Fall of ancient civilization offers climate warning

Fall of ancient civilization offers climate warning

Prolonged drought – a familiar climate-related issue in the modern world – is believed by scholars to have been a key factor in the implosion of the powerful Assyrian empire 2,700 years ago.

LONDON, 19 November, 2014 − Two scholars have a new explanation for the collapse of one of the great Bronze Age civilizations. The Assyrian empire of the 7th century BC – based in Nineveh, in what is now northern Iraq – may have collapsed at least in part because of a population explosion and climate change in the form of sustained drought.

And, they point out, there are lessons in ancient history for the modern world as well.

Adam Schneider, an anthropologist at the University of California, San Diego, and Selim Adali, of the Research Centre for Anatolian Civilizations at Koç University in Istanbul, Turkey, put forward their proposal in the journal Climatic Change.

They say that demographic and climatic factors played an indirect but significant role in the collapse of a civilization chronicled not just in clay tablets and archaeological marvels but in the Hebrew scriptures and the Christian Old Testament.

Historic links

The climate change theory of history is now well established. In the last two years, researchers have linked both the dissolution of the Minoan empire in the ancient Mediterranean and the collapse of Levantine civilizations of the near East and the Harappan civilization of the Indus Valley to sustained drought.

Others have identified seasons of plentiful rainfall as the impetus for the conquest of Russia, China and Persia by the Mongol horsemen of Genghis Khan.

The connections with modern conflict, too, have been made before. In 21 studies of upheaval and conflict in modern societies, researchers have found clear links with rises in temperatures.

And just days after the Assyrian study was published in Climatic Change, research in the Proceedings of the National Academy of Sciences identified a link between temperature and rainfall anomalies in sub-Saharan Africa and violence in the region during the last 30 years.

“Hindsight . . . allows us to piece together from the past what can go wrong if we choose not to enact policies that promote longer-term sustainability”

Schneider and Adali looked through what climate scientists call “proxy evidence” of rainfall patterns in the Tigris Valley of northern Iraq more than two and a half millennia ago.

They considered the evidence of lake sediments and confirmed that many parts of the region experienced a “short but widespread dry phase” during the mid-to-late 7th century BC.

They also unearthed written evidence from 666 BC that welcomed “copious rains, huge floods, a fine rate of exchange…” to mark a new accession to the throne. But by 657 BC, another letter stated that “this year’s rains were diminished and no harvest was reaped”.

In fact, Assyrian engineers had established an impressive series of canals, waterways, cisterns and reservoirs to conserve water, and archaeological finds reveal that the imperial farmers grew barley and wheat, grapes, cucumbers, pomegranates, flax and cotton among many other crops.

But demand, too, was on the increase. The empire of built by Sennacherib, a king identified in biblical chronicles, had ambitions for the local populations. In at least 20 known acts of mass deportation, half a million people were resettled in the heartland.

Nineveh grew fivefold in area, and the population growth, the scientists think, placed significant strains on the immediate supplies of food in the region.

Conflict and insurrection

Within five years of the 657 BC drought, the Assyrian economy was struggling, and conflict and insurrection had broken out. By 609 BC, a remarkable civilization had been destroyed.

A multi-year drought, the researchers argue, “would have placed serious stress on the agricultural economy of the Assyrian state and, by extension, upon the imperial political system”.

They see parallels with today, as the fate of the Assyrian empire offers lessons for modern society about the hazards of valuing short-term economic growth over long-term security and sustainability.

“The Assyrians can be ‘excused’ to some extent,” they conclude, “for focusing on short-term economic or political goals that increased their risk of being negatively impacted by climate change, given their technological capacity and their level of scientific understanding about how the natural world works.

“We, however, have no such excuses, and we also possess the additional benefit of hindsight, which allows us to piece together from the past what can go wrong if we choose not to enact policies that promote longer-term sustainability.” – Climate News Network

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Climate threatens striking change to US weather

Climate threatens striking change to US weather

Global warming is expected to have an explosive effect across America as scientists predict that there could be a 50% increase this century in the frequency of lightning strikes.

LONDON, 17 November, 2014 − Climate scientists foresee a brighter future for America − but no one will thank them for it, as global warming is expected to increase the total number of lightning strikes across the US this century by 50%.

David Romps, assistant professor in the Department of Earth and Planetary Science at the University of California, Berkeley, and colleagues report in Science journal that they looked at predictions of rainfall, snow, hail and cloud buoyancy in 11 different climate models. They concluded that the outcome could only be more atmospheric electrical action.

Right now, the continental US is hit about 25 million times a year by lightning.

But Dr Romps said: “With warming, thunderstorms become more explosive. This has to do with water vapour, which is the fuel for explosive deep convection in the atmosphere. Warming causes there to be more water vapour in the atmosphere, and if you have more fuel lying around, when you get ignition, it can go big time.”

More evaporation

Warmer weather means more evaporation. But higher temperatures also mean that the atmosphere’s capacity to hold water vapour increases as well, with a potential for more clouds, more flow of air, and more precipitation.

The volume of water hitting the ground – as hail, snow, sleet or rain – offers a measure of the convection properties of the atmosphere, and convection generates lightning.

Hundreds of people are struck by lightning each year, and scores are killed, but these remain a very small proportion of accidental deaths in any year. The real hazard might lie far from populated areas: half of all wildfires are caused by lightning strikes.

Lightning also generates more nitrous oxides in the atmosphere, which could also affect atmospheric chemistry. So it makes sense to know what to expect as the planet warms.

“We already know that . . . the more precipitation,
the more lightning”

The scientists examined US Weather Service data for 2011, and the counts from the National Lightning Detection Network, to see if they could confirm a link between cloud buoyancy and precipitation as a predictor of lightning. They also looked at data from balloon-borne instruments released every day in the US to measure the rate at which clouds rise.

As a result, they calculate that 77% of the variation in lightning strikes could be predicted from knowledge of the two conditions.

“Lightning is caused by charge separation within clouds, and to maximise charge separation you have to loft more water vapour and heavy ice particles into the atmosphere,” Dr Romps said. “We already know that the faster the updrafts, the more lightning, and the more precipitation, the more lightning.”

Potential energy

Their climate models predicted, on average, an 11% increase in convective available potential energy for every extra degree Celsius rise in average temperatures. They calculated that if average planetary temperatures were to rise by 4°C, the potential for lightning strikes would go up by 50%.

Their calculations are limited to the US mainland and may not apply equally to other parts of the planet. Overall conditions, and therefore the potential for thunderstorms, tend to vary widely.

But the continental US – the predictions do not include Hawaii or Alaska − is flanked by two oceans and with a subtropical sea to its south. It is distinguished by a sharp temperature gradient and dramatic topography, and is already a forge for fierce and destructive tornadoes, and a target for frequent hurricanes.

So the barometer remains set for future storms, with added lightning. – Climate News Network

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Salt’s poisonous effect is growing threat to crops

Salt’s poisonous effect is growing threat to crops

As global warming increases the world’s arid areas, scientists warn that restoring productivity to salt-affected agricultural land will be essential to feed an expanding population.

LONDON, 1 November, 2014 − Salt is poisoning around 2,000 hectares of irrigated farm land every day – and has been doing so for the last 20 years, according to new research.

Think of an area about the size of 3,000 football fields that can no longer be used to produce food each day. And then remember that the global population actually grows by around 200,000 people every day.

Manzoor Qadir, senior research fellow at the United Nations University’s Institute for Water, Environment and Health, and colleagues report in the journal Natural Resources Forum that an area of farmland the size of France – 62 million hectares – has been affected by the build-up of salts in irrigated soil. This is one-fifth of all irrigated land.

“To feed the world’s anticipated nine billion people by 2050, and with little new productive land available, it’s a case of all lands needed on deck,” says Dr Qadir. “We can’t afford not to restore the productivity of salt-affected lands.”

Ancient hazard

Salts degradation is an ancient hazard in arid and semi-arid lands, where groundwater is pumped from aquifers below the bedrock and used to grow crops.

Evaporation and transpiration leave precipitated salts around the roots of each crop and – since there is no fresh rainwater to wash away the salts − sooner or later the levels build up to intolerable scales, and the land becomes increasingly unproductive.

The UN Food and Agriculture Organisation warns that to feed the projected 2050 population, farmers will need to grow 70% more food. Cereal production alone will have to increase by 50%, to a total of three billion tonnes a year. But, each week, the world loses an area of land the size of Manhattan to salt degradation, thanks to poor soil management, bad drainage and other problems.

The researchers, from Canada, Jordan, Pakistan and Sri Lanka, based their estimates on more than 20 studies in the last two decades in Australia, India, Pakistan, Spain, Central Asia and the US.

They also totted up the estimated economic losses: more than $27 billion a year.

In the Indo-Gangetic basin of India, the build-up of soil salts could reduce wheat harvests by 40%, and cotton by more than 60%.

Employment losses could be as much as 50-80 man days per hectare, and human health problems could be between 20% and 40% greater because of the effect. Animal health problems could increase by anywhere between 15% and 50%.

In the Indus basin in Pakistan, the average overall wheat grain loss has been put at 32%, and the average rice yield has fallen by 48%.

The worst affected regions of the world are the Aral Sea basin in Central Asia, the Indo-Gangetic basin in India, the Indus Basin in Pakistan, the Yellow River basin in China, the Euphrates basin in Syria and Iraq, the Murray-Darling in Australia, and the San Joaquin Valley in the US.

The researchers warn that their calculations concern only crop-yield losses.

“Salt-affected degraded lands emit more greenhouse gases, thus contributing to global warming”

“However, the crop yields from irrigated areas not affected by salinisation have increased since 1990 due to factors such as improved crop varieties, efficient on-farm practices, better fertilizer use, and efficient water management practices,” they say.

“Consequently, there may be larger gaps in crop yields harvested from salt-affected and non-affected areas under similar agro-ecosystems, suggesting an underestimation of the economic cost of salt-induced land degradation.”

“These costs are expected to be even higher when other cost components − such as infrastructure deterioration (including roads, railways, and buildings), losses in property values of farms with degraded land, and the social cost of farm businesses − are taken into consideration.

“In addition, there could be additional environmental costs associated with salt-affected degraded lands as these lands emit more greenhouse gases, thus contributing to global warming.”

Some yield could be recovered. For example, farmers could irrigate more sparingly, plough deeply, dig drains, plant trees, select salt-tolerant crops, and dig in the stubble and plant waste.

An essay in the journal Trends in Plant Sciences also notes that around three hectares of farmland are lost every minute.

But plant science itself could help. Sergey Shabala, professor of crop physiology and plant nutrition at the University of Tasmania in Australia,  points out that millions of years of evolution have already devised a possible answer.

He says: “We should learn from nature and do what halophytes, or naturally salt-loving plants, are doing: taking up salt but depositing it in a safe place – external balloon-like structures called salt-bladders.”

Over-riding problem

New approaches to plant breeding could certainly provide part of the solution. The over-riding problem, however, is that water is already being used on a prodigal scale, in a globally-warming world in which some regions are in any case predicted to become even more arid.

Nine-tenths of the Aral Sea – once the world’s fourth largest lake − in Central Asia is now a sandy desert. The dust blown from it has salted half of Uzbekistan’s soil, and 70% of Turkmenistan has become desert, according to a report in the journal Nature.

But the cotton and wheat farmers in the republics that border the Aral Sea are among the highest users of water in the world. A Turkmen, on average, consumes four times the water used by a US citizen, and 13 times that of a Chinese one.

And although the Western hemisphere is in the grip of a calamitous and sustained drought, the real problem, according to Marcia McNutt, the former director of the US Geological Survey, and now the editor-in-chief of Science magazine, is that underground aquifers in the south-western US have been emptied for irrigation at such a rate that the contours on the land itself have started to change.

Californian mountains have risen up to 15 millimetres because of the water loss.

“It is high time we started managing our precious water supplies in harmony with the laws of nature,” she warns. – Climate News Network

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Towering ambition to help protect Amazon rainforest

Towering ambition to help protect Amazon rainforest

A new 325-metre observatory soaring above the Amazonian tree canopy will capture vital data on how climate change is impacting on a delicate environment that is also under threat from encroachment by lawless urban settlements.

SÃO PAULO, 24 October, 2014 − In the Amazon, everything is big – the trees, the rivers, the snakes, and the statistics that measure everything in numbers of football fields or areas the size of entire countries.

Now one of the biggest towers in the world – taller than the Eiffel Tower in Paris and the Chrysler Building in Chicago − is about to rise above the rainforest.

The purpose of the 325-metre (1,066 feet) Amazon Tall Tower Observatory (ATTO) is to gather vital information on how climate change is affecting the Amazon ecosystem and other humid tropical areas, using climate models.

The research project is being run by Brazil’s National Institute for Amazonia Research (INPA), and the Max Planck Institute for Chemistry, Germany. As one of the project directors, Paulo Ataxo, of the University of São Paulo, explains: “The tower will help us answer innumerable questions related to global climate change.”

Jointly financed by the Brazilian and German governments, the ATTO – which has taken seven years to plan and build − is located 100 miles from the city of Manaus. The steel girders had to be transported 4,000 km by road and river from the factory in southern Brazil, and finally up a dirt track into the heart of the forest.

Monitoring network

The ATTO, adding to a network of smaller observation towers already in the area, will be able to monitor − without direct human influence − changes in air masses over an area of hundreds of miles.. It is expected to be in operation for at least 20 years, measuring the wind, humidity, carbon absorption, cloud formation and meteorological patterns in the soil, tree tops, and the air above, adding to the growing body of research showing how vital it is to stop deforestation.

Philip Fearnside, INPA research professor who has been studying the rainforest for over 40 years, says that the loss of natural tree cover is influencing the delicate environmental equilibrium of the region, and of the rest of the country. He says: “Among other services, the forest recycles water, which is critical for the rains in São Paulo , stores carbon, avoiding the worsening of global warming, and maintains biodiversity.”

A recent study by Brazilian, Canadian and German scientists from São Paulo Universities UNESP and USP, Toronto University, and the Hemholtz Centre for Environmental Research in Germany concluded that the deforestation of tropical forests emits at least 20% more CO2 than previously thought.

“Among other services, the forest recycles water,
which is critical for the rains in São Paulo”

The study, published in the Nature Communications magazine, used remote sensoring, the ecology of the countryside, and modelling of the forest dynamic to develop a new approach that included the previously uncalculated loss of biomass on the edges of forest fragments.

The Brazilian government claims it is reducing deforestation. But, according to Environment Ministry figures, the vast area known as Amazônia Legal, which covers the whole of the Amazon basin, has already lost almost a fifth (18.2%) of its total area of 5 million sq km  − that is, around 900,000 sq km.

Another recent study −  a three-year Amazalert research project begun in 2011 by 14 European and South American institutes, including the Universities of Leeds and Edinburgh and the UK Met Office − has concluded that if present policies continue, the future will be chaotic

Amazalert project looked at the impacts of deforestation and climate change on the Amazon up to 2050.

Human impacts

While there is a constant stream of research on the climate and vegetation of the rainforest, to which ATTO will be contributing, there is much less research and information about the role of human beings and society in the Amazon.

Amazalert found that violence and unplanned growth in the towns on the edges of the Amazon region are also threatening its integrity.

Among Brazil’s 50 towns and cities with the highest murder rates per 100,000 inhabitants, 12 are located in the so-called Arc of Deforestation, which runs around the southern and eastern borders of the rainforest. The report says that violence in these towns has reached the “level of civil war”.

For Amazalert collaborator Andrea Coelho, researcher at the Institute for the Economic, Social and Environmental Development of Pará state (IDESP), the problem is that large-scale mining projects, the paving of roads, and the construction of hydroelectric dams attract lots of people, for whom there is no infrastructure.

When the projects are finished, the workers stay on and become goldminers, extractivists, or land-grabbers. Many are living in miserable conditions, and so criminality erupts.

The huge Belo Monte dam, being built on the Xingu river, is an example. In 2007, there were four cases of drug trafficking in surrounding areas. Last year, there were 238. – Climate News Network

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Climate renews famine risk to Africa’s Sahel

Climate renews famine risk to Africa’s Sahel

With population increasing and food demand far outstripping supply, the Sahel is vulnerable to a new humanitarian crisis − and researchers warn that rising temperatures will only make matters worse.

LONDON, 20 October, 2014 − The Sahel, the arid belt of land that stretches from the Atlantic to the Red Sea and separates the Sahara desert from the African savanna, is no stranger to drought and famine.

Now scientists in Sweden say the Sahel faces another humanitarian crisis even than in the recent past − with the changing climate partly responsible.

Writing in the journal Environmental Research Letters, the researchers from Lund University say people in the Sahel need more food, animal feed and fuel every year. But demand, which has more than doubled over a recent 10-year period, is growing much faster than supply.

Fewer resources

Data from 22 countries shows the result: fewer resources per capita and a continued risk of famine in areas with low primary production – that is, the availability of carbon in the form of plant material for consumption as food, fuel and feed.

Human numbers are part of the reason. Between 2000 and 2010, the population of the Sahel grew from 367 million to 471 million people − an annual rise of 2.2% over the decade.

But crop production remained essentially unchanged, so the margin between supply and demand for primary production is shrinking every year, while the Sahel’s population is forecast to total nearly a billion people by 2050.

Children's graves at a refugee camp in Kenya during the famine in 2011 Image: Andy Hll/Oxfam via Wikimedia Commons
Children’s graves at a Kenyan refugee camp during the 2011 famine
Image: Andy Hall/Oxfam via Wikimedia Commons

Some studies suggest that modern plant strains can withstand the effects of drought better than traditional cultivars, although this was not a focus of the Lund team.

They were mainly concerned with the staple crops grown regionally − such as sorghum and millet, which are used as food for people, with the residues used as fodder for livestock − and with the dry woodlands that provide fuel.

They used remote analysis and satellite images to calculate annual crop production in the 22 countries they studied, and compared the figures with data on population growth and consumption of food, animal feed and fuel. This relationship helps to measure a region’s vulnerability.

The study shows that 19% of the Sahel’s total primary production in 2000 was consumed. Ten years later, consumption had increased to 41%.

Reduced harvest

It says several forecasts suggest that harvests will be reduced as a result of the higher air temperatures the region is now experiencing, even though climate change is predicted to result in the Sahel receiving more rain in future.

So, the researchers say, climate change can only increase the vulnerability of the Sahel.

Asked by the Climate News Network whether higher air temperatures alone were likely to cancel the gains from increased rainfall, one of the study’s authors, Hakim Abdi, a doctoral student in physical geography and ecosystem science at Lund, said: “The short answer is yes. Studies indicate that higher temperatures offset both increased rainfall and CO2 fertilisation.

“Additionally, a recent study found that increase in future rainfall in the Sahel, a region where the soil generally receives little nutrient input and is over-exploited, causes nutrient leaching, and hence induces nitrogen stress.

“When we were in our study site in North Kordofan in Sudan, the most common complaint we received from the villages we visited was the lack of water.

“I think that if a drought occurs with an impact that matches or exceeds the ones in 1972/73 or 1982/83, we will see serious consequences − worse impacts than past ones.” − Climate News Network

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Australia gets early blast of more extreme heat

Australia gets early blast of more extreme heat

Summer has come early across much of Australia – and as temperatures soar to record seasonal levels in many areas, the bushfire season has started well ahead of schedule.

LONDON, 14 October, 2014 − It’s the time of year when many Australians start to think about eating outdoors or heading for the beach after work. Early spring, and the temperatures are rising – particularly this year.

The Australian Government’s Bureau of Meteorology (BOM) says maximum temperatures in September across much of the country were higher than average, with central and south-western areas experiencing their warmest September on record.

Australia is considered to be particularly vulnerable to the effects of a climate change, and 2013 was the country’s hottest year since records began, with average temperatures 1.2˚C above the long-term average.

In one seven-day period in early January last year, record national average temperatures exceeded 39˚C.

Unprecedented levels

September started off cool in Sydney, Australia’s most populated city, but then heated up to unprecedented levels for this time of year. For the first time, temperatures climbed to more than 32˚C for two consecutive days in the month.

Meanwhile, overall September rainfall was 27% below the monthly average − and the dry conditions mean the bushfire season has come early. The south of the island of Tasmania has fared particularly badly, with fires fuelled by dry conditions and high winds.

Areas round Sydney and throughout New South Wales – the country’s most populous state − have also been hit by bushfires, with fire warnings going out to more than a million homeowners.

Despite growing evidence that human-induced climate change is a major reason for Australia heating up, the Liberal-National coalition government led by Prime Minister Tony Abbott has taken little action on the issue.

It has abolished a carbon tax introduced by the previous Labour government, abolished a Climate Commission that gave advice on the impact of warming, and is seeking to downgrade modest renewable energy targets.

Polluting fuel

Australia is one of the world’s leading producers of coal – the most polluting fuel, which is responsible for a significant portion of climate changing greenhouse gas emissions (GHGs). The country’s per capita GHG emissions are among the highest in the world.

A recent report on Australia’s climate, produced by BOM and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), the national science agency, predicts temperatures rising across the country by between 0.6˚C and 1.5C by 2030, compared with the rise of 0.6˚C between 1910 and 1990.

The report says: “Data and analysis from BOM and CSIRO show further warming of the atmosphere and oceans in the Australian region. . . this warming has seen Australia experiencing warm weather and extreme heat, and fewer cool extremes.

“There has been an increase in extreme fire weather, and a longer fire season, across large parts of Australia.” – Climate News Network

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Solar dimming reflects complexity of climate change

Solar dimming reflects complexity of climate change

Reduced monsoon rainfall and increased river flow are two extremes that new research has linked to man-made impacts on climate caused by air pollution.

LONDON, 13 October, 2014 − Two separate studies have confirmed the extent of human influence on climate change – and, for once, carbon dioxide is not the usual suspect.

One team has just found that air pollution dimmed the skies of northern Europe, reflected sunlight back into space, reduced evaporation, and increased river flow.

The second group reports that similar aerosol pollution had a quite different effect on the Asian monsoons: in the second half of the 20th century, the darkening skies reduced temperatures and cut the summer monsoon rainfall by 10%.

The two seemingly contradictory findings underscore two clear conclusions. One is that climate science is complex. The other is that human activity clearly influences the climate in different ways.

Worldwide concern

Both studies are concerned with an era when there was, worldwide, more concern about choking smog, sulphuric aerosol discharges and acid rain than about man-made global warming. They also both match complex computer simulation with observed changes in climate during the second half of the 20th century

Nicola Gedney, a senior scientist at the UK’s Meteorological Office, and colleagues report in Nature Geoscience that she and colleagues looked at the growth in aerosol pollution, especially in the Oder river catchment area of central-eastern Europe, that followed the increased burning of sulphurous coal in Europe right up till the late 1970s.

The consequence of that burning was a reduction in sunlight over the hemisphere. But this began to reverse with clean air legislation and a widespread switch to cleaner fuels. River flows, which had been on the increase, were reduced.

“We estimate that, in the most polluted central Europe river basin, this effect led to an increase in river flow of up to 25% when the aerosol levels were at their peak, around 1980,” Dr Gedney said. “With water shortages likely to be one of the biggest impacts of climate change in the future, these findings are important in making projections.”

Aerosol pollution

Meanwhile, a group led by Debbie Polson, a researcher in the University of Edinburgh’s School of Geosciences, Scotland, focused on aerosol pollution and the Asian summer monsoons, which provide four-fifths of the annual rainfall of the Indian subcontinent.

They report in Geophysical Research Letters that they calculated annual summer rainfall between 1951 and 2005, used computer simulations to quantify the impact of increasing aerosol emissions and greenhouse gases during that time, and factored in natural variations, such as volcanic discharges.

They found that, overall, levels of rain during the monsoon fell by 10%, and this change could only be explained by the influence of aerosols from car and factory exhausts.

“This study has shown for the first time that the drying of the monsoon over the past 50 years cannot be explained by natural climate variability, and that human activity has played a significant role in altering the seasonal monsoon rainfall on which billions of people depend,” Dr Polson said. – Climate News Network

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Oxford is rewriting ancient weather record books

Oxford is rewriting ancient weather record books

New data added to the unique archive documenting Oxford’s weather since 1767 shows that the university city has just had its second driest September on record – following close on its wettest January.

LONDON, 8 October, 2014 – Several parts of the world like to claim that their unpredictable weather allows you to experience spring, summer, autumn and winter in the space of a single day. The city of Oxford, in the English Midlands, cannot make that boast, but it has broken a surprising number of weather records in a fairly short time.

In its latest bout of meteorological exuberance, Oxford has just had its second driest September since records began almost 250 years ago. It recorded 4.1mm of rainfall over last month, with 1929 the only previous year to have had a month with a lower total − just 2.5mm.

This follows hard on the heels (climatically speaking, at least) of the first month of 2014, which was, by contrast, the wettest January the city has recorded, with total rainfall of 146.9 mm − almost three times the normal and 35 times September’s paltry figure.

Rainiest stretch

Go back a little further, though, for wet weather that really meant business: the nine months from 1 April to 31 December 2012 proved the rainiest nine-month stretch in Oxford’s recorded experience.

Yet the people of Oxford might at that point have been lulled into expectations of balmier weather, because 2011 had turned out to be the city’s joint second-warmest year on record. Six of the top 10 warmest years recorded have occurred since 2000, the warmest being 2006.

Oxford, home of the oldest university in the English-speaking world, knows the details of its weather peaks and troughs so well because it possesses a unique archive.

The Radcliffe Meteorological Station, based at Oxford University’s Green Templeton College and maintained by the university’s School of Geography and the Environment, holds the longest series of temperature and rainfall records for one site in Britain, with records dating back to 1767.

Of nearly 3,000 monthly records since Oxford’s measurements began, only 30 have been drier than last month. This puts September 2014 in the top 1% of the city’s driest ever months.

Dr Ian Ashpole, who collects the daily measurements for Radcliffe, said of the latest record to fall: “Based on analysis of variability around the mean September rainfall over the last 248 years, we can say that no Septembers since 2000 have been unusually wet, but three have been unusually dry.”

Emerging trend

Only one of the other 30 driest months has occurred in the autumn (September to November); 14 have been in spring (March to May), eight in summer (June to August), and the remaining seven during the winter. Four of the driest months have occurred this century.

This year’s September record may be part of an emerging trend in the month since 2000. The 248-year long-term average for September is 60mm, but since the turn of the century 12 have been below this average, including six under 50% of expected rainfall. Only two years have been above the 60mm average − 2008 (72.9mm) and 2006 (90.8mm).

September 2014’s temperature was not quite as extreme as the low rainfall, but still came in at equal seventh (with 1998) at 15.9°C, compared with the long-term average of 13.7°C. Five of the warmest eight Septembers since 1767 have been recorded since 1998.

However, the data from Radcliffe applies only to the city of Oxford and a short distance around it, and can tell us nothing about weather elsewhere in the UK or further afield. – Climate News Network

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Warming will leave drought-hit California reeling

Warming will leave drought-hit California reeling

Researchers in the US warn that climate change could worsen California droughts by drastically reducing water flow from the Sierra Nevada mountains − and also threatens the extinction of a rare species of fish.

LONDON, 16 September, 2014 − Things could soon get worse for drought-hit California. New research predicts that, by the close of the century, global warming could have reduced the flow of water from the Sierra Nevada mountains by at least a quarter.

Michael Goulden, associate professor of earth system science at the University of California Irvine, and Roger Bales, director of the Sierra Nevada Research Institute at the University of California Merced, publish their alarming findings in the Proceedings of the National Academy of Sciences.

Plant growth

Their research looked not at the long-term projections for precipitation in the US south-west, but simply at the effect of higher average temperatures on plant growth.

Mountains in many ways mimic hemispheres: just as trees become more stunted at higher latitudes, so they get smaller and less frequent at higher altitudes. Temperature ultimately controls plant growth.

But a projected warming of 4.1°C by 2100 would make a big difference to plant growth in the Arctic tundra and around the present alpine treeline everywhere in the world.

The scientists contemplated snow and rain conditions in the King’s River Basin in the Sierra Nevada range. They looked at how much flows downstream to local communities, and how much goes back into the atmosphere as water vapour. Then they did their sums.

They calculated that the 4.1°C temperature rise in the region would increase the density of vegetation at high elevations, with a 28% increase in evapotranspiration − the process that draws water up through the roots to the leaves, and then releases it as vapour through the pores. And what was true for one river basin, they thought, should be true for the whole area. River run-off could drop by 26%.

“Scientists have recognised for a while that something like this was possible, but no one has been able to quantify whether it could be a big effect,” said Professor Goulden. “It’s clear that this could be a big effect of climate warming and that managers need to recognise and plan for the possibility of increased water losses from forest evaporation.”

Endangered fish

MEANWHILE, climate change threatens to wipe out an endangered species of fish in a remote area of Nevada.

The Devils Hole pupfish (Cyprinodon diabolis) is not just rare, it is very rare: the population has fallen as low as 35 individuals. It lives in the geothermally-warmed waters of a limestone cavern in the Devils Hole in the Mojave desert, and its existence was probably always precarious. The fish are little more than 2cms long, iridescent blue, and they have made their home in the upper 25 metres of the cavern’s waters for at least 10,000 years.

Devils Hole pupfish are only 2cms long Image: Nevada Fish & Wildlife Office

Devils Hole pupfish are only 2cms long
Image: Nevada Fish & Wildlife Office via Wikimedia Commons

But Mark Hausner, a hydrogeologist at the Desert Research Institute in Las Vegas, Nevada, and colleagues report in the journal Water Resources Research that there is only a 10-week window in which the water temperatures are optimal, and there is enough food available, for new larvae to hatch.

Climate change is bringing the already-warm water to dangerous temperature levels, and this has already shortened by at least one week the brief opportunity to restore the population. When counts began in 1972, there were more than 500 of the fish. A decade ago there were 171, and at the last count there were only 92.

“This is a fish that does live in a fishbowl, an incredibly hostile fishbowl, and you can’t move the fishbowl,” said one of the report’s authors, Scott Tyler, professor in the Department of Geological Sciences and Engineering at the University of Nevada, Reno. “This is a species that can’t adapt or change or leave to go to a better environment.” − Climate News Network

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Drought bites as Amazon’s ‘flying rivers’ dry up

Drought bites as Amazon’s ‘flying rivers’ dry up

Scientists in Brazil believe the loss of billions of litres of water released as vapour clouds by Amazon rainforest trees is the result of continuing deforestation and climate change – leading to devastating drought.

SÃO PAULO, 14 September, 2014 − The unprecedented drought now affecting São Paulo, South America’s giant metropolis, is believed to be caused by the absence of the “flying rivers” − the vapour clouds from the Amazon that normally bring rain to the centre and south of Brazil.

Some Brazilian scientists say the absence of rain that has dried up rivers and reservoirs in central and southeast Brazil is not just a quirk of nature, but a change brought about by a combination of the continuing deforestation of the Amazon and global warming.

This combination, they say, is reducing the role of the Amazon rainforest as a giant “water pump”, releasing billions of litres of humidity from the trees into the air in the form of vapour.

Meteorologist Jose Marengo, a member of the Intergovernmental Panel on Climate Change, first coined the phrase “flying rivers” to describe these massive volumes of vapour that rise from the rainforest, travel west, and then − blocked by the Andes − turn south.

Satellite images from the Centre for Weather Forecasts and Climate Research of Brazil’s National Space Research Institute (INPE) clearly show that, during January and February this year, the flying rivers failed to arrive, unlike the previous five years.

Alarming proportions

Deforestation all over Brazil has reached alarming proportions: 22% of the Amazon rainforest (an area larger than Portugal, Italy and Germany combined), 47% of the Cerrado in central Brazil, and 91.5% of the Atlantic forest that used to cover the entire length of the coastal area.

Latest figures from Deter, the Real Time Deforestation Detection System based on high frequency satellite images used by INPE, show that, after falling for two years, Amazon deforestation rose again by 10% between August 2013 and July 2014. The forest is being cleared for logging and farming.

Tocantins, Pará and Mato Grosso, three states in the Greater Amazon region that have suffered massive deforestation, are all registering higher average temperatures.

As long ago as 2009, Antonio Nobre, one of Brazil’s leading climate scientists, warned that, without the “flying rivers”, the area that produces 70% of South America’s GNP would be desert.

In an interview with the journal Valor Economica, he said: “Destroying the Amazon to advance the agricultural frontier is like shooting yourself in the foot. The Amazon is a gigantic hydrological pump that brings the humidity of the Atlantic Ocean into the continent and guarantees the irrigation of the region.”

“Of course, we need agriculture,” he said. “But without trees there would be no water, and without water there is no food.

“A tonne of soy takes several tonnes of water to produce. When we export soy we are exporting fresh water to countries that don’t have this rain and can’t produce. It is the same with cotton, with ethanol. Water is the main agricultural input. If it weren’t, the Sahara would be green, because it has extremely fertile soil.”

Underestimated

Like other climate scientists, Nobre thinks the role of the Amazon rainforest in producing rain has been underestimated. In a single day, the Amazon region evaporates 20 billion tonnes of vapour − more than the 17 million tonnes of water that the Amazon river discharges each day into the Atlantic.

“A big tree with a crown 20 metres across evaporates up to 300 litres a day, whereas one square metre of ocean evaporates exactly one square metre,” he said. “One square metre of forest can contain eight or 10 metres of leaves, so it evaporates eight or 10 times more than the ocean. This flying river, which rises into the atmosphere in the form of vapour, is bigger than the biggest river on the Earth.”

The fear is that if the Amazon rainforest continues to be depleted at the present rate, events like the unprecedented drought of 2010 will occur more often. The fires set by farmers to clear areas for planting or for cattle-raising make it more vulnerable.

Nobre explained: “The smoke from forest fires introduces too many particles into the atmosphere, dries the clouds, and they don’t rain. During the dry period, of the fires, the forest always maintained a little rain that left it humid and non-flammable, but now two months go by without rain, the forest gets very dry, and the fire gets into it. Amazon trees, unlike those of the Cerrado, have no resistance to fire.”

Nobre’s warning in 2009 was that if deforestation did not stop, there would be a catastrophe in five or six years time. Five years on, his words are now proving to be prophetic as São Paulo and all Brazil’s centre and southeast suffer their worst ever drought, with devastating effects on agriculture, energy and domestic water supplies. – Climate News Network

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