Half of climate safety level has gone

Half of climate safety level has gone

Global temperatures have risen by 1°C in the past 150 years, and one scientist says doubling that level could unleash catastrophic sea level rise this century.

LONDON, 2 August, 2015 – The world is now halfway towards the internationally-agreed safety limit of a maximum 2°C rise in global average temperatures, researchers say.

That limit seeks to prevent the global warming caused by the burning of fossil fuels exceeding 2°C above the pre-industrial global temperature. The UN’s Paris climate summit later this year aims to ensure that it is not breached.

It appears that the human race has taken roughly 250 years to stoke global warming by 1°C. On present trends, we look likely to add the next 1°C far more quickly – across much of the world, many climate scientists believe, by the middle of this century.

The research is published in the journal New Scientist, which commissioned it. As so often with climate projections, it needs qualifying and teasing apart.

Some scientists, for example, warn that there’s uncertainty about just what the pre-industrial global temperature was. The New Scientist research is careful to be specific: it says global surface temperature is now passing 1°C of warming relative to the second half of the 19th century.

Farewell, hiatus

And one of the four main trackers of temperature thinks that milestone will be passed only if there is a strong El Niño, the cyclic Pacific weather phenomenon that periodically brings widespread chaos in its wake.

However, the research looks likely finally to lay to rest the argument that global warming is slowing and stuttering to a virtual halt, the so-called hiatus theory. Kevin Trenberth, of the US National Center for Atmospheric Research in Boulder, Colorado, told New Scientist: There’s a good chance the hiatus is over.”

The hottest year since records began was by a very small margin – 2014, and this year’s El Niño could mean a temperature rise of 0.1°C this year, an increase which usually takes about a decade to develop. Dr Trenberth thinks 2015 is likely also to be a record-breaker. 

Between 1984 and 1998 the Earth warmed at 0.26°C a decade, but the Intergovernmental Panel on Climate Change (IPCC)  says the rate then fell back until 2012 to about 0.04°C, for a number of reasons, including a less active Sun, more cooling aerosols from volcanoes and Asian factories, and more heat being absorbed by the oceans. The New Scientist findings suggest that warming may soon revert to the higher rate. 

From a quite different source comes a warning not only that temperatures may soon start a marked rise, but that sea level may also accelerate far faster than most scientists think likely.

It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable”

The prospect it holds out is at odds with most mainstream climate science, and might well be discounted as alarmist and fanciful. But the lead author of the discussion paper in which it appears is the highly respected James Hansen, former director of NASA’s Goddard Institute for Space Studies.

He and his colleagues say the ice melting around Greenland and Antarctica will cause sea level rises much faster than mainstream predictions suggest, by several metres this century. This will add to a process which they say has already begun, accelerating the melting of the undersides of Antarctic glaciers and ice shelves.

Another consequence, they think, will be the shutting down of ocean currents which carry heat from the tropics to the polar regions, leaving the tropics to warm fast and the high latitudes to cool. This temperature difference, they say, will spawn superstorms unlike any seen so far.

All this, Professor Hansen and his colleagues say, could happen with a 2°C temperature rise, with devastating consequences: It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilisation.”

Professor Hansen may of course be wrong, but it would be short-sighted to assume that he is. He has a strong record of ultimately being proved right. 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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Global warming slowdown offers only fleeting relief

Global warming slowdown offers only fleeting relief

Scientists show that long-term temperature rise is the inevitable consequence of increasing greenhouse gas emissions from fossil fuels.

LONDON, 30 April, 2015 − The so-called hiatus in global warming will probably make no difference to the world in the long run, according to Australian scientists.

Using computer models to take the planetary temperature in 2100, they found that one set of models incorporated the slowdown, but others did not. In the end, the difference was barely significant: less than 0.1°C.

The hiatus is a measurable slowdown in the rate of increase in average global temperatures since the turn of the century.

But since, under the notorious business-as-usual scenario, average planetary temperatures in 2100 will be a predicted 5°C higher than at the start of the Industrial Revolution around 200 years ago, the conclusion is that the slowdown is fleeting.

Drastic steps

In the end, and unless the planet’s governments take concerted and drastic steps to reduce greenhouse gas emissions from fossil fuels, the outcome will be the same.

The study, the authors say in the journal Nature Climate Change, shows that the slowdown merely reflects short-term variability.

“Our research shows that while there may be short-term fluctuations in global average temperatures, long-term warming of the planet is an inevitable consequence of increasing greenhouse gas concentrations,” says Matthew England, chief investigator at the Centre of Excellence for Climate System Science at the University of New South Wales. “This much-hyped global warming slowdown is just a distraction from the matter in hand.”

It may be a distraction, but Professor England is one of an increasingly large set of researchers puzzling over the mechanisms that may be at work.

“This much-hyped global warming slowdown is just a distraction from the matter in hand”

There is – and climate scientists have confirmed this repeatedly over the last 100 years – a direct link between the planet’s temperature and the levels of carbon dioxide and other greenhouse gases in the atmosphere. In the last 30 years of the last century, planetary average temperatures rose steadily by the decade.

In the first 15 years of this century, the rise has been much smaller, even though the emissions have been greater.

Thirteen of the 14 hottest years ever recorded have fallen in this century, and 2014 was the hottest of them all, but that hasn’t stopped climate scientists from trying to account for the apparent slowdown − perhaps with an aspect of the climate machinery they have so far overlooked.

One group recently suggested that a natural cycle of cooling  in the Antarctic – a cycle much longer and slower than the sketchy data from the southern continent can confirm – has simply masked a continued rise in global temperatures.

Another has pointed to a relatively recent increase in volcanic eruptions that might have delivered enough sulphur aerosols into the atmosphere to block sunlight and to imperceptibly counter the warming trend.

Temporary storage

Braddock Linsley, research professor at the Lamont-Doherty Earth Observatory at Columbia University, New York, and colleagues proposed that the “missing” heat might be in temporary storage in the deep oceans.

And Professor England and colleagues proposed a link between the Pacific trade winds and a natural pattern of ocean circulation − a slow movement sometimes called the Pacific Decadal Oscillation (PDO) − that might be at work, overturning the ocean waters, cooling the surface and burying the warmth.

Now Dr Linsley and colleagues report in Geophysical Research Letters that the trade winds theory might provide at least part of the explanation.

They have been looking  at sea surface temperatures in the southern Pacific back to 1791, as witnessed by the growth of the coral reefs, and have identified a pattern of cyclic change with a period of perhaps about 25 years.

When the PDO goes into reverse, the so-called warming hiatus could end. If the present cycle began around 1999, then it could end quite soon − as early as 2020.

Dr Linsley told the Climate News Network: “There is already some evidence that the PDO may have started reversing late last year.” – Climate News Network

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Commitment to end flaring is boost for climate talks

Commitment to end flaring is boost for climate talks

New initiative to stop gas being flared off from oil production sites could prevent millions of tonnes of emissions being spewed into the atmosphere.

LONDON, 29 April, 2015 − Companies and governments responsible for 40% of global gas flaring have made a commitment to stop their climate-damaging activities within the next 15 years.

Announcing the “Zero Routine Flaring by 2030” initiative at a meeting in Washington DC, the UN Secretary-General, Ban Ki-moon, said its supporters are demonstrating real action in the run-up to the all-important UN conference on climate change in Paris later this year.

“Reducing gas flaring can make a significant contribution towards mitigating climate change,” he said. “I appeal to all oil-producing countries and companies to join this important initiative.”

The World Bank (WB), which launched a Global Gas Flaring Reduction Partnership in 2002, estimates that each year 140 billion cubic metres of natural gas produced together with oil are burned or flared at thousands of oil fields worldwide − adding 350 million tonnes of carbon dioxide emissions to the atmosphere.

Generate power

If the flared gas was used to generate power, the WB says, it would produce more electricity than is at present consumed throughout the African continent.

Flaring – much of which can even be seen from outer space − takes place when there are no facilities to harness the gas, or when oil producers decide it is uneconomical to process or pipe the gas.

Russia is at present the world’s largest flarer − the other big flaring nations being Nigeria, Iraq, Iran, Algeria and Venezuela.

Those committed to ending flaring by 2030 − at the latest – include nine countries, 10 oil companies and six development institutions.

Among the oil companies are Royal Dutch Shell, ENI of Italy, and the Norwegian Statoil group. The countries that say they will end flaring by 2030 include the Russian Federation, Kazakhstan, Gabon and Angola.

And the state oil companies involved include SOCAR of Azerbaijan, Petroamazonas of Ecuador, and the Kuwait Oil Company.

A number of financial institutions and development organisations have also joined the scheme, including the Islamic Development Bank, the African Development Bank, and the European Bank for Reconstruction and Development.

“Gas flaring is a visual reminder that we are wastefully sending CO2 into the atmosphere”

Although the WB says many other countries and oil companies are considering joining the no-flaring initiative, such commitments have been made before – and not fulfilled.

The issue of flaring is particularly contentious in Nigeria’s Niger Delta, the country’s main oil-producing region. Shell, Chevron and other companies, including the Nigerian National Petroleum Company, have made repeated announcements about putting an end to flaring, but the practice is still widespread.

Toxic chemicals released in the flaring process can cause serious health problems, and can damage crops and the environment in surrounding areas.

Nigeria has not so far joined in the WB initiative, and neither has the US, which flares gas from thousands of shale oil production sites.

Beyond money

Faith Nwadishi, a representative of various Nigerian civil society groups, says that those involved in the no-flaring initiative had to make a real commitment to end what she called the evil of gas flaring.

“The issue of gas flaring goes beyond the amount of money that can be saved or how much money people can get out of the business,” she told the Nigeria-based Business News.

“We really have to think about the fact that people are not sensitive to the plight of the people who live in active gas flare sites.”

The WB says that by endorsing the no-flaring initiative, governments, oil companies and development institutions are acknowledging that routine gas flaring is unsustainable – both from resource management and environmental perspectives.

“Gas flaring is a visual reminder that we are wastefully sending CO2 into the atmosphere,” says Jim Yong Kim, the WB president.

“We can do something about this. Together we can take concrete action to end flaring and to use this valuable resource to light the darkness for those without electricity.” – Climate News Network

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Two oceans may explain global warming pause

Two oceans may explain global warming pause

Temperatures may be rising more slowly than expected because of two natural oceanic cycles − the latest refutation of the global warming “pause”.

LONDON, 1 March, 2015 − US scientists have suggested yet another explanation for the so-called pause in global warming. They think it might all be down to the juxtaposition of two independent natural climate cycles – each with periods of half a century or more – one of which is blowing cold, and the other not very hot.

Between them, the phenomena known to meteorologists as the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation could account for the seeming slowdown in predicted temperature rises.

Any pause or hiatus in global warming is only apparent: in fact, 14 of the warmest years on record have happened in the last 15 years and 2014 was scored separately, by the World Meteorological Organisation, the US National Oceanic and Atmospheric Administration, and the US space agency Nasa,  as the warmest on record.

But overall, the palpable increases in average temperatures per decade recorded in the last 30 years of the 20th century have not been maintained, and climate scientists and meteorologists have been trying to work out why.

The latest proposal is from Byron Steinman, a geologist at the University of Minnesota Duluth, and Michael Mann and Sonya Miller of Pennsylvania State University.

Multiple theories

Professor Mann is the scientist who, much to the fury of people who deny climate change, first formulated the famous “hockey-stick graph” which highlights the magnitude of change that threatens to overtake global climate as greenhouse gas levels rise because of human activity.

They report in Science that the northern hemisphere is warming more slowly, not because of the Atlantic oscillation, which has been relatively flat, but because of a second, different but still natural downward trend in the Pacific cycle.

This is not the only explanation on the table. In the past two years Climate News Network has reported that climate scientists certainly expected a slowdown, but just not right now; or that planetary measurements might be incomplete or misleading; or that even though average levels were down, this masked a series of hotter extremes.

The oceans have certainly been under suspicion. One group has already identified the cooling Pacific as a damper on global warming. Another has suggested that in fact the “missing heat” is collecting in the Atlantic depths.

Yet another has questioned the role of the trade winds, while still another has pointed to an upswing in volcanic activity that could have delivered a fine smear of sunblock aerosols to the atmosphere.

“The North Atlantic and North Pacific Oceans appear to be drivers of substantial natural… climate variability on timescales of decades”

Any or all of these could have some role in the big picture. The climate would vary anyway, and the question in every case is: how much would any or all natural variation affect the overall path of change because of increasing carbon dioxide levels in the atmosphere?

The latest study is based on sophisticated climate models that match the predicted impact of the great ocean-atmosphere cycles with the pattern of climate shifts recorded in the past.

“We know that it is important to distinguish between human-caused and natural climate variability so we can assess the impact of human-caused climate change, including drought and weather extremes,” Professor Mann said.

“The North Atlantic and North Pacific Oceans appear to be drivers of substantial natural, internal climate variability on timescales of decades.” – Climate News Network

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Small volcanic eruptions are key to warming hiatus

Small volcanic eruptions are key to warming hiatus

Sulphur dioxide hurled in vast amounts from volcanoes is known to cool the atmosphere, but now scientists have identified how even small eruptions have a big effect on climate.

LONDON, 13 January, 2015 − Researchers now have a new explanation for the so-called slowdown in global warming in this century. They blame it on not very dramatic, small-scale volcanic eruptions.

This is a new twist in a puzzling story. In 1991, a catastrophic eruption of Mount Pinatubo in the Philippines hurled 20 million tonnes of sulphur dioxide into the stratosphere − a delivery of aerosols huge enough to block incoming sunlight and actually cool the planet for a couple of years. The assumption since then has been that big volcanic eruptions have enough heft to influence climate.

But in two recent papers, researchers have proposed another hypothesis, and then identified the evidence that a greater number of quite modest eruptions could have the same effect.

Mechanisms at work

To demonstrate such a thing, scientists need to pinpoint the mechanisms at work. In November, David Ridley, an atmospheric scientist at the Massachusetts Institute of Technology, and colleagues focused on the intersection of two atmospheric layers – the atmosphere and troposphere.

They used a mix of ground, air and space-based technology to observe the aerosols in the lower stratosphere, and then they played with a climate model. The conclusions were straightforward: volcanoes could have caused a cooling of between 0.05°C and 0.12°C since 2000.

And the latest study, by a team led by Benjamin Santer, an atmospheric scientist at the Lawrence Livermore National Laboratory in California, has shown that the “signals” of eruptions in the late 20th and early 21st centuries can be positively identified in the atmospheric temperature, moisture and reflected radiation at the top of the atmosphere.

This signal, they report in Geophysical Research Letters, doesn’t explain all the hiatus or slowdown. But it makes a significant contribution.

Uptick in activity

Very roughly, there are 1,500 active volcanoes on the planet and, during 1990, there were 53 recorded eruptions. In 2010, there were 83; in 2013, there were a record 84. So it looks as if an uptick in geothermal activity could have made a difference.

But the climate machine is not a simple thing, and the argument is likely to go on. Other researchers have proposed that the missing heat is concealed in the ocean depths, or that a change in the trade winds may be a factor, or that climate scientists may have misread the signals because the extremes in the last 15 years have been hotter, even if the average has not increased much.

So, all along, the discussion has been not just about what might have been missed, but also about precisely what should or could be measured. And, in any case, words such as “pause”, “hiatus” and even “slowdown” add to the confusion.

Early in December, meteorologists declared 2014 on course to be the warmest year ever. It may not prove so – the calculations will take a few more weeks – but even if it isn’t, 14 of the 15 warmest years ever recorded have all occurred in the 21st century. – Climate News Network

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Atlantic depths may hold key to heat hiatus

Atlantic depths may hold key to heat hiatus

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

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Climate change heralds end of civilisations

Climate change heralds end of civilisations

New research supports the growing body of evidence that many past civilisations have collapsed because of climate change. So is history repeating itself?

LONDON, 13 August, 2014 –  Scientists looking at what is known as the “Fertile Crescent” of ancient Mesopotamia have found new evidence that drought caused by climate change brings an end to civilisations.

It is the latest study that confirms the threat posed to present civilisations in Africa, Asia and parts of the United States by changes in rainfall pattern that could lead to the abandonment of once-fertile areas − and the cities that once were fed by them.

The focus of research by a team from Tübingen University, Germany, is the area currently part of Iraq and the Persian Gulf where the development of ancient agriculture led to the rise of large cities.

Evidence from grain samples up to 12,000 years old shows that while the weather was good, the soil fertile and the irrigation system well managed, civilisation grew and prospered. When the climate changed and rainfall became intermittent, agriculture collapsed and the cities were abandoned.

Analysed grains

Dr Simone Riehl, of the Institute for Archaeological Sciences and the Senckenberg Center for Human Evolution and Palaeoenvironment at Tübingen University, analysed grains of barley up to 12,000 years old from 33 locations across the Fertile Crescent to find out if they had had enough water while growing and ripening.

The 1,037 ancient samples were between 12,000 and 2,500 years old. They were compared with modern samples from 13 locations in the former Fertile Crescent.

Dr. Riehl and her team measured the grains’ content of two stable carbon isotopes.

When barley grass gets insufficient water while growing, the proportion of heavier carbon isotopes deposited in its cells will be higher than normal. The two isotopes 12C and 13C remain stable for thousands of years and can be measured precisely – giving Riehl and her colleagues reliable information on the availability of water while the plants were growing.

They found that many settlements were affected by drought linked to major climate fluctuations. “Geographic factors and technologies introduced by humans played a big role and influenced societies’ options for development, as well as their particular ways of dealing with drought,” Riehl says.

Her findings indicate that harvests in coastal regions of the northern Levant, at the eastern end of the Mediterranean Sea, were little affected by drought. But further inland, drought led to the need for irrigation or, in extreme cases, abandonment of the settlement.

The findings give archaeologists clues as to how early agricultural societies dealt with climate fluctuations and differing local environments. “They can also help evaluate current conditions in regions with a high risk of crop failures,” Riehl adds.

The study is part of a project, backed by the German Research Foundation, looking into the conditions under which Ancient Near Eastern societies rose and fell.

Scientists carrying out similar research in the Indus Valley, in present Pakistan and north-west India, home to the Harappan Civilisation, also believe that drought was the cause of the civilisation’s demise.

It was characterised by large, well-planned cities with advanced municipal sanitation systems and a script that has never been deciphered. But the Harappans seemed to slowly lose their urban cohesion, and their cities were gradually abandoned.

Cities abandoned

According to an article in Nature in March, a 200-year drought, caused by the failure of the monsoon, led to the abandonment of the cities and the end of the civilisation.

Across the Atlantic, another puzzle was the loss of the Mayan cities and culture in Central America. This was a people that had the time, money and manpower to build massive temples and cities for a population estimated at 13 million.

Many theories have been put forward as to why, over a period of about 200 years from 750 to 950AD, the Mayans abandoned their way of life. Research on the subject by Sigma Xi, The Scientific Research Society, says that a series of droughts caused by local climate change was the cause.

With the latest report of the Intergovernmental Panel on Climate Change predicting a faltering of the monsoon that is vital for the Indian sub-continent’s ability to feed itself, it seems as though history could repeat itself. Certainly, some people in India believe it could happen unless action to curb climate change is taken.

Environmental refugees in Africa are also seen as victims of changing weather patterns, and California is suffering a three-year drought that is badly affecting water supplies in this most prosperous of American states. – Climate News Network

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Data adds to confusion over polar sea ice

Data adds to confusion over polar sea ice

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

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How nature affects the carbon cycle

How nature affects the carbon cycle

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In Australia and the Arctic, scientists say, they have found unexpected ways in which natural processes are helping to compensate for global warming.

LONDON, 1 June – The great drylands of the planet – and they cover almost half of the terrestrial surface – may be bigger players in the carbon cycle than anyone had suspected. The world’s semi-arid regions may absorb huge volumes of carbon dioxide from the atmosphere whenever it rains enough.

Benjamin Poulter of Montana State University and colleagues report in Nature that they used a mix of computer-driven accounting methods to work out where the carbon goes after fossil fuel burning emits extra carbon dioxide into the atmosphere. Decades of meticulous measurement confirm that, overall, carbon dioxide levels are increasing inexorably, and the world is warming accordingly.

But inside this big picture is a lot of seasonal and inter-annual variation. So climate scientists, when they try to work out what all this means for future climates, need to understand the carbon cycle better.

The assumption has always been that the most important terrestrial consumers of carbon dioxide were the tropical rainforests. But the match of terrestrial biogeochemical and atmospheric carbon dioxide and global carbon budget accounting models by 13 scientists from the US, Europe and Australia has revealed a different story.

In 2011 more than half of the terrestrial world’s carbon uptake was in the southern hemisphere – which is unexpected because most of the planet’s land surface is in the northern hemisphere – and 60% of this was in Australia.

Natural brake

That is, after a procession of unusually rainy years, and catastrophic flooding, the vegetation burst forth and the normally empty arid centre of Australia bloomed. Vegetation cover expanded by 6%.

Human activity now puts 10 billion tonnes of carbon into the atmosphere annually, and vegetation in 2011 mopped up 4.1 billion tonnes of that, mostly in Australia.

There remains a great deal of uncertainty about the carbon cycle and how the soils and the trees manage the extra carbon. Nobody knows what will happen to this extra carbon now in the hot dry landscapes of Australia: will it be tucked away in the soil? Will it be returned to the atmosphere by subsequent bushfires? As scientists are fond of saying, more research is necessary.

But this is an example of negative feedback: as carbon dioxide levels and temperatures rise, the green things respond, and slow the acceleration of both. This is quite different from the positive feedback that follows when Arctic ice – which reflects sunlight – melts and gives way to blue water which absorbs solar energy, thus accelerating the melting.

But even the slow disaster of the polar regions could be accompanied by an ameliorating process. British researchers report in Nature Communications that the ice sheet meltwaters may be rich in iron. A boost of iron would stimulate phytoplankton growth, which means more carbon dioxide could accordingly be absorbed from the atmosphere.

Feeding the oceans

The scientists collected meltwater from a Greenland glacier in the summer of 2012, and then tested it to discover significant quantities of what geochemists call “bio-available” iron.

So, in another example of those cycles of the elements that make the world go round, ice that scrapes over rock also delivers vital nutrients to the sea, for marine plants to take up yet more carbon dioxide and flourish more vigorously in the oceans and keep the planet a little cooler.

The Greenland research gives scientists a chance to estimate more accurately the delivery of this dietary supplement to the oceans: they reckon somewhere between 400,000 and 2.5 million tonnes a year in Greenland and somewhere between 60,000 and 100,000 tonnes in Antarctica. Or, to put it more graphically, it would be like dropping 3,000 fully-laden Boeing 747s into the ocean each year.

“The Greenland and Antarctic ice sheets cover around 10% of the global land surface,” said Jon Hawkings, of the University of Bristol, UK. “Our finding that there is also significant iron discharged in runoff from large ice sheet catchments is new. This means that relatively high concentrations are released from the ice sheet all summer, providing a continuous source of iron to the coastal ocean.” – Climate News Network

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