused by the super-typhoon Haiyan, Jerry Lengoasa, deputy general secretary general of the WMO, said here.

The population should have been warned about the tsunami effect of a seven-metre storm surge caused by the typhoon, he said, so that they could have been better prepared to retreat to higher ground.

With the typhoon season not over yet there had already been 30 named storms in the Pacific this year; this was above the average of the last three decades.

Mr Lengoasa said: “What the science tells us is not that there will be more storms, but that the storms we do have will be more violent. ‘Perfect storms’, if we can call them that, like hurricane Sandy last year and typhoon Haiyan this year will become the normal.”

Sea level had risen a third of a metre in the central Philippine area since 1901, making the area much more vulnerable to storm surges. The average sea level rise round the globe was much lower but was speeding up, and was now 3.2 millimetres a year. This is double the annual average of the last century – 1.6 mm.

Australian heatwave

Mr Lengoasa made special mention of the unprecedented heatwave in Australia, which had the hottest month ever observed in January 2013, and the hottest summer on record. On 7 January a new national averaged daily maximum for Australia was set at 40.3°C, and Moomba in South Australia reached 49.6°C.

At the same time as Mr Lengoasa was speaking the Australian Government was being attacked in a nearby meeting for watering down its commitments to tackle climate change.

The German organisation Climate Analytics said that Prime Minister Tony Abbott’s plans to dismantle the current climate legislation in his country could lead to Australia increasing emissions in 2020 rather than meeting its target of reducing them by 5% on their 2000 levels.

Even the 5% target was inadequate and consistent with an increasing global temperature rise of 3.5 to 4°C, well above the 2°C danger level that world leaders have agreed must not be exceeded.  Climate Analytics claimed that under the Abbott plan emissions would increase by 12% by 2020.

Australia ‘the new climate pariah’

Bill Hare, director of Climate Analytics, said: “The existing legislation would have bent the relentless upward curve of Australian emissions downwards, a first step towards a low carbon, climate-safe future. The new policy will see this dismantled and replaced by a climate policy that goes against the science.”

An Australian climate campaigner for Climate Action Network, Julie-Anne Richards, said her country was the new pariah in climate action. “Even the United States and China take more action in fighting climate change than Australia”, she said.

Mr Lengoasa’s presentation was a summary of the weather statistics up to the end of September this year. He said that the year was on course to be among the ten hottest years ever recorded, and warmer than both 2011 and 2012. “It looks as if after a dip during the La Niña episodes, the temperatures are rising again”, he said, cautioning that the statistics were for nine months only.

The year had also been notable for regional floods and droughts. In South America, much below average rainfall was recorded in North East Brazil, where parts of the region suffered their worst drought in 50 years. The Brazilian plateau, the monsoon region of South America received the least rainfall since records began in 1979. The southern African countries of Angola and Namibia “were gripped by one of the worst droughts in the past 30 years.”

At the other extreme in Europe Germany, Poland, the Czech Republic, Austria and Switzerland had intense and extended flooding in late May and early June, and the West African summer monsoon brought welcome rainfall over most of central and western parts of the Sahel. – Climate News Network

Ocean warming narrows climate options

September 28, 2013 in Antarctic, Arctic, Climate, Global Ocean Commission, Greenland, Marine ecology, Ocean acidification, Polar ice, Sea level rise

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Sunrise at Southwold in eastern England: What is happening in the deep oceans? Image: Brenda and Ken Bent via Wikimedia Commons

Sunrise at Southwold in eastern England: What is happening in the deep oceans?
Image: Brenda and Ken Bent via Wikimedia Commons

Professor Chris Rapley is a former director of both the British Antarctic Survey and  the Science Museum in London. What the IPCC’s Fifth Assessment Report, AR5, says about the oceans alarms him.

LONDON, 28 September – The messages are ever clearer: climate change is real, we humans are the driver, and we need to act resolutely and soon to reduce the risk of serious disruption.

The IPCC’s latest report took over 250 experts from 39 countries to sift 9,000 pieces of scientific research and address over 54,000 comments under the close scrutiny of 190 governments. The result: a fresher and sharper image of the physical state of our planet and the changes it is undergoing.

It confirms that each of the most recent three decades has been warmer than its predecessor and that the change – almost 1°C since the beginning of the last century – is significant on a timescale of ten thousand years.

In the context of an unabated planetary energy imbalance, and evidence that the 93% of the energy build-up taken up by the oceans continues to accumulate, the recent slow-down in the rise of surface temperatures, much heralded by the climate dismissers, appears a minor and temporary fluctuation.

In the meantime, the melting and retreat of polar ice shocks experts such as myself – with the loss of ice from Greenland and Antarctica both having increased by a factor of 5-6 over the decades 1990-1999 and 2000-2009.

“…we are fast losing the possibility of restricting warming to 2°C.”

The consequence? In combination with ocean thermal expansion, an accelerating rise in global mean sea level, currently running at 35 cm per century. This is already approaching one third of the rate sustained for 10,000 years during the transition from the last Ice Age to the current warm period, when sea level rose by 120 metres.

The predictions? That we are fast losing the possibility of restricting warming to 2°C. We have at most half a trillion tons of carbon left that can be burned, after which we will be committed to temperature rises outside those experienced by the planet for hundreds of thousands of years.

The scientists have done their job; now is the time for politicians to take a lead, and everyone to act.

Professor Chris Rapley CBE
Department of Earth Sciences
University College London
 

 

Note: The Global Ocean Commission says the IPCC report “shows that the ocean is shielding humanity from climate change impacts at significant cost to its own health”. Specifically, AR5 says:

- the upper part of the ocean is warming by about 0.1°C per decade
– the deep ocean is warming too, and will continue to do so for centuries even if emissions are curbed immediately
– sea levels are rising, currents are changing, the rapid shrinking of Arctic sea ice is freshening water around the region, and concentrations of dissolved oxygen are declining
– acidification will make up to half of the Arctic ocean uninhabitable for shelled animals by 2050.Climate News Network

The IPCC’s Fifth Assessment Report

September 27, 2013 in Antarctic, Arctic, Climate, Extreme weather, Greenhouse Gases, Greenland, Permafrost, Polar ice, Science, Sea level rise, Warming

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Vatnajökull in Iceland: The IPCC says humans are the main cause of recent warming Image: Andreas Tille via Wikimedia Commons

Vatnajökull in Iceland: The IPCC says humans are the main cause of recent warming
Image: Andreas Tille via Wikimedia Commons

By the editors

Summary for Policymakers of the Working Group I contribution to the Fifth Assessment Report

A note from the Climate News Network editors: we have prepared this very abbreviated version of the first instalment of the IPCC’s Fifth Assessment Report (AR5) to serve as an objective guide to some of the headline issues it covers. It is in no sense an evaluation of what the Summary says: the wording is that of the IPCC authors themselves, except for a few cases where we have added headings. The AR5 uses a different basis as input to models from that used in its 2007 predecessor, AR4: instead of emissions scenarios, it speaks of RCPs, representative concentration pathways. So it is not possible everywhere to make a direct comparison between AR4 and AR5, though the text does so in some cases, and at the end we provide a very short list of the two reports’ conclusions on several key issues. The language of science can be complex. What follows is the IPCC scientists’ language. In the following days and weeks we will be reporting in more detail on some of their findings.

In this Summary for Policymakers, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium, or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high, and very high, and typeset in italics, e.g., medium confidence. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence. In this Summary the following terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90–100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely likely: 95–100%, more likely than not >50–100%, and extremely unlikely 0–5%) may also be used when appropriate.

Observed Changes in the Climate System

 

Atmosphere

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.

For the longest period when calculation of regional trends is sufficiently complete (1901–2012), almost the entire globe has experienced surface warming.

In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability. Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.

As one example, the rate of warming over the past 15 years, which begins with a strong El Niño, is smaller than the rate calculated since 1951.

Changes in many extreme weather and climate events have been observed since about 1950. It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale

Ocean

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence ). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971–2010. Since AR4, instrumental biases in upper-ocean temperature records have been identified and reduced, enhancing confidence in the assessment of change.

It is likely that the ocean warmed between 700 and 2000 m from 1957 to 2009. Sufficient observations are available for the period 1992 to 2005 for a global assessment of temperature change below 2000 m. There were likely no significant observed temperature trends between 2000 and 3000 m for this period. It is likely that the ocean warmed from 3000 m to the bottom for this period, with the largest warming observed in the Southern Ocean.

More than 60% of the net energy increase in the climate system is stored in the upper ocean (0–700 m) during the relatively well-sampled 40-year period from 1971 to 2010, and about 30% is stored in the ocean below 700 m. The increase in upper ocean heat content during this time period estimated from a linear trend is likely.

Cryosphere

Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence).

The average rate of ice loss from the Greenland ice sheet has very likely substantially increased … over the period 1992–2001. The average rate of ice loss from the Antarctic ice sheet has likely increased … over the period 1992–2001. There is very high confidence that these losses are mainly from the northern Antarctic Peninsula and the Amundsen Sea sector of West Antarctica.

There is high confidence that permafrost temperatures have increased in most regions since the early 1980s. Observed warming was up to 3°C in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2°C in parts of the Russian European North (1971–2010). In the latter region, a considerable reduction in permafrost thickness and areal extent has been observed over the period 1975–2005 (medium confidence).

Multiple lines of evidence support very substantial Arctic warming since the mid-20th century.

Sea Level

The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.

Since the early 1970s, glacier mass loss and ocean thermal expansion from warming together explain about 75% of the observed global mean sea level rise (high confidence). Over the period 1993–2010, global mean sea level rise is, with high confidence, consistent with the sum of the observed contributions from ocean thermal expansion due to warming, from changes in glaciers, Greenland ice sheet, Antarctic ice sheet, and land water storage.

Carbon and Other Biogeochemical Cycles

The atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification

From 1750 to 2011, CO2 emissions from fossil fuel combustion and cement production have released 365 [335 to 395] GtC [gigatonnes - one gigatonne equals 1,000,000,000 metric tonnes] to the atmosphere, while deforestation and other land use change are estimated to have released 180 [100 to 260] GtC.

Of these cumulative anthropogenic CO2 emissions, 240 [230 to 250] GtC have accumulated in the atmosphere, 155 [125 to 185] GtC have been taken up by the ocean and 150 [60 to 240] GtC have accumulated in natural terrestrial ecosystems.

Drivers of Climate Change

The total natural RF [radiative forcing - the difference between the energy received by the Earth and that which it radiates back into space] from solar irradiance changes and stratospheric volcanic aerosols made only a small contribution to the net radiative forcing throughout the last century, except for brief periods after large volcanic eruptions.

Understanding the Climate System and its Recent Changes

Compared to AR4, more detailed and longer observations and improved climate models now enable the attribution of a human contribution to detected changes in more climate system components.

Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.

Evaluation of Climate Models

Climate models have improved since the AR4. Models reproduce observed continental-scale surface temperature patterns and trends over many decades, including the more rapid warming since the mid-20th century and the cooling immediately following large volcanic eruptions (very high confidence).

The long-term climate model simulations show a trend in global-mean surface temperature
from 1951 to 2012 that agrees with the observed trend (very high confidence). There are, however, differences between simulated and observed trends over periods as short as 10 to 15 years (e.g., 1998 to 2012).

The observed reduction in surface warming trend over the period 1998–2012 as compared to the period 1951–2012, is due in roughly equal measure to a reduced trend in radiative forcing and a cooling contribution from internal variability, which includes a possible redistribution of heat within the ocean (medium confidence). The reduced trend in radiative forcing is primarily due to volcanic eruptions and the timing of the downward phase of the 11-year solar cycle.

Climate models now include more cloud and aerosol processes, and their interactions, than at the time of the AR4, but there remains low confidence in the representation and quantification of these processes in models.

The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales. It is defined as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration.

Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence). The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment reflects improved understanding, the extended temperature record in the atmosphere and ocean, and
new estimates of radiative forcing.

Detection and Attribution of Climate Change

Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.

It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.

Future Global and Regional Climate Change

Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.

The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation.

It is very likely that the Arctic sea ice cover will continue to shrink and thin and that Northern Hemisphere spring snow cover will decrease during the 21st century as global mean surface temperature rises. Global glacier volume will further decrease.

Global mean sea level will continue to rise during the 21st century. Under all RCP scenarios the rate of sea level rise will very likely exceed that observed during 1971–2010 due to increased ocean warming and increased loss of mass from glaciers and ice sheets.

Sea level rise will not be uniform. By the end of the 21st century, it is very likely that sea level will rise in more than about 95% of the ocean area. About 70% of the coastlines worldwide are projected to experience sea level change within 20% of the global mean sea level change.

Climate change will affect carbon cycle processes in a way that will exacerbate the increase of CO2 in the atmosphere (high confidence). Further uptake of carbon by the ocean will increase ocean acidification.

Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO2.

A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period.

Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Depending on the scenario, about 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1,000 years.

Sustained mass loss by ice sheets would cause larger sea level rise, and some part of the mass loss might be irreversible. There is high confidence that sustained warming greater than some threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a global mean sea level rise of up to 7 m.

Current estimates indicate that the threshold is greater than about 1°C (low confidence) but less than about 4°C (medium confidence) global mean warming with respect to pre-industrial. Abrupt and irreversible ice loss from a potential instability of marine-based sectors of the Antarctic Ice Sheet in response to climate forcing is possible, but current evidence and understanding is insufficient to make a quantitative assessment.

Methods that aim to deliberately alter the climate system to counter climate change, termed geoengineering, have been proposed. Limited evidence precludes a comprehensive quantitative assessment of both Solar Radiation Management (SRM) and Carbon Dioxide Removal (CDR) and their impact on the climate system.

CDR methods have biogeochemical and technological limitations to their potential on a global scale. There is insufficient knowledge to quantify how much CO2 emissions could be partially offset by CDR on a century timescale.

Modelling indicates that SRM methods, if realizable, have the potential to substantially offset a global temperature rise, but they would also modify the global water cycle, and would not reduce ocean acidification.

If SRM were terminated for any reason, there is high confidence that global surface temperatures would rise very rapidly to values consistent with the greenhouse gas forcing. CDR and SRM methods carry side effects and long-term consequences on a global scale.

Then and Now

For comparison, here are the IPCC’s projections in four key areas: from the 2013 AR5, in bold – from the 2007 AR4, in regular type

Probable temperature rise by 2100: 1.5-4°C under most scenarios – from 1.8-4°C
Sea level rise: very likely faster than between 1971 and 2010 – by 28-43 cm
Arctic summer sea ice disappears: very likely it will continue to shrink and thin – in second half of century
Increase in heat waves: very likely to occur more frequently and last longer – increase very likely

Antarctic ice shelves melt from below

September 15, 2013 in Antarctic, Climate, Polar ice, Sea level rise

EMBARGOED until 1700 GMT on Sunday 15 September

The calving front of the Filchner ice shelf, Antarctica Image by courtesy of Jonathan Bamber

The calving front of the Filchner ice shelf, Antarctica
Image by courtesy of Jonathan Bamber

By Alex Kirby

Scientists have discovered that many Antarctic ice shelves are losing ice not just by calving icebergs but by melting from their undersides as well.

LONDON, 15 September – There’s much more of an iceberg under the water than above it. And, it turns out, there’s much more happening beneath the surface to Antarctic ice shelves than anyone had guessed.

A team of researchers from British, Dutch and US universities has found that more ice leaves Antarctica by melting from the underside of submerged ice shelves than was previously thought, accounting for as much as 90% of the ice lost in some areas.

Iceberg production and melting results in 2,800 cubic kilometres of ice leaving the Antarctic ice sheet annually. Most is replaced by snow falling on the continent, but any imbalance means a change in global sea level.

Scientists have believed for decades that the main way this loss occurred was through iceberg calving, as huge chunks of ice broke off at the edge of a glacier.

But the team, led by academics at the University of Bristol, UK, with colleagues from Utrecht University in the Netherlands and the University of California, has used satellite and climate model data to prove that the melting of the shelves’ undersides has as large an impact as iceberg calving for Antarctica as a whole, and for some areas is far more important.

The findings, published in the journal Nature, are crucial to understanding how the ice sheet interacts with the rest of the climate system, particularly the ocean.

During the last decade the Antarctic ice sheet has been losing an increasing amount of volume. The annual turnover of ice equals 700 times the UK’s yearly domestic water usage of just four cubic kilometres a year.

The researchers found that, for some ice shelves, melting of their underbellies could account for as much as 90% of the mass loss, while for others it was only 10%.

“Understanding how the largest ice mass on the planet loses ice to the oceans is one of the most fundamental things we need to know for Antarctica.”

Ice shelves which are thinning already were identified as losing most of their mass from this type of melting, a finding which will help to show which shelves may be particularly vulnerable to changes in future ocean warming.

The scientists used satellite and airborne data to accurately measure the flow of the ice, its elevation and its thickness. These observations were combined with the output of a climate model for snowfall over the ice sheet.

The team then worked out how much ice was leaving Antarctica, either by entering the ocean from the underside of the ice shelves or by calving off the glaciers’ edges. By combining these totals they could estimate the mass loss of ice from the continent.

Professor Jonathan Bamber, from the University of Bristol’s School of Geographical Sciences, said: “Understanding how the largest ice mass on the planet loses ice to the oceans is one of the most fundamental things we need to know for Antarctica. Until recently, we assumed that most of the ice was lost through icebergs.

“Now we realise that melting underneath the ice shelves by the ocean is equally important and, for some places, far more important. This knowledge is crucial for understanding how the ice sheets interact now, and in the future, with changes in climate.”

The research was funded by a European Union programme called ice2sea and a project funded by the UK’s Natural Emvironment Research Council, Resolving Antarctic mass TrEnds (RATES). – Climate News Network

Poll pinpoints public’s climate fears

September 5, 2013 in Business, Climate, Extreme weather, Flooding, Sea level rise, Weather

FOR IMMEDIATE RELEASE

A house on Staten Island, New York City, is left destroyed by Hurricane Sandy Image: Thomas Good

Taking a hit: one of the many houses on Staten Island, New York City, devastated by Hurricane Sandy
Image: Thomas Good

By Kieran Cooke

High public anxiety about the effects of climate change features prominently in a multinational insurance group’s global survey – with 84% of people polled saying they expect more natural disasters in future

LONDON, 5 September - A worldwide survey commissioned by the multinational insurance group Swiss Re to assess public attitudes towards risk has shown that climate change is ranked high on the list of people’s concerns.

The survey, conducted on behalf of Swiss Re by the Gallup polling organisation, involved 22,000 people aged 15 and above across five continents. People were asked what concerns them most − whether it’s the economy, ageing, climate change, natural disasters, energy issues or questions about food supplies.

While almost all respondents expressed fears about the economic future in their countries, concern about climate change and natural disasters was also widespread, with 84% of respondents anticipating climate change being responsible for more natural disasters in the future.

Feel threatened

Swiss Re says a majority of respondents also said they feel threatened by the risk that climate change poses to their communities. Most said they would be willing to shoulder some of the financial burden of dealing with future risks, but felt that governments should do more to meet the challenges of climate change.

The policy of governments does not fully address the risks faced today and by future generations, respondents said. In particular, more than 90% of those surveyed want to see governments doing more to ensure more efficient energy use.

“These findings show that individuals are willing to take as much responsibility as their leaders,” says David Cole, Chief Risk Officer at Swiss Re, which commissioned the survey to mark the company’s 150th anniversary.

“The findings are a call for better co-operation between government and the private sector. It’s vital to prepare systematically for the future and make societies more resilient. That’s where Swiss Re also plays a key role with its risk expertise.”

Large insurance companies such as Swiss Re are deeply involved in assessing the economic costs associated with changes in climate, insuring against a wide range of climate-related events that include flooding, storm damage, drought, and crop failure.

Hurricane Sandy, which hit the Caribbean region and the east coast of the US in October last year, is estimated to have caused $19bn worth of damage in New York City alone.

The US accounts for a large slice of the world’s insurance market. Aon Benfield, a global reinsurance group, estimates that the cost of Hurricane Sandy, combined with losses incurred by the serious drought in the states of the Midwest in 2012, reached $100bn – a figure representing more than 65% of total worldwide insured losses last year.

Gargantuan sums

With such gargantuan sums involved, it is little wonder that insurance companies – and their shareholders – are acutely aware of the financial risks posed by climate change. Earlier this year,shareholders of insurance companies in parts of the US successfully lobbied for insurers to reveal the extent of their preparedness for events related to climate change.

Later this month, the Intergovernmental Panel on Climate Change (IPCC) is due to release the first parts of its latest assessment report. Insurance companies are sure to focus special attention on the IPCC’s likely scenarios for sea level rise – and the estimates of costs involved, particularly to coastal cities.

A recent World Bank study suggested that, by 2050, costs related to flooding brought about by a combination of sea level rise and extremes of heat, windstorms and rain in the world’s coastal cities could rise to $1 trillion per year. Flood damage in just four cities – New Orleans, New York and Miami in the US, and Guangzhou in southern China – would account for nearly half of that sum. – Climate News Network