Black Sea warming linked to 2012 Russian floods

Black Sea warming linked to 2012 Russian floods

Researchers say devastating 2012 Russian flood occurred only because of global warming elsewhere.

LONDON, 30 July, 2015 – Climate scientists, ever reluctant to link any one catastrophic weather event to global warming or climate change, have taken another step nearer the establishment of direct blame.

They do not say that global warming triggered a devastating flood that swept through the Russian town of Krymsk and killed more than 150 people. But they do say the flood three years ago happened only because of decades of rising temperatures nearby.

If the surface temperatures in the Black Sea had not been rising steadily for the last 30 years, researchers report, such a flood would not have been possible.

In one of the first direct connections of this kind, Edmund Meredith of the Helmholtz Centre for Ocean Research in Kiel, Germany and colleagues spell it out.

They report in Nature Geoscience that anthropogenic warming in the Black Sea region played “a crucial role” in the extreme and unprecedented flooding that made thousands homeless, turned a town into a sea of mud, and triggered a bitter political row in Russia.

The scientists call the Krymsk floods “a showcase example” of the potential consequences of human-fuelled global warming because of rising emissions of the greenhouse gas carbon dioxide in the atmosphere in the last 200 years.

Five-metre wave

The reasoning goes like this: they looked at regional rainfall levels and found – using computer simulations – that precipitation was 300% higher on average with observed Black Sea surface temperatures, compared to simulations where the warming trend over the past 30 years was removed.

That is, the simulations showed that without past surface ocean warming, what meteorologists call deep convection – the heat-driven transport of warm, moist air to the upper atmosphere, active in thunderstorms, which often results in heavy precipitation– does not develop in the region.

What happened in July 2012 was that a cyclone moved across the Black Sea and carried moist air over to the foothills of the western Caucasus, followed by a “tongue” of saturated air over Krymsk in the form of a summer thunderstorm.

Russian officials reportedly saw the calamity coming but failed to issue a warning: a five-metre wave of water swept through a town of 57,000 people, with catastrophic consequences. The official death toll reached 172.

The Kiel researchers do not see the event as a statistical freak, but as an outcome of overall warming of the Black Sea and the Mediterranean, with the knock-on effect not just of more precipitation, but greater extremes of precipitation.

Uncertain expectations

As the great American novelist Mark Twain once observed, climate is what we expect, but weather is what we get. Because extremes are rare events, meteorologists prefer to regard them as variations that in total add up to define an average.

But as temperatures rise on average, the intensity and frequency of extremes should, on statistical reasoning, also be on the rise. Scientists have thought increasingly about the possibility of links between random events and background human activity and have warned that drought-stricken California’s vulnerability to drought is likely to increase with climate change.

But it is rare for researchers to arrive at a connection as direct as the Nature Geoscience paper that spells out the process by which a global trend drives a local tragedy.

And, very cautiously, and in very general terms, the scientists warn that such things could happen again. The climate projections, they say, promise increased sea surface temperatures and more summer cyclones in the Black Sea and Mediterranean regions.

“This suggests a corresponding increased risk of intense convective precipitation events,” they conclude. “Other coastal regions with comparable geographical features may, where similar trends are projected, be similarly affected.” – Climate News Network

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Global warming threatens colder climate for Europe

Global warming threatens colder climate for Europe

New evidence that increased melting of sea ice as the Earth warms could weaken the Gulf Stream and reduce temperatures in western Europe.

LONDON, 3 July, 2015 – Scientists have yet again warned that weakening ocean circulation in the North Atlantic could deliver a climate paradox − a colder Europe as a consequence of global warming.

A study published in Nature Climate Change found that as sea ice off Iceland and Greenland retreats, the flow of cold, dense water to the bottom of the North Atlantic ocean could be reduced, and therefore weaken the warming effects of the Gulf Stream.

The great submarine current − sometimes called the Atlantic Conveyor − flows south to surface in the tropics as the Gulf Stream, which then flows north again to deliver tropic warmth to European coasts.

However, a slowdown in the natural overturning of the ocean could weaken the Gulf Stream, which in turn could cool the atmosphere over the British Isles and western Europe.

“A warm western Europe requires a cold North Atlantic, and the warming that the North Atlantic is now experiencing has the potential to result in a cooling over Western Europe,” says Kent Moore, a professor of physics at the University of Toronto Mississauga, Canada.

Calamitous change

Such a possible collapse of a natural oceanic system is predicated as one of the irreversible tipping points that could result in calamitous climate change.

Scientists have twice warned in the past six months that such change could be irreversible, unless governments jointly decide to dramatically reduce greenhouse gas emissions from the combustion of fossil fuels by switching to renewable sources of energy.

Another research group reported in March this year on how the changing salinity of the northern ocean waters − because of the increasing flow of meltwater from land-borne glaciers − threatened a weakening of the Atlantic Conveyor.

“The heat exchange is weaker – it’s like turning down the stove 20%”

In the latest study, Professor Moore and colleagues from Norway, the US and the UK looked not at changes in ocean salinity, but at the exchange of heat between sea and air.

Climate is driven by contrasts, and the flow of heat between water and wind in winter has weakened by around 20% since 1979. The Arctic is the fastest-warming region of the planet, and changes in the polar climate can have dramatic consequences for the temperate zones.

Prof Moore and his colleagues looked at wintertime data from the Iceland and Greenland Seas between 1958 and 2014, then used computer simulations to model potential changes to the Conveyor − more formally known to oceanographers and climate scientists as the Atlantic Meridional Ocean Circulation.

Cold and salty

The warm current loses its heat to the atmosphere as it moves north, and water that is both cold and salty is denser and more likely to descend.

The most effective place for such a process to happen is at the edge of the sea ice. If the sea ice retreats, then so does the region of maximum heat exchange. For the past 10,000 years or so, this heat exchange has happened at the ideal spot for surface waters to sink. Any change might not be for the better.

The Gulf Stream is the agency that makes Britain, for example, about 5°C warmer than Labrador in Canada, on the same latitude. A British government chief scientific adviser once calculated that the Gulf Stream delivered the warmth of 27,000 power stations. So if it weakens, Europe could start to feel the chill.

“The heat exchange is weaker – it’s like turning down the stove 20%,” Prof Moore says. “We believe the weakening will continue and eventually cause changes in the Atlantic Meridional Overturning Circulation and the Gulf Stream, which can impact the climate of Europe.” – Climate News Network

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Scientists detect mysterious warming in US coastal waters

Scientists detect mysterious warming in US coastal waters

Unprecedented ocean temperature rises off the Atlantic and Pacific coasts of the US may be linked to sea level rise or the recent pattern of “weird” weather.

LONDON, 28 June, 2015 − Oceanographers are puzzled by an accelerated burst of warming sea that threatens the fisheries of the American Atlantic coast.

Meanwhile, off the US West coast, scientists report that they have been baffled by a mysterious “blob” of water up to 4°C warmer than the surrounding Pacific, linked to weird weather across the entire country.

Jacob Forsyth and research colleagues from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts report in the Journal of Geophysical Research: Oceans that the ocean off the US north-east continental shelf has been warming at unprecedented levels for 13 years.

Their findings came after analysis of data from sensors − called bathythermographs − dropped 14 times a year from the container ship Oleander, which for 37 years has travelled between New Jersey and Bermuda. Each detector takes the temperature of the water column as it sinks up to 700 metres.

Startling discovery

What they were startled to discover was an unexplained, and unprecedented, rise in the water temperatures that may be linked with an equally mysterious sea level anomaly: sea levels are going up, but they are going up faster off the north-east coast of the US than almost anywhere else.

“The warming rate since 2002 is 15 times faster than from the previous 100 years,” says Glen Gawarkiewicz, a WHOI senior scientist and one of the authors of the report.

“There’s just been this incredible acceleration to the warming, and we don’t know if it’s decadal variability or if this trend will continue.”

“It’s producing conditions that we think are going to be more common with global warming”

To make sure of their perspective, the authors compared their analysis with surface data from the Nantucket lightship and other such installations along the coast, from 1880 to 2004. The new study shows that the warming is not just confined to surface waters.

Although there must be some link with the steady rise in atmospheric temperatures because of global warming as a result of human-made carbon dioxide emissions, the oceanographers suspect there may also be another explanation, so far undiscovered.

Off the Pacific coast, meteorologists have been scratching their heads over the appearance in 2014 of a “remarkably” warm patch −  1,500 kilometres across in every direction and 100 metres deep − that could be linked to “weird” weather across the continental US that has seen heat and drought in the west and blizzards and chills in the East.

High pressure ridge

Nicholas Bond,  a research meteorologist at the University of Washington in Seattle, and colleagues report in Geophysical Research Letters that what they have called “the blob” was linked to a persistent high pressure ridge, linked in turn to a calmer ocean during the last two northern hemisphere winters.

The blob plays a sure role in the West Coast weather. Air sweeping across it picks up heat, and this results in warmer temperatures and lower snowpack in coastal mountains − which certainly stoke up the conditions for drought.

A second study in Geophysical Research Letters links the warm Pacific puzzle to the big freeze in the eastern states in 2013 and 2014.

Once again, there doesn’t seem to be a direct connection with climate change, but it raises the spectre of changes to come.

“This is a taste of what the ocean will be like in future decades,” Dr Bond says. “It wasn’t caused by global warming, but it’s producing conditions that we think are going to be more common with global warming.” − Climate News Network

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Global warming means double jeopardy for sea life

Global warming means double jeopardy for sea life

Some sea creatures seeking to escape warming oceans as the mercury rises will find that climate change is damaging the areas which could give them refuge.

LONDON, 9 June, 2015 − Global warming is likely to drive marine creatures away from the equator in search of new and cooler habitats − and  is likely to limit the safest options for many migrant fish, crabs and corals.

One problem for marine life is that warmer waters hold less oxygen, so the corals that move to higher latitudes will have to settle in shallower water to take advantage of the diminishing light. This, too, creates hazards.

Curtis Deutsch, an oceanographer at the University of Washington in the US, and colleagues report in the journal Science that the ocean’s denizens could be heading for respiratory stress. Warmer waters speed up the metabolic need for oxygen, but those same warmer waters hold lower levels of dissolved gases.

“If your metabolism goes up, you need more food and you need more oxygen,” Dr Deutsch says. “This means that aquatic animals could become oxygen-starved in the warmer future, even if oxygen doesn’t change. We know that oxygen levels in the ocean are going down now, and will decrease more with climate warming.”

Shifting habitats

His co-author, Hans-Otto Pörtner, head of the Department of Integrative Ecophysiology at the Alfred Wegener Institute in Bremerhaven, Germany, says: “If the oxygen level in a given region of the ocean drops below a species’ minimum requirements, it forces the animals to abandon their native habitat. This combines with the effect of warmer temperatures.

“Since animals evade to cooler regions, their habitat shifts towards the poles or to greater water depths. In Atlantic cod and many other fish species, we can already observe the shift now.”

That change is undoubtedly on the way. One group has just calculated that between 50% and 70% of the world’s oceans could see changes in biodiversity as the sea surface temperatures creep upwards.

The next question is: what kinds of change and what kinds of habitat will be available for submarine climate refugees? The researchers chose four well-studied marine species for their simulations of the impact of climate change on the maritime world.

Combined stress

These are the open ocean-dweller Atlantic cod, the coastal water-dwelling Atlantic rock crab, the sharp snout sea bream of the sub-tropical Atlantic and Mediterranean, and the common eelpout, a bottom-dwelling fish that lives in the shallow waters of the high northern latitudes.

The study suggests that, for many species, the combined stress of higher metabolic rates and lower levels of dissolved oxygen will mean that possible habitats will contract by between 14% and 26% because at the present species’ ranges nearer the equator, peak oxygen demand would become greater than the supply.

Also in Science journal, a team led by Paul Muir, acting curator for corals at the Museum of Tropical Queensland in Australia, reports on the potential future for 104 species of staghorn corals – the tiny creatures whose skeletons make up the reefs that offer the richest habitats in the tropical seas.

Corals are sensitive to extremes of temperature. As the mercury levels climb, they can “bleach” and reject the algae on which they depend for survival. And if conditions are too hot for too long, they can perish.

Little sunlight

But the Australian team found that these animals, too, are caught in a kind of habitat trap. As they migrate away from the equator, they must nest in shallower water to take advantage of the lower levels of winter sunlight that penetrate the waters at higher latitudes.

The corals are likely to have to rise 0.6 metres for every one degree of latitude of migration. But there is a limit to how high in the water they can rise because, at a certain point, temperature, salinity and wave damage will start to take their toll.

“The two studies remind us that climate change will reshape marine species’ habitats, but not necessarily expand them,” warns Joan Kleypas, a marine ecologist/geologist at the US National Centre for Atmospheric Research, in the same journal.

“Both studies highlight little-recognised barriers to future range expansions in the oceans,” he says. “Each is based on physiological limitations of marine organisms that are quantifiable, and thus increase our ability to predict species habitats into the future.” − Climate News Network

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Earth has warmed as usual, with no slowdown

Earth has warmed as usual, with no slowdown

US scientists re-examine the collection of data which seemed to show global warming slowing since 1998 and say temperatures have continued to rise steadily.

LONDON, 7 June, 2015 − Forget about the so-called “hiatus” in global warming. The planet’s average temperatures are notching up as swiftly now as they did 20 or 30 years ago.

A team of US researchers has looked again not just at the data for the last 60 years but at how it has been collected, and done the sums again. They conclude, in the journal Science,  that the “estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a ‘slowdown’ in the increase of global surface temperature rise.”

But first, the story-so-far. Climate sceptics have repeatedly claimed that global warming has slowed or stopped. This was not the case: 13 of the hottest years ever recorded have all occurred in the last 14 years, and 2014 was the hottest of them all.

But when climate scientists looked at a graph of the rise of temperatures in the last 60 years, they saw – or thought they saw – a distinct drop in the rate of increase in global average temperatures in the last 15 years.

This apparent dip became the subject of a whole series of studies. Researchers had never expected the rise to follow a straight line – all sorts of natural climate cycles would naturally affect annual records – but the rate of increase was slower, and more sustained in its slowness, than anyone could explain, especially as there had been no drop in the greenhouse gas emissions that drive global warming.

Data anomalies

Some proposed that the expected extra heat in the atmosphere had been drawn down into the great oceans and others that an unnoticed increase in volcanic activity had helped screen the sunlight and cool the atmosphere unexpectedly. Yet another group looked not at average temperature patterns but the change in the frequency of heat waves and saw a different kind of rise.

Yet another group wondered if the problem might be only apparent: more complete data from many more parts of the world might combine to tell a different story. Thomas Karl and colleagues at the National Oceanographic and Atmospheric Administration in the US made this their starting point.

They looked again at how the data had been collected, and the gaps that might have appeared. Sea surface temperatures, for instance, were at different periods collected by bucket from a ship’s deck, by readings aboard surface drifting and moored buoys or by engine-intake thermometers in ships’ engine rooms, and there could be subtle differences not accounted for.

There were very few readings from the Arctic, yet the Arctic is by far the fastest-warming region of the planet, and the pattern of land-based temperature readings, too, repaid re-examination.

By the time the NOAA team had finished, the recalibrated figures told a different story. Between 1998 and 2012, the world warmed at the rate of 0.086°C per decade, more than twice the rate of 0.039°C per decade measured by the Intergovernmental Panel on Climate Change.

“We need to look really carefully at data quality and issues of instrument change”

The new figure is much closer to the rate estimated for the decades 1950 to 1999, at 0.113°C per decade. And the new analysis lifts the rate of warming from 2000 to 2014 to 0.116°C per decade, which if anything is an acceleration, not a slowdown.

British climate scientists have welcomed the finding: it is however the finding of just one group and, like all such research, will be accepted more readily if it can be separately replicated.

“This study makes the important point that we need to look really carefully at data quality and issues of instrument change,” said Piers Forster, professor of climate change at the University of Leeds, UK.

”Yet there are several legitimate judgment calls made when combining datasets to make a global mean-time series. I still don’t think this study will be the last word on this complex subject.”

But Peter Wadhams, a professor of ocean physics at the University of Cambridge, UK, called the study careful and persuasive, and said: “I think it shows clearly that the so-called ‘hiatus’ does not exist and that global warming has continued over the past few years at the same rate as in earlier years.” − Climate News Network

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Climate change could treble risks for marine life

Climate change could treble risks for marine life

Scientists warn that even stabilised levels of fossil fuel use could cause changes to ocean ecosystems far greater than any witnessed in the last 50 years.

LONDON, 4 June, 2015 − Severe global warming – a rise in annual average global temperatures driven by ever-increasing burning of fossil fuels – could force change in up to 70% of the ocean ecosystems, according to new research.

Even moderate global warming, in which greenhouse gas emissions stabilise in the next 25 years, could trigger changes three times greater than any seen in oceans over the last 50 years.

Marine biologist Grégory Beaugrand, of the University of Science and Technology at Lille in France, and colleagues report in Nature Climate Change that they used a new approach to calculate the overall pattern of winners and losers in tomorrow’s world, as carbon dioxide levels in the atmosphere soar and climates change.

They found that tropic and warm water regions would become poorer in living things, with biodiversity decreased. Some species would become extinct, some might adapt, and others would migrate.

Higher latitudes, however, would see a greater mix of living creatures – an increase in diversity of up to 300% – as species migrated north or south towards the polar regions in response to sea temperature change.

Ground-breaking model

The scientists started from the basis that − local variations in fishing, hunting, food supply and water chemistry aside − what mattered in the marine world was mostly temperature.

“We developed a ground-breaking new model for how biodiversity is arranged in the oceans and tested its accuracy using real world examples from plankton to whales − in fact the smallest of sea creatures to the largest,” Dr Beaugrand says.

“The main environmental variable in our model influencing where species like to live is temperature. We demonstrated that our model can reconstruct accurately patterns of marine biodiversity, and then we used it to see how biodiversity may reorganise in response to four different levels of global warming.”

The scientists used the past as a guide to the present and to future change. They compared the distribution of species now with what the fossil record showed for the mid-Pliocene epoch about  three million years ago, when the world was 3°C warmer than it is now, and during the last glacial maximum 20,000 years ago, when the world was 4°C to 5°C cooler.

“Any changes in biodiversity will inevitably affect interactions among species, and consequently how the ecosystem functions”

The researchers from France, Britain and Monaco have once again confirmed that the warmer the planet, the greater the potential change. But most previous research has focused on the impact of climate change on the terrestrial world. In fact, Earth is 70% ocean, and 70% of the planet’s people live within 60km of the shoreline.

Humans survive on the sea’s productivity, landing 80 million tonnes of fish each year, and the oceans play a decisive role in the regulation of the planetary climate.

The oceans have already begun to respond to climate change, as familiar species move north or dive deeper in search of the ideal temperatures in which to thrive, and invasive species eat away at long-established ecosystems.

But it is harder to predict quite how nature rebalances itself in oceans that will also be changed by increasing acidity and pollution.

“Any reorganisation of marine biodiversity will affect us in some way,” Dr Beaugrand says. “Some individual changes may be good, and some may be bad. For example, harmful algal blooms may increase in some places and decrease in others.

Function and productivity

“However, together, any changes in biodiversity will inevitably affect interactions among species, and consequently how the ecosystem functions and how productive it is, which are important aspects to understand and predict.”

If the world’s nations keep to the commitment to limit global warming to below 2°C, only about 15% of the ocean would undergo changes greater than happened over the last 20,000 years, and only 25% would see a change greater than since the mid-Pliocene more than  three million years ago.

However,  at 2°C, between 37% and 46% of the oceans would experience changes in biodiversity, and at higher levels these changes could range from 50% to 70%, the scientists say.

If emissions peak in the next five years and begin to decline, any biological changes might not be very different from existing patterns of variability seen in the last 50 years. But change is on the way.

“Our results show that climate change may rapidly reorganise marine biodiversity over large oceanic regions, and that the intensity of this reorganisation will depend, unsurprisingly, on the magnitude of warming,” the authors conclude. – Climate News Network

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Aerosols may offer short-term lifeline to corals in crisis

Aerosols may offer short-term lifeline to corals in crisis

Reducing the bleaching of corals by blocking the sun’s rays might buy time to keep tropical reefs alive if efforts are increased to halt global warming.

LONDON, 29 May, 2015 − A new solution has been proposed for the forthcoming crisis of the coral reefs: blot out some of the sunlight.

Scientists from the US, UK and Australia suggest a form of climate engineering called solar radiation management, which involves pumping aerosols into the stratosphere to reduce global temperatures − and especially the warming of the tropic seas.

If sea temperatures rise just 1°C to 2°C above the normal summer high, something gruesome happens to the coral reefs: they bleach.

This is because they sicken, and expel the colourful algae with which they cohabit. It is a survival technique known to biologists as symbiosis. But if the bleaching goes on for long enough, they die.

Human-induced warming

Lester Kwiatkowski − a researcher with both the University of Exeter in the UK and the Carnegie Institution for Science in the US − and colleagues report in Nature Climate Change that human-induced global warming because of the burning of fossil fuels could raise temperatures enough by 2050 to bleach and degrade 90% of the world’s coral reefs.

So, the authors argue, the world must accept that the loss of the reefs is inevitable − or buy time to save them.

The latter option could be addressed by squirting massive quantities of sulphate aerosols into the stratosphere to reflect radiation and darken the skies, while humans get on with the much-delayed challenge of reducing atmospheric carbon dioxide concentrations by switching to renewable sources of energy.

The irony is that Dr Kwiatkowski has only lately dismissed at least one ocean geoengineering solution – to cool the sea surfaces by pumping up cold water from the ocean depths – because, in the long run, it might make the climate change crisis even worse. Nor is he the only scientist to make that point.

“We need to accept that the loss of a large percentage of the world’s reefs is inevitable,
or start thinking beyond conventional
mitigation of CO2 emissions”

Geoengineering has repeatedly been defined as the wrong answer to problems of soaring human numbers and uncontrolled economic growth.

So the real message of this latest study may be that the choices facing humankind have become increasingly unwelcome.

Coral reefs are the richest ecosystems in the oceans, and 500 million people depend on the living coral and its co-dependants for food, tourist income and coastal protection.

The tropical reefs have bleached before, in extremes of heat, but after a few years have recovered. Whether they could survive both a sustained rise in temperatures and the increasing acidification of the oceans that goes with higher carbon dioxide levels is another matter.

Ecosystem at risk

So the researchers decided to see what it would take to reduce the risk. They took some account of the impact of the debilitating effect of increasing ocean acidity. Then they considered the hypothetical fate of corals in a warming world.

There is no doubt that bleaching is a consequence of hotter seas, or that by 2100 the entire reef ecosystem will be at risk.

At least one other group has proposed that some form of solar protection could be an answer, but another has suggested that at least some corals might adapt.

“Coral reefs face a dire situation, regardless of how intensively society decarbonises the economy,” says Peter Cox, professor of climate system dynamics at the University of Exeter.

“In reality, there is no direct choice between conventional mitigation and climate engineering, but this study shows that we need to accept that the loss of a large percentage of the world’s reefs is inevitable, or start thinking beyond conventional mitigation of CO2 emissions.” – Climate News Network

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Rising temperatures mean fewer but fiercer hurricanes

Rising temperatures mean fewer but fiercer hurricanes

Climate change brings mixed prospects for people threatened by hurricanes: they are likely to occur less often, but when they do they will be even more destructive.

LONDON, 25 May, 2015 − Once again, scientists have confirmed the link between climate change and destructive hurricanes. The link is a simple one: a warmer world could mean fewer tropical storms, but those that arrive are likely to be more violent.

The conclusion is not new: other teams have already proposed that global warming linked to increases of carbon dioxide in the atmosphere as a consequence of fossil fuel combustion could drive tropical cyclones to higher latitudes and that the most destructive hurricanes could happen increasingly often. A British team has even linked better air quality – fewer sulphate aerosols and dust – to a greater probability of more violent winds.

But Nam-Young Kang, who now directs South Korea’s National Typhoon Center, and James Eisner, a geographer at Florida State University, set about a study of weather data and hurricane, cyclone and typhoon records between 1984 and 2012 to see if they could identify a pattern of change.

In the last 60 years or so, global average temperatures have risen, but are still less than 1°C above the average for the centuries before the Industrial Revolution. Hurricanes are linked to sea surface temperatures and the hurricane “season” does not start until ocean surface levels go beyond 26°C.

“We’re seeing fewer hurricanes, but the ones we do see are more intense. When one comes, all hell breaks loose”

The two scientists reckoned that even slightly higher average temperatures would mean more energy and therefore higher wind speeds at sea as well. They report in Nature Climate Change that they found what they were looking for: a pattern. On average, storm wind speeds had increased by 1.3 metres a second and there were 6.1 fewer tropical storms a year worldwide than there would have been if land and water temperatures had remained constant.

The research paper describes tropical cyclones – a term that for geographers also embraces Pacific typhoons and Atlantic hurricanes – as “perhaps the least welcomed natural phenomena on our planet” and points out that even well-developed, highly complex societies are exposed to them, and vulnerable. Superstorm Sandy, which began as an Atlantic hurricane, hit New York in 2012 with devastating consequences and even set the nation’s earthquake alarms ringing.

Professor Eisner has already established a link between temperatures and tornado hazard.  The new study delivers a statistical warning of a trade-off between frequency and strength offshore as well.“We’re seeing fewer hurricanes, but the ones we do see are more intense. When one comes, all hell breaks loose,” he said. − Climate News Network

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Antarctic ice is under attack from sea and air

Antarctic ice is under attack from sea and air

Satellite and radar studies show that twin forces causing the vast ice shelf to thin and become less stable could have a serious impact on global sea levels.

LONDON, 18 May, 2015 − Scientists have measured the rate of thinning of the great sea ice shelf of the Antarctic Peninsula and have identified the mechanisms at work above and below the shelf.

The collapse of floating sea ice makes no direct difference to global sea levels – but the effects could nevertheless lead to higher waters everywhere.

Paul Holland, of the British Antarctic Survey (BAS), and research colleagues from the US report in the journal The Cryosphere that they used satellite measurements and radar studies between 1998 and 2012 to confirm that the Larsen C ice shelf has lost four metres of ice, and is a metre lower at the surface.

Warmer waters

This is the largest of three shelves that have been under study for decades; the Larsen A and Larsen B shelves have already broken off and drifted north to warmer waters.

The Antarctic Peninsula is one of the fastest-warming regions of the world: 2.5°C in the last 50 years.

“What’s exciting about this study is we now know that two different processes are causing Larsen C to thin and become less stable,” says Dr Paul Holland, lead author of the BAS study.

“Air is being lost from the top layer of snow (called the firn), which is becoming more compacted, probably because of increased melting by a warmer atmosphere.

“We expect that sea-level rise around the world will be something in excess of 50 cm higher by 2100 than it is at present”

“We know also that Larsen C is losing ice, probably from warmer ocean currents or changing ice flow. If this vast ice shelf − which is over two and a half times the size of Wales, and 10 times bigger than Larsen B − was to collapse, it would allow the tributary glaciers behind it to flow faster into the sea. This would then contribute to sea-level rise.”

A collapse of the shelf could occur within a century. When the two companion Larsen glaciers broke away, the glaciers that flowed from the ice-capped continent towards the sea began to accelerate.

Offshore ice, held fast to the shoreline, is a factor that helps keep glacier flow at its proverbially glacial pace. Once it has gone, the frozen rivers of ice onshore naturally begin to flow faster.

“We expect that sea-level rise around the world will be something in excess of 50 cm higher by 2100 than it is at present, and that will cause problems for coastal and low-lying cities,” says David Vaughan, director of science at the BAS.

“Understanding and counting up these small contributions from Larsen C and all the glaciers around the world is very important if we are to project, with confidence, the rate of sea-level rise into the future.”

The study is a confirmation of earlier research in which other groups, using different approaches, have already identified shelf ice loss and have warned that Antarctic melting could accelerate. Satellite-based measurements have also linked glacial melting with an acceleration in sea level rise.

Precision measurement of sea level rise is not easy. Oceans rise and fall with the tides, the water isn’t level anyway, and salinity and temperature differences in the oceans, and gravitational anomalies in the ocean basins, all mean that the ocean surfaces naturally undulate.

And the continents don’t keep still. Land surfaces from which researchers base their measurements also slowly rise or fall.

Accelerated rise

Christopher Watson, senior lecturer in the School of Land and Earth at the University of Tasmania, Australia, and colleagues report in Nature Climate Change that a different approach to the problem suggests that – contrary to previous estimates – sea level rise has accelerated in the last decade.

He and his colleagues searched not just global positioning satellite evidence from the surface waters but also from the land for signs of “bias” in the data. They also used evidence from hourly tide gauges from around the world and recalculated the rate of change.

What they found was that, overall, sea level rise in the last two decades has been at a rate just under, rather than just over, 3mm a year.

But the overestimate for the first six years of the survey had been much higher, which in turn suggested that the rate of rise had actually accelerated during this century, in a way that is consistent with the rate of glacial melting − at least from the Greenland and West Antarctic ice caps. – Climate News Network

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Plant growth may speed up Arctic warming

Plant growth may speed up Arctic warming

Arctic plants may absorb more greenhouse gases as the region warms – but scientists say this could intensify the warming rather than moderate it.

LONDON, 10 May, 2015 – Green may not automatically mean innocent or planet-friendly after all. Korean and German scientists have identified a mechanism that could encourage plants to take up more carbon dioxide – and at the same time amplify Arctic warming by 20%. This counter-intuitive finding is published in the Proceedings of the National Academy of Sciences.

Jong-Yeon Park of the Max Planck Institute for Meteorology and colleagues have been looking at the role of phytoplankton, those tiny marine plants that flourish around land masses, exploit the nutrients that flow from rivers and turn the blue ocean sea-green. Like any grass or shrub or tree, they exploit sunlight and employ photosynthesis to soak up atmospheric carbon dioxide.

So as the Arctic Ocean warms, because of increasing emissions of carbon dioxide from the burning of fossil fuels, the ice melts, the blue sea water absorbs more sunlight, and the green things get a chance to grow and soak up some of that greenhouse gas as organic carbon in plant tissues. This is what engineers call negative feedback.

But it may not work like that. The scientists matched up a model of the climate system with a model of the ecosystem and did all the sums again. And they found that instead of reducing warming, an explosion of phytoplankton growth could actually amplify it.

More warming

If the seas warmed and the ice melted, then the overall albedo – the reflectivity of the Arctic – would be changed. More high energy solar radiation would get into the sea, and the phytoplankton harvest would be greater and go on for longer.

But more phytoplankton would mean more biological activity, which would directly warm the surface layer of the ocean, “triggering additional positive feedbacks in the Arctic, and consequently warming the Arctic further,” the authors warn.

“We believe that, given the inseparable connection of the Arctic and global climate, the positive feedback in Arctic warming triggered by phytoplankton and their biological heating is a crucial factor that must be taken into consideration when projecting future climate changes,” said Jong-Seong Kug, a professor at Pohang University of Science and Technology in Korea.

Science like this is a reminder that the climate system is a subtle and complex machine driven by sunlight, atmosphere, water – and carbon. A British team has warned that rainforests could in fact be emitting much more carbon than climate modellers have accounted for. That’s because they haven’t allowed for all of the dead wood.

“A large proportion of forests worldwide are less of a sink and more of a source”

Marion Pfeifer of Imperial College and colleagues report in Environmental Research Letters  that they surveyed a large area of forest in Malaysian Borneo to make their calculations.

Pristine, untouched forest is rare. Most forests provide an income for someone, and increasingly parts of the great forests are exploited by loggers and planters. In untouched forests, dead wood makes up less than 20% of the biomass. Dr Pfeifer and her colleagues found that in partially-logged forests, the dead wood could account for 64% of the biomass.

Details such as this could send climate modellers back to the drawing board. That is because the great riddle of climate science is: where does all the carbon go? The assumption has been that forests are “sinks” that collect atmospheric carbon. But that depends on the forest.

“I was surprised by how much of the biomass dead wood accounted for in badly-logged forests. That such logged forests are not properly accounted for in carbon calculations is a significant factor. It means that a large proportion of forests worldwide are less of a sink and more of a source, especially immediately following logging, as carbon dioxide is released from dead wood during decomposition,” Dr Pfeifer said.

“Selectively-logged tropical forests now make up about 30% of rainforests worldwide. That means such global calculations are wrong at least 30% of the time.” – Climate News Network

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