Tag Archives: Oceans

Acidic seas block fishes’ survival mechanism

Sharks such as the smooth dogfish face a new man-made threat Image: NOAA via Wikimedia Commons
Climate of concern: sharks such as the smooth dogfish face a new man-made threat
Image: NOAA via Wikimedia Commons

By Tim Radford

Scientific studies show that the sense of smell so vital for the survival of predators such as sharks, as well as for their prey, is being impaired as carbon dioxide increases acidification of oceans.

LONDON, 18 September, 2014 − Global warming could be bad for sharks, too. These ocean-going creatures that have survived 420 million years of natural climate change could be at risk from increasingly acidic seas, according to two entirely different scientific studies.

The sharks are already in trouble everywhere. They are pursued as food or feared as a threat, and the habitat they favour is gradually being degraded or destroyed.

But Danielle Dixson, a marine conservation biologist at the Georgia Institute of Technology in the US, and colleagues report in Global Change Biology that changes in the pH value of water – in other words, as the seas became more acidic – have interfered with a shark’s ability to smell food.

Behaviour change

Dr Dixson has already shown that increasing acidification, due to greater levels of carbon dioxide in the atmosphere, could change the behaviour of reef fish, seemingly making them less afraid of predators because the acidic waters disrupt a specific receptor in the fish’s nervous system.

This time, she experimented with a shark known as the smooth dogfish (Mustelus canis), which is found in the Atlantic waters off the US coast. She tested 24 sharks in a 10-metre tank with two currents or plumes of water. One was normal sea water, and the other was rich in the odour of squid. As expected, the sharks showed a distinct preference for the smell of food.

Then she and her colleagues enriched the water with carbon dioxide − to levels predicted for mid-century as greenhouse emissions continue to rise, and the seas become more rich in carbonic acid.

When released into the most acidic water, the sharks actually avoided the plume of squid odour. Once again, the change in the water’s pH seemed to have disrupted an all-important receptor, and thus the sharks’ interest in hunting.

“Sharks are like swimming noses, so chemical cues are really important for them in finding food,” Dr Dixson said.

Less aggressive

Overall activity did not change significantly, but shark attack behaviour did. The squid odour was pumped through bricks to give the sharks something to push against, but the sharks in the most acidic waters responded less aggressively.

“They significantly reduced their bumps and bites on the bricks, compared to the control group,” Dr Dixson said. “It’s like they’re uninterested in their food.”

There is always the chance that, as acidity levels slowly rise, sharks will adjust or adapt. But increasing acidification may not even give them the chance to adapt.

In a second paper, this time in the Proceedings of the Royal Society, Rui Rosa, senior researcher at the Centre for Oceanography in Cascais, Portugal, and colleagues considered the impact of warmer and more acidic seas on the survival of the newly-hatched tropical bamboo shark (Chiloscyllium punctatum), normally found in the intertidal zones of the western Pacific.

The researchers tested hatchlings in tanks at temperatures and pH values predicted for 2100, and found “significant impairment” in survival rates.

In their experiments at normal temperature conditions, mortality among the hatchlings was zero. In experimental conditions, behaviour changes were apparent from the outset and, within 30 days, more than 40% had died. – Climate News Network

Ocean acidification and GHGs hit record levels

Reef grief: corals, fisheries and tourism will all be damaged by  ocean acidification Image: Ritiks via Wikimedia Commons
Reef stricken: corals, fisheries and tourism will all be damaged by ocean acidification
Image: Ritiks via Wikimedia Commons

By Alex Kirby

New scientific evidence of the highest greenhouse gas concentrations on record is compounded by the revelation that oceans are acidifying faster than at any time in the last 300 million years.

LONDON, 9 September, 2014 – The World Meteorological Organisation (WMO) reports that the amounts of atmospheric greenhouse gases reached a new high in 2013, driven by rapidly rising levels of carbon dioxide.

The news is consistent with trends in fossil fuel consumption. But what comes as more of a surprise is the WMO’s revelation that the current rate of ocean acidification, which greenhouse gases (GHGs) help to cause, appears unprecedented in at least the last 300 million years.

The details of growing GHG levels are in the annual Greenhouse Gas Bulletin, published by the WMO – the United Nations specialist agency that plays a leading role in international efforts to monitor and protect the environment.

They show that between 1990 and 2013 there was a 34% increase in radiative forcing – the warming effect on our climate – because of long-lived greenhouse gases such as carbon dioxide (CO2), methane and nitrous oxide.

Complex interactions

The Bulletin reports on atmospheric concentrations – not emissions − of greenhouse gases. Emissions are what go into the atmosphere, while concentrations are what stay there after the complex system of interactions between the atmosphere, biosphere (the entire global ecological system) and the oceans.

About a quarter of total emissions are taken up by the oceans and another quarter by the biosphere, cutting levels of atmospheric CO2.

In 2013, the atmospheric concentration of CO2 was 142% higher than before the Industrial Revolution started, in about 1750. Concentrations of methane and nitrous oxide had risen by 253% and 121% respectively.

The observations from WMO’s Global Atmosphere Watch network showed that CO2 levels increased more from 2012 to 2013 than during any other year since 1984. Scientists think this may be related to reduced CO2 absorption by the Earth’s biosphere, as well as by the steady increase in emissions.

Although the oceans lessen the increase in CO2 that would otherwise happen in the atmosphere, they do so at a price to marine life and to fishing communities − and also to tourism. The Bulletin says the oceans appear to be acidifying faster than at any time in at least the last 300 million years.

“We know without any doubt that our climate is changing and our weather is becoming more extreme due to human activities such as the burning of fossil fuels,” said the WMO’s secretary-general, Michel Jarraud.

“We are running out of time. The laws
of physics are non-negotiable.”

“The Greenhouse Gas Bulletin shows that, far from falling, the concentration of carbon dioxide in the atmosphere actually increased last year at the fastest rate for nearly 30 years. We are running out of time. The laws of physics are non-negotiable.

“The Bulletin provides a scientific base for decision-making. We have the knowledge and we have the tools for action to try to keep temperature increases within 2°C to give our planet a chance and to give our children and grandchildren a future. Pleading ignorance can no longer be an excuse for not acting.”

Wendy Watson-Wright, executive secretary of the Intergovernmental Oceanographic Commission of UNESCO, said: “It is high time the ocean, as the primary driver of the planet’s climate and attenuator of climate change, becomes a central part of climate change discussions.

“If global warming is not a strong enough reason to cut CO2 emissions, ocean acidification should be, since its effects are already being felt and will increase for many decades to come.”

The amount of CO2 in the atmosphere reached 396.0 parts per million (ppm) in 2013. At the current rate of increase, the global annual average concentration is set to cross the symbolic 400 ppm threshold within the next two years.

More potent

Methane, in the short term, is a far more powerful greenhouse gas than CO2 − 34 times more potent over a century, but 84 times more over 20 years.

Atmospheric methane reached a new high of about 1,824 parts per billion (ppb) in 2013, because of increased emissions from human sources. Since 2007, it has started increasing again, after a temporary period of levelling-off.

Nitrous oxide’s atmospheric concentration in 2013 was about 325.9 ppb. Its impact on climate, over a century, is 298 times greater than equal emissions of CO2. It also plays an important role in the destruction of the ozone layer that protects the Earth from harmful ultraviolet solar radiation.

The oceans currently absorb a quarter of anthropogenic CO2 emissions − about 4kg of CO2 per day per person. Acidification will continue to accelerate at least until mid-century, according to projections from Earth system models. − Climate News Network

Bluefin tuna follow prey to warming high Arctic

Large bluefin tuna that were caught among mackerel near Greenland Image: Greenland Fisheries License Control Authority
Large bluefin tuna that were caught among mackerel near Greenland
Image: Greenland Fisheries License Control Authority

By Alex Kirby

A research ship’s surprise catch of bluefin tuna further north than ever recorded indicates that climate change is restructuring the food web as the waters of east Greenland get warmer.

LONDON, 8 September, 2014 − Biologists and fishermen aboard a scientific cruise in the Arctic while they investigated mackerel stocks caught more than they bargained for − three large bluefin tuna, each weighing about 100 kilograms.

The research ship was sailing through the Denmark Strait, which separates Greenland from Iceland. Bluefin tuna are very seldom found near Greenland, and there are no other scientific reports of them venturing that far north. The most recent report of a tuna anywhere near was a stranding in 1900, a long way south at Qaqortoq, on the south-western tip of Greenland.

Details of the find, during a cruise in August 2012 organised by the Center for Macroecology, Evolution and Climate at the University of Copenhagen, have now been published in the journal Global Change Biology.

Expanded range

The lead author, Professor Brian MacKenzie, said bluefin tuna usually search for prey in areas where surface temperatures are warmer than 11°C.

At the time of the catch, the Denmark Strait was unusually warm, and one of tuna’s preferred prey species, mackerel, had already expanded their range into the region.

Professor MacKenzie and his colleagues write: “Regional temperatures in August 2012 were historically high and contributed to a warming trend since 1985, when temperatures began to rise.

“The presence of bluefin tuna in this region is likely due to a combination of warm temperatures . . . and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.”

They say their data was too limited to estimate how many tuna came so far north, but because bluefins are a schooling species − with schools having from 10 to 100 individuals − and because the three tuna were caught in the same haul, it is likely there were many more present.

The report says: “Satellite imagery showing the spread of warm water from the south-east towards east Greenland suggests that recent warming and climate change may have opened a migration pathway from the European shelf towards Greenland for migratory species.”

It acknowledges that the fish may have swum to the Denmark Strait from the north-west Atlantic, and concludes: “Our results show that rising temperatures have been progressively leading a . . . trophic [high in the food chain] cascade into east Greenland waters via improved thermal conditions for migratory prey and predator species.”

New fishing quotas

Nobody knows why bluefin tuna disappeared from the waters near Denmark and in the Norwegian Sea during the 1960s, nor when they might return. But Iceland and Norway have been allocated new fishing quotas of 30 tonnes each for the species in 2014.

An adult bluefin tuna is typically 1.5m-2m long, but some have been as big as 4.5m and weighed 650 kg. The fish are highly prized for sushi, especially in Japan.

Further climate-related changes in distributions of commercial fish such as mackerel and herring will mean new fishery and ecosystem management plans are going to be needed, says the report’s co-author, Helle Siegstad, head of the Department for Fish and Shellfish at the Greenland Institute of Natural Resources.

The Denmark Strait tuna will be discussed at the annual science conference of the International Council for the Exploration of the Sea (ICES), which starts on 15 September in the Spanish coastal city of A Coruña. – Climate News Network

Fresh water causes Antarctic seas to rise faster

Meltwater from Antarctic glaciers is causing sea levels to rise Image Jason Auch via Wikimedia Commons
Glacial meltwater is a key factor in the sea level rise in Antarctica
Image Jason Auch via Wikimedia Commons

By Tim Radford

Researchers in the UK have established that billions of tonnes of fresh water from melting glaciers are causing Antarctic sea levels to rise much higher and faster than the global average.

LONDON, 7 September, 2014 − Sea levels around Antarctica are rising faster than anywhere else in the southern ocean. The global average rise in ocean heights in the last 19 years has been 6cms, but the rise in seas around Antarctica is 2cms higher.

This seemingly counter-intuitive finding is certainly a consequence of melting ice in the Southern Ocean, but the connection with global warming is, for the moment, tenuous. The agency that is behind the rising sea levels is simply an excess of fresh water from melting glaciers − about 350 billion tonnes of it.

“Fresh water is less dense than salt water, and so in regions where an excess of fresh water has accumulated we expect a localised rise in sea level,” says Craig Rye, an oceanography researcher at of the University of Southampton in the UK, who, with colleagues, has published the findings in Nature Geoscience.

Partly because the oceans are warmer and are therefore expanding, and partly because the terrestrial glaciers are in retreat, global sea levels on average have crept up by about 3 millimetres a year. Waters off the Antarctic shelf seem to be gaining an additional 2mm a year.

Less saline

The scientists studied satellite scans of a region of more than a million square kilometres to make their finding, and used ship-based studies of the Antarctic sea water to confirm that is has become less saline.

The melting of the Antarctic ice sheet – German scientists recently calculated that around 125 cubic kilometres of meltwater is running off the continent each year − and the thinning of the floating ice shelves is enough to explain the unexpected rise.

Computer model studies confirm the interpretation that the rise is happening because the southern seas have just got fresher. The consequences in the longer term are uncertain.

Rye, a postgraduate researcher, said: “The interaction between air, sea and ice in these seas is central to the stability of the Antarctic ice sheet and global sea levels, as well as other environmental processes, such as the generation of Antarctic bottom water, which cools and ventilates much of the global ocean abyss.” – Climate News Network

Pre-history proof of climate’s see-saw sensitivity

The woolly rhinoceros once roamed wild on the plains of Europe Image: Public Library of Science via Wikimedia Commons
The woolly rhinoceros once roamed wild on the plains of Europe
Image: Public Library of Science via Wikimedia Commons

By Tim Radford

Computer simulations reaching back deep into the last Ice Age have enabled scientists to put a historic perspective on how even small variations in the climate system can lead to dramatic temperature change.

LONDON, 24 August, 2014 − It doesn’t take much to change a planet’s climate – just a little shift in the Northern hemisphere glacial ice sheet and a bit more carbon dioxide in the atmosphere. After that, the response is rapid. The tropical rain belt moves north and the southern hemisphere cools a bit, in some sort of bipolar see-saw response.

Sound familiar? It does, and it doesn’t. It all happened long before the internal combustion engine, or even the new Stone Age.

Researchers from the Alfred Wegener Institute’s Helmholtz Centre for Polar and Marine Research, Bremerhaven, the University of Bremen, Germany, and the University of Cardiff in the UK, report in Nature journal that they have made climate simulations that agree with observations of historical climate change that date back 800,000 years.

Long before the present alarms about global warming through the emission of carbon dioxide from fossil fuels, climate researchers were puzzled by the phenomenon of the Ice Ages and the “interglacials” that punctuated those long periods when the Arctic ice extended from the North Pole to the Atlantic coast of France, and over huge tracts of North America.

Vanished species

Mysteriously, and at great speed, the temperatures would rise by up to 10°C and the vast walls of ice would retreat. Lion, hyena and rhinoceros would invade the wild plains of what is now southern England, and now-vanished species of humans would hunt big game and gather fruit and seeds in the valleys and forests of Europe and America.

Since the end 10,000 years ago of the last ice age – itself a very rapid event – was the springboard for agriculture and civilisation, and eventually an Industrial Revolution based on fossil fuels, the story of climate change plays a powerful role in human history.

So any analysis of the tiny shifts in ice cover that seemed to trigger these dramatic, bygone events can be helpful in understanding the long story of the making of the modern world.

The researchers found a tentative scenario involving weak ocean currents, and prevailing winds that shifted the sea ice and allowed the oceans and atmosphere to exchange heat, pushing warmer water into the north-east Atlantic.

These changes precipitated a dramatic warming of the northern hemisphere in just a few decades, and the retreat of the glaciers for an extended period before the ice returned to claim much of the landmass again. But, overall, such changes tended to occur when sea levels reached a certain height.

“The rapid climate changes known in the scientific world as Dansgaard-Oeschger events were limited to a period of time from 110,000 to 23,000 years before the present,” said Xu Zhang, the report’s lead author.

“The abrupt climate changes did not take place at the extreme low sea levels, corresponding to the time of maximum glaciations 20,000 years ago, or at high sea levels such as those prevailing today. They occurred during periods of intermediate ice volume and intermediate sea levels”

Climate swings

Co-author Gerrit Lohmann, who leads the Wegener Institute’s palaeoclimate dynamics group, said: “Using the simulations performed with our climate model, we were able to demonstrate that the climate system can respond to small changes with abrupt climate swings.

“At medium sea levels, powerful forces − such as the dramatic acceleration of polar ice cap melting − are not necessary to result in abrupt climate shifts and associated drastic temperature changes.”

How much this tells anybody about modern climate change is open to debate. Right now, according to this line of evidence, the planet’s climate could be in one of its more stable phases of the Earth’s history.

But while the conditions for the kind of rapid change recorded in pre-history do not exist today, Prof Lohmann warns that “sudden climate changes cannot be excluded in the future”. – Climate News Network

Atlantic depths may hold key to heat hiatus

A jellyfish floats just above the seafloor of the deep Atlantic Image: NOAA/OAR/OER via Wikimedia Commons
A jellyfish floats just above the seafloor of the deep Atlantic Ocean
Image: NOAA/OAR/OER via Wikimedia Commons

By Tim Radford

Researchers analysing millions of oceanographic measurements believe they may finally have got to the bottom of the conundrum about why there is a slowdown in global warming despite greenhouse gas emissions rising.

LONDON, 22 August, 2014 − For years, researchers have puzzled over the temperature rises that haven’t happened – but scientists in China and the US believe they have cracked the mystery of the missing heat.

While calculations indicate that global average temperatures should be rising predictably, the planetary thermometers tell a different story.

But now Xianyao Chen, an oceanographer at the Ocean University of China in Qingdao, and Ka-Kit Tung, an atmospheric scientist at the University of Washington in Seattle, report in Science journal that they think they know where the notional extra heat has gone. It is at the bottom of the Atlantic Ocean.

And this time their conclusion isn’t based only on mathematical models and computer simulations. In their research − funded by the US National Science Foundation and the National Natural Science Foundation of China – they analysed millions of measurements of temperature and salinity taken by oceanographic instruments since 1970, and tracked the pathways that the heat must have taken since the beginning of the 21st century.

High temperatures

But first, a restatement of the conundrum. For more than a century, climate scientists have known that higher levels of carbon dioxide in the atmosphere mean higher atmospheric temperatures. For more than 30 years, every investigation has confirmed this link. And for the last 30 years of the 20th century, as greenhouse gas emissions increased, so did average temperatures.

This rise has continued, with 13 of the 14 warmest years ever recorded all falling in the 21st century, but the rate of increase unexpectedly slowed.

Researchers had expected that there would be some sort of heat hiatus, but not during the first years of the century, and they have been scratching their heads and examining the data again.

Some think that the measurements may be incomplete, or that natural cycles, such as the Pacific cooling event called La Niña, may be at play. Some have suggested that the pattern of trade winds may have a role in taking the warmth into the deep ocean, and some have suspected all along that the heat could be found far below the oceanic surface.

In the same week as the publication in Science, Reto  Knutti, a climate physicist at the federal technology institute ETH Zurich, and his colleague, Markus Huber, reported in Nature Geoscience that the apparent slowdown could be attributed to a cocktail of causes: a longer period of weaker solar irradiance – the sun has its own cycles of intensity − and to the cycle of El Niño and La Niña weather phenomena in the Pacific, and also to incompletely measured data.

“Many of the earlier papers had focused on
symptoms at the surface of the Earth”

But the Science report authors think they have an in-depth solution. “Every week, there’s a new explanation of the hiatus,” said Ka-Kit Tung. “Many of the earlier papers had focused on symptoms at the surface of the Earth, where we see many different and related phenomena. We looked at observations in the ocean to try to find an underlying cause.”

The oceans cover 70% of the planet, and are capable of storing 90% of the planet’s heat content. So the two Science report authors argue that a sudden shift in ocean salinity that corresponded with the slowdown of global warming could have triggered the movement of the heat to much deeper waters.

Saltier water is denser, sinks faster, and takes surface heat with it. As the two scientists see it, the depths of the North and South Atlantic have absorbed more heat in the last 14 years than the rest of the global ocean system put together.

This does not mean that global warming is not a problem: heat in the deep oceans is likely to come back to the surface, and to the atmosphere, sooner or later.

Natural cycle

The changes in the Atlantic ocean circulation system are part of a natural cycle that seems to date back many centuries. The surprise discovery by Chen and Tung is that the heat is tucked away in the Atlantic and Southern Oceans, rather than the Pacific − the suspected hiding place until now.

The argument is a complex one, and the latest research probably hasn’t settled the matter.

“All these analyses of ocean heat content are interpreting small changes in ocean temperature, and it will need to be picked over and repeated by others before being fully accepted,” said Professor Andrew Watson, head of the Marine and Atmospheric Science group at the University of Exeter, UK.

And Piers Forster, professor of climate change at the University of Leeds in the UK, said: “Most importantly, this paper is another nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down.

“Variability in the ocean will not affect long-term climate trends, but may mean we have a period of accelerated warming to look forward to.” – Climate News Network

Antarctic warming could accelerate sea level rise

Warming would cause more Antarctic ice to break off and melt Image: PIK/R.Winkelmann
Rising concern: warming would cause more Antarctic ice to break off and melt
Image: PIK (R.Winkelmann)

By Alex Kirby

An international study says warming is affecting not only the Arctic but also the Antarctic – and that could significantly raise global sea levels much faster than previously predicted.

LONDON, 20 August, 2014 − The effect of climate change on the world’s two polar regions looks like a stark contrast: the Arctic is warming faster than most of the rest of the Earth, while most of Antarctica appears to remain reassuringly locked in a frigid embrace.

But an international scientific team says the reality is quite different. The Antarctic is warming too, it says, and the southern ice could become the main cause of global sea level rise during this century − far sooner than previously thought.

The study, led by the Potsdam Institute for Climate Impact Research (PIK) in Germany, found that ice discharge from Antarctica could contribute up to 37 centimetres to global sea levels by 2100.

Computer simulations

The study is the first comprehensive estimate of the full range of Antarctica’s potential contribution to global sea level rise based on physical computer simulations. It combines state-of-the-art climate models and observational data with various ice models.

The results of the study − published in the European Geosciences Union’s journal, Earth System Dynamics − reproduce Antarctica’s recent contribution to sea level rise, as observed by satellites over the last two decades.

“If greenhouse gases continue to rise as before, ice discharge from Antarctica could raise the global ocean by an additional 1 to 37 centimetres this century,” says the study’s lead author, Anders Levermann, PIK professor of dynamics of the climate system.

“Science needs to be clear about the uncertainty,
so that decision-makers can consider the potential implications . . .”

“This is a big range – which is exactly why we call it a risk. Science needs to be clear about the uncertainty, so that decision-makers on the coast and in coastal mega-cities like Shanghai or New York can consider the potential implications in their planning processes.”

The scientists analysed how rising global average temperatures resulted in a warming of the ocean around Antarctica, influencing the melting of the Antarctic ice shelves.

Antarctica currently contributes less than 10% to global sea level rise and is a relatively minor player in comparison with the impact of the oceans’ increasing thermal expansion and the melting of glaciers.

But the major contributors to future long-term sea level rise are expected to be the huge volumes of ice locked up in Greenland and the Antarctic ice sheets. The marine ice sheets in West Antarctica alone could raise sea level by several metres over a period of several centuries.

The study’s computed projections for this century’s sea level contribution are significantly higher than the upper end of the latest projections by the Intergovernmental Panel on Climate Change. These suggest a probable rise by 2100 of around 60cm, although other estimates put the figure almost twice as high.

Even if governments can agree and enforce strict climate policies limiting global warming below the international target level of a maximum 2°C increase, Antarctica’s contribution to global sea level rise is expected still to range from 0 to 23cm this century.

Critical input

A co-author of the study, Robert Bindschadler, from the NASA Goddard Space Flight Center, said: “This paper is a critical input to projections of possible future contributions of diminishing ice sheets to sea level by a rigorous consideration of uncertainty of not only the results of ice sheet models themselves but also the climate and ocean forcing driving the ice sheet models.

“Billions of dollars, euros, yuan, etc, are at stake, and wise and cost-effective decision-makers require this type of useful information from the scientific experts.”

But major modeling challenges still remain. Datasets of Antarctic bedrock topography, for instance, are still inadequate, and some physical processes of interaction between ice and ocean cannot yet be sufficiently simulated.

The team also emphasises that the study’s results are limited to this century, while all 19 of the comprehensive climate models used show that the impacts of atmospheric warming on Antarctic ice shelf cavities will hit with a time delay of several decades.

However, Levermann says: “Earlier research indicated that Antarctica would become important in the long term. But pulling together all the evidence, it seems that Antarctica could become the dominant cause of sea level rise much sooner.” − Climate News Network

Climate changes ensnare Antarctic predator

Antarctic fur seals at Stromness on South Georgia island Image: Liam Quinn via Wikimedia Commons
Antarctic fur seals at Stromness on South Georgia island
Image: Liam Quinn via Wikimedia Commons

By Tim Radford

British scientists have recorded lower birth weights in female Antarctic fur seals as warming seas deplete their prime food source − but they have also observed genetic variations that could be crucial for survival.

LONDON, 29 July, 2014 − Climate change has begun to take its toll of one of Antarctica’s top predators. The Antarctic fur seal is being born with a lower weight and tends to breed later than earlier generations − almost certainly in response to the reduced availability of its prime food, krill.

But the fur seal (Arctocephalus gazelle) is also changing in other ways. British Antarctic Survey (BAS) scientists report in Nature that those females that survive to motherhood are more likely to have a higher level of genetic variation − a characteristic known as “heterozygous”, associated with higher fitness in many species.

In a world of environmental change – of warming seas and changing ocean chemistry – this confers a survival advantage, in that the individual is more likely to cope with the stresses of change.

Research such as this is based on long periods of observation, and the scientists gathered data from as far back as 1981 to assess the changes in a population of fur seals in South Georgia, in the southern Atlantic.

Genetic samples

They measured age, body length, weight, counted the numbers of sea pups, noted the diet, and recorded climate data. They also took genetic samples from 1,728 seals.

“Compared with 20 years ago, we can see that female fur seals are now born with a lower weight, those that survive and return to breed tend to be the bigger ones, and they have their first pup later in life than they used to,” said the report’s lead author, Jaume Forcada, BAS marine mammal leader.

“Such changes are typically associated with food stress. An important food source for the seals is Antarctic krill, and decades of data collected at South Georgia show how changes in the seal population have occurred over time with krill availability.

“Even if krill is very abundant, environmental variation determines its availability in the seals’ feeding grounds. This variation is driven by climate, which impacts local atmospheric, sea ice and oceanographic conditions.”

If the climatic conditions are adverse, then krill is harder to find, which makes it tough on fur seals and, directly or indirectly, all other Antarctic predators. But the picture for the moment remains uncertain.

Recently, other researchers pronounced that the population in Antarctica of the Adélie penguin – another greedy consumer of krill – is higher than all previous estimates, which suggests that some species at least are, for the moment, finding enough for supper.

But the krill population is sensitive to a south polar phenomenon called the southern annular mode (SAM), a seasonal pattern of winds and pressures that changes from time to time.

Survival fitness

The BAS team found that the seal population responded to the notorious El Niño cycle in the Pacific, and to the SAM, and that the data from this population clearly showed a response to climate change. Overall, the number of heterozygous seals has increased by 17%, but other indicators of survival fitness are not so encouraging.

“Over the last two decades, the proportion of breeding females that are highly heterozygous has increased, as these individuals are more likely to survive the changing conditions,” said the report’s co-author, Joe Hoffman, reader in population genetics at Bielefeld University, Germany.

“Strong selection by the environment can drive rapid evolution. However, in this case the seals do not appear to be evolving because surviving females do not pass their heterozygosity on to their offspring.

“Therefore, with each new generation the process of selection has to start all over again, with only those individuals that happen to be born heterozygous having a good chance of survival. As the climate continues to change, many fur seal pups are not surviving to adulthood, and the population is declining.” – Climate News Network

Data adds to confusion over polar sea ice

The expansion of Antarctic sea ice may have been overestimated. Image: Jason Auch via Wikimedia Commons
The expansion of Antarctic sea ice may have been overestimated.
Image: Jason Auch via Wikimedia Commons

By Tim Radford

Possible errors in the interpretation of satellite data may help to explain scientists’ puzzlement over indications that sea ice cover is apparently increasing in the Antarctic, but is shrinking visibly in the Arctic.

LONDON, 26 July, 2014 − Scientists believe they may have found explanations for two inconsistencies in their understanding of global warming.

One cause for head scratching is in the Antarctic, where the sea ice seems to be getting bigger when it ought to be shrinking, and another has been the apparent slowdown overall in the rate of global warming for the last decade.

Climate scientists around the world have been picking away at both puzzles, and not just because climate sceptics and energy industry lobbyists use them as ammunition to argue that global warming is not a problem at all. Scientists are naturally unhappy when data doesn’t match their predictions − and they want to know the reason why.

The Antarctic problem is hard to miss. The Arctic Ocean sea ice is shrinking visibly, and the entire sea could be ice-free most summers in a few decades. But even though there is clear evidence from separate sources that West Antarctica is responding to climate change, the southern hemisphere ice cover, overall, has been increasing.

Or has it? Ian Eisenman, a climatologist at the Scripps Institution of Oceanography at the University of California San Diego, begs to differ. He and colleagues report, in The Cryosphere journal, that it could be due to an error in the way satellite data is processed.

Spliced together

Scientists have been using satellite data to check sea ice cover for 35 years. But the data does not come from one instrument on just one satellite: observations transmitted from a series of satellites have been spliced together.

One report from the Intergovernmental Panel on Climate Change said the sea ice cover was more or less constant, but a later report said it had grown by 16,500 square kilometers a year between 1979 and 2012.

“When we looked at how the numbers reported for the trend had changed, and we looked at the time series of Antarctic sea ice, it didn’t look right,” Dr Eisenman said.

The researchers think that the difference between the two datasets might be linked to a change in satellite sensors in 1991, and the way the data collected by the two instruments was calibrated. What the Scripps team has done is identify a source of possible error, but it hasn’t settled the question one way or the other.

Since the Arctic and Antarctic are very different places, it would be unrealistic to expect the patterns of melting to be the same. And it may still be that southern hemisphere sea ice is growing.

However, while that question remains open, there is less doubt about the long slowdown in the rate of average global warming during the 21st century.

Missing heat

Separate teams of researchers have proposed a series of possible explanations for the failure of the climate to keep up with the projections of the climate scientists. These have included the suggestion that the missing heat may be “concealed” in the deep oceans, and that a pause in warming was going to happen anyway, but it just happened earlier than anyone expected.

Shaun Lovejoy, professor of physics at McGill University in Canada, reports in Geophysical Research Letters that there is yet another explanation. He argues, from statistical analysis, that coincidentally with the increase in man-made emissions of greenhouse gases, there has been a natural cycle at work, and that the most recent human impact on climate has been damped down by a cooling phase.

He had already ruled out with 99% certainty the possibility that natural variation could explain all the ups and downs of global average temperatures since 1800. This time he used the same statistical approach to the data for the 15 years from 1998 to the present.

His research suggests that there has been a natural cooling of 0.28°C to 0.37°C since 1998, which is in line with natural variations that occur every 20 to 50 years. “The pause has a convincing statistical explanation,” Lovejoy says. – Climate News Network

Hi-tech quest for Arctic sea ice answers

Walrus surfacing through sea ice off the Alaska coast Image: Joel Garlich Miller/USFWS via Wikimedia Commons
Breakthrough: walrus surfacing in sea ice off the coast of Alaska
Image: Joel Garlich Miller/USFWS via Wikimedia Commons

By Tim Radford

A sophisticated array of automatic sensors will allow scientists to conduct the longest ever monitoring programme to determine the precise physics of summer sea ice melt in the Arctic.

LONDON, 20 July, 2014 − An international team of scientists plan to spend months watching ice melt. But although it will take longer and cost a lot more than watching paint dry, it will be much more interesting and rewarding.

They plan to discover just how the Arctic ice retreats, the rate at which it melts, and the oceanographic processes at work.

The Arctic ice cap is a vital part of the climate machine, and the basis of an important ecosystem. But although the polar ice once stretched far further south, it has been both thinning and shrinking for more than three decades. This melting shows signs of accelerating, with consequences for nations far to the south, but researchers still don’t know much about the physics of the process.

Suite of technologies

So the US Naval Research Laboratory, oceanographers from France and the US, the British Antarctic Survey, the Korean Polar Research Institute, the Scottish Association for Marine Science, and the Universities of Cambridge in the UK and Yale in the US have co-ordinated a suite of technologies to monitor every detail of this summer’s ice retreat from the Alaskan shoreline, northwards.

They will use an array of floats, buoys, sensors, thermometers, tethers, GPS receivers and automated weather stations to measure every detail, such as the flow of warmer water, growth and pattern of waves, the wind speed and direction, air pressure, and humidity.

There will be buoys fixed in the ice to record both the melting and – later in the year – its refreezing, and an array of ice-tethered profilers to monitor the changes in the upper ocean. Autonomous sea gliders, too, will be released to explore below the ice shelf and report back every time they surface.

The Arctic summer ice is an example of positive feedback. Ice reflects sunlight, so it is its own insulator, and keeps itself cold. But as it melts and retreats, the exposed darker ocean waters can absorb more radiation, and bring more warmth to the edges of the retreating ice, thus accelerating the process.

It freezes again, but – on average – each year the ice cap becomes thinner, and the total area frozen continues to shrink. Researchers think they understand the big picture, but now they want the confirmatory fine detail.

Melt season

“This has never been done at this level, over such a large area and for such a long period of time,” said Craig Lee, of the University of Washington, who leads the Marginal Ice Zone Programme project. “We’re really trying to resolve the physics over the course of an entire melt season.”

The project began in March, when researchers planted an array of sensors along a line 200 miles to the north of Alaska. In August, a Korean icebreaker will install more equipment, and a team from Miami is studying high resolution satellite pictures of ice floes in the region. Biologists will also want to understand the effect of temperature changes on marine micro-organisms.

“The field programme will provide unique insight into the processes driving the summer melt of Arctic ice,” Dr Lee said. “It’s the automation and unprecedented collaboration that allows us to be out there for the entire season. You couldn’t afford to be out there at this intensity, for this length of time, any other way.” − Climate News Network