Tag Archives: Prehistory

Ancient ice-free polar forest could soon return

An ice-free polar forest once flourished, helped by enough heat and ample greenhouse gas. It could come back.

LONDON, 10 April, 2020 – Many millions of years ago, the southern continent wasn’t frozen at all, but basked in heat balmy enough for an ice-free polar forest to thrive. And ancient pre-history could repeat itself.

Climate scientists can tell you what the world could be like were today’s greenhouse gas concentrations to triple – which they could do if humans go on clearing tropical forests and burning fossil fuels.

They know because, 90 million years ago, the last time when carbon dioxide levels in the atmosphere went past the 1200 ppm (parts per million) mark, sea levels were 170 metres higher than today and the world was so warm that dense forests grew in what is now Antarctica.

At latitude 82 South, a region where the polar night lasts for four months, there was no icecap. Instead, the continental rocks were colonised by conifer forest, with a mix of tree ferns and an understorey of flowering shrubs.

Even though at that latitude the midday sun would have been relatively low in the sky, and the forests would have had to survive sustained winter darkness for a dozen weeks or more, average temperatures would have been that of modern day Tasmania, and a good 2C° warmer than modern Germany.

“Even during months of darkness, swampy temperate forests were able to grow close to the South Pole, revealing an even warmer climate than we expected”

German and British researchers report in the journal Nature that they took a closer look at a sequence of strangely-coloured mudstone in a core drilled 30 metres below the bottom of the sea floor, off West Antarctica.

The section of sediment had been preserved from the mid-Cretaceous, around 90 million years ago, in a world dominated by dinosaurs. By then, the first mammals may have evolved, the grasses were about to emerge, and seasonal flowering plants had begun to colonise a planet dominated for aeons by evergreens.

And in the preserved silt were pollens, spores, tangled roots and other plant material so well preserved that the researchers could not just identify the plant families, but even take a guess at parallels with modern forests. Before their eyes was evidence of something like the modern rainforests of New Zealand’s South Island, but deep inside the Antarctic Circle.

“The preservation of this 90 million-year-old forest is exceptional, but even more surprising is the world it reveals,” said Tina van de Flierdt, of Imperial College London.

“Even during months of darkness, swampy temperate forests were able to grow close to the South Pole, revealing an even warmer climate than we expected.”

British rain levels

Somewhere between 115 and 85 million years ago, the whole world was a lot hotter: in the tropics temperatures reached 35°C and the average temperature of that part of the Antarctic was 13°C. This is at least two degrees higher than the average temperature for modern Germany.

Average temperatures in summer went up to 18.5°C, and the water temperatures in the swamps and rivers tipped 20°C, only 900 kms from the then South Pole. Modern Antarctica is classed as desert, with minimal precipitation: then it would have seen 1120 mm a year. People from southwestern Scotland or parts of Wales would have felt at home.

It is an axiom of earth science that the present is key to the past: if such forests today can flourish at existing temperatures, then the same must have been true in the deep past.

So climate scientists from the start have taken a close interest in the evidence of intensely warm periods in the fossil record: a mix of plant and animal remains, the ratio of chemical isotopes preserved in rock, and even the air bubbles trapped in deep ice cores can help them reconstruct the temperatures, the composition of the atmosphere and the rainfall of, for example, the warmest periods of the Pliocene, when carbon dioxide levels in the atmosphere tipped the 1000 ppm mark, and average planetary temperatures rose by 9°C.

Prehistoric encore approaching?

In the past century, atmospheric CO2 levels have swollen from 285 ppm to more than 400 ppm, and the planetary thermometer has already crept up by 1°C above the level for most of human history. If human economies continue burning fossil fuels at an ever-increasing rate, the conditions that prevailed 56 million years ago could return by 2159.

The Cretaceous evidence will help climate scientists calibrate their models of a world in which greenhouse gas emissions go on rising.

“Before our study, the general assumption was that the global carbon dioxide concentration in the Cretaceous was roughly 1000 ppm,” said Johann Klages, of the Alfred Wegener Institute centre for polar and marine research in Germany, who led the study.

“But in our model-based experiments, it took concentration levels of 1120 to 1680 ppm to reach the average temperatures back then in Antarctica.” – Climate News Network

An ice-free polar forest once flourished, helped by enough heat and ample greenhouse gas. It could come back.

LONDON, 10 April, 2020 – Many millions of years ago, the southern continent wasn’t frozen at all, but basked in heat balmy enough for an ice-free polar forest to thrive. And ancient pre-history could repeat itself.

Climate scientists can tell you what the world could be like were today’s greenhouse gas concentrations to triple – which they could do if humans go on clearing tropical forests and burning fossil fuels.

They know because, 90 million years ago, the last time when carbon dioxide levels in the atmosphere went past the 1200 ppm (parts per million) mark, sea levels were 170 metres higher than today and the world was so warm that dense forests grew in what is now Antarctica.

At latitude 82 South, a region where the polar night lasts for four months, there was no icecap. Instead, the continental rocks were colonised by conifer forest, with a mix of tree ferns and an understorey of flowering shrubs.

Even though at that latitude the midday sun would have been relatively low in the sky, and the forests would have had to survive sustained winter darkness for a dozen weeks or more, average temperatures would have been that of modern day Tasmania, and a good 2C° warmer than modern Germany.

“Even during months of darkness, swampy temperate forests were able to grow close to the South Pole, revealing an even warmer climate than we expected”

German and British researchers report in the journal Nature that they took a closer look at a sequence of strangely-coloured mudstone in a core drilled 30 metres below the bottom of the sea floor, off West Antarctica.

The section of sediment had been preserved from the mid-Cretaceous, around 90 million years ago, in a world dominated by dinosaurs. By then, the first mammals may have evolved, the grasses were about to emerge, and seasonal flowering plants had begun to colonise a planet dominated for aeons by evergreens.

And in the preserved silt were pollens, spores, tangled roots and other plant material so well preserved that the researchers could not just identify the plant families, but even take a guess at parallels with modern forests. Before their eyes was evidence of something like the modern rainforests of New Zealand’s South Island, but deep inside the Antarctic Circle.

“The preservation of this 90 million-year-old forest is exceptional, but even more surprising is the world it reveals,” said Tina van de Flierdt, of Imperial College London.

“Even during months of darkness, swampy temperate forests were able to grow close to the South Pole, revealing an even warmer climate than we expected.”

British rain levels

Somewhere between 115 and 85 million years ago, the whole world was a lot hotter: in the tropics temperatures reached 35°C and the average temperature of that part of the Antarctic was 13°C. This is at least two degrees higher than the average temperature for modern Germany.

Average temperatures in summer went up to 18.5°C, and the water temperatures in the swamps and rivers tipped 20°C, only 900 kms from the then South Pole. Modern Antarctica is classed as desert, with minimal precipitation: then it would have seen 1120 mm a year. People from southwestern Scotland or parts of Wales would have felt at home.

It is an axiom of earth science that the present is key to the past: if such forests today can flourish at existing temperatures, then the same must have been true in the deep past.

So climate scientists from the start have taken a close interest in the evidence of intensely warm periods in the fossil record: a mix of plant and animal remains, the ratio of chemical isotopes preserved in rock, and even the air bubbles trapped in deep ice cores can help them reconstruct the temperatures, the composition of the atmosphere and the rainfall of, for example, the warmest periods of the Pliocene, when carbon dioxide levels in the atmosphere tipped the 1000 ppm mark, and average planetary temperatures rose by 9°C.

Prehistoric encore approaching?

In the past century, atmospheric CO2 levels have swollen from 285 ppm to more than 400 ppm, and the planetary thermometer has already crept up by 1°C above the level for most of human history. If human economies continue burning fossil fuels at an ever-increasing rate, the conditions that prevailed 56 million years ago could return by 2159.

The Cretaceous evidence will help climate scientists calibrate their models of a world in which greenhouse gas emissions go on rising.

“Before our study, the general assumption was that the global carbon dioxide concentration in the Cretaceous was roughly 1000 ppm,” said Johann Klages, of the Alfred Wegener Institute centre for polar and marine research in Germany, who led the study.

“But in our model-based experiments, it took concentration levels of 1120 to 1680 ppm to reach the average temperatures back then in Antarctica.” – Climate News Network

Carbon dioxide triggered ancient mass die-off

The biggest extinction ever known on Earth resulted from oceans turned acid by CO2, the main gas driving human-caused climate change today. LONDON, 16 April, 2015 − Scientists have identified the lethal agency that caused the single most catastrophic event in the history of life on Earth. The mass extinction at the boundary of the Permian and Triassic eras 252 million years ago was caused by the acidification of the world’s oceans, as a consequence of an increase in atmospheric carbon dioxide. The Permian Extinction – sometimes called “the Great Dying” – seemed to all but obliterate life in the oceans, and perhaps on land. More than 90% of all species disappeared, more than 80% of all genera, and more than 50% of all marine families were extinguished in one prolonged calamity. All life on Earth today has descended from the few survivors of this far-off episode. Palaeontologists, geologists, climate scientists and astronomers have all speculated on the probable cause. The latest and most confident analysis is based on a new study of ancient marine sediments and delivers obvious parallels with processes that are – for different reasons − occurring again today. Matthew Clarkson of the University of Edinburgh in Scotland (but now at the University of Otago in New Zealand) and colleagues report in the journal Science that they examined limestone from the United Arab Emirates and found, in the isotope ratios of the element boron, evidence of ocean acidity in carbonate rocks that were laid down as sediment at the bottom of the ocean 250 million years ago. A change in the isotope ratios, they calculated, would have indicated a significant shift in seawater chemistry.

“This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions”

Over the last 40 years, researchers have introduced a whole suite of plausible triggers for the Permian extinction, but at last one team had clear evidence of increased atmospheric carbon, probably from a prolonged and convulsive series of volcanic eruptions that gave rise to vast, ancient geological formations now known as the Siberian Traps. “Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now”, said Dr Clarkson. “This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions.” There has been recent evidence that this present change in the pH of ocean waters (pH is a measure of its acidity) as a consequence of fossil fuel combustion in the last two centuries has already disturbed the behaviour of some fish species, threatened to affect oyster fisheries and coral reefs, and even to alter whole ocean ecosystems. The changes in the Permian were not sudden: ecosystems already seriously under stress because of lack of oxygen or rising temperatures were then dramatically affected by discharges of carbon dioxide that were probably much greater than all the modern world’s existing fossil fuel reserves could deliver. As the oceans became more acidic, many species were extinguished forever: among them the trilobites. The whole chain of events took 60,000 years. Humans have been burning fossil fuels for only 200 years, but, the researchers point out, in the Permian crisis, carbon was probably being released into the atmosphere at the rate of about 2.4 billion tons a year. Right now, humans are estimated to be releasing carbon from fossil fuels at the rate of 10 billion tons a year. − Climate News Network

The biggest extinction ever known on Earth resulted from oceans turned acid by CO2, the main gas driving human-caused climate change today. LONDON, 16 April, 2015 − Scientists have identified the lethal agency that caused the single most catastrophic event in the history of life on Earth. The mass extinction at the boundary of the Permian and Triassic eras 252 million years ago was caused by the acidification of the world’s oceans, as a consequence of an increase in atmospheric carbon dioxide. The Permian Extinction – sometimes called “the Great Dying” – seemed to all but obliterate life in the oceans, and perhaps on land. More than 90% of all species disappeared, more than 80% of all genera, and more than 50% of all marine families were extinguished in one prolonged calamity. All life on Earth today has descended from the few survivors of this far-off episode. Palaeontologists, geologists, climate scientists and astronomers have all speculated on the probable cause. The latest and most confident analysis is based on a new study of ancient marine sediments and delivers obvious parallels with processes that are – for different reasons − occurring again today. Matthew Clarkson of the University of Edinburgh in Scotland (but now at the University of Otago in New Zealand) and colleagues report in the journal Science that they examined limestone from the United Arab Emirates and found, in the isotope ratios of the element boron, evidence of ocean acidity in carbonate rocks that were laid down as sediment at the bottom of the ocean 250 million years ago. A change in the isotope ratios, they calculated, would have indicated a significant shift in seawater chemistry.

“This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions”

Over the last 40 years, researchers have introduced a whole suite of plausible triggers for the Permian extinction, but at last one team had clear evidence of increased atmospheric carbon, probably from a prolonged and convulsive series of volcanic eruptions that gave rise to vast, ancient geological formations now known as the Siberian Traps. “Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now”, said Dr Clarkson. “This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions.” There has been recent evidence that this present change in the pH of ocean waters (pH is a measure of its acidity) as a consequence of fossil fuel combustion in the last two centuries has already disturbed the behaviour of some fish species, threatened to affect oyster fisheries and coral reefs, and even to alter whole ocean ecosystems. The changes in the Permian were not sudden: ecosystems already seriously under stress because of lack of oxygen or rising temperatures were then dramatically affected by discharges of carbon dioxide that were probably much greater than all the modern world’s existing fossil fuel reserves could deliver. As the oceans became more acidic, many species were extinguished forever: among them the trilobites. The whole chain of events took 60,000 years. Humans have been burning fossil fuels for only 200 years, but, the researchers point out, in the Permian crisis, carbon was probably being released into the atmosphere at the rate of about 2.4 billion tons a year. Right now, humans are estimated to be releasing carbon from fossil fuels at the rate of 10 billion tons a year. − Climate News Network

Climate change 'helped to end monsoon 4,000 years ago'

FOR IMMEDIATE RELEASE
Drought appears to have played a significant part in the collapse of a vibrant community in south-west Asia several thousand years ago, British researchers say – with lessons for us today.

LONDON, 27 February – Climate change can seriously damage a civilisation. An “abrupt weakening” of the summer monsoon in north-west India accompanied the decline of the great cities of the Indus valley more than 4,000 years ago, according to new research by British scientists.

They analysed the oxygen isotopes in snail shells preserved in ancient lake sediments to build up a picture of rainfall patterns in prehistory, and found the first direct evidence that sustained drought contributed to the collapse of a great Bronze Age civilisation, they report in the journal Geology.

The Indus or Harappan civilisation – after Harappa, one of the five great ancient settlements of what is now Pakistan and western India – was marked by the world’s first “megacities”, concentrations of population in built-up areas that covered more than 80 hectares.

“They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East,” said Cameron Petrie of the University of Cambridge. “But by the mid-second millennium BC, all the great urban centres had dramatically reduced in size or been abandoned.”

The finding links the decline of the Indus civilisation to what now seems a much greater scale event: the failure of Early Bronze Age civilisation in Greece and Crete, the weakening of the Old Kingdom in Egypt, and the crumbling of the Akkadian Empire in Mesopotamia.

Common factor

Researchers last year used pollen grain sediments in an old lake bed in Cyprus to build up a picture of sustained environmental decline that accompanied the collapse of the civilisations linked with Mycenae in Greece and Knossos in Crete. In all cases, there must have been a number of factors at work, but common to them all was a pattern of drought.

Without water crops fail, populations fall and concentrations of people must disperse. Archaeological evidence in the north-west Indian sub-continent has told a story of dispersal. Palaeontological evidence from an old lake bed has confirmed the picture of a changing climate.

“We think we now have a really strong indication that a major climate change event occurred in the area where a large number of Indus settlements were situated,” said David Hodell, an earth scientist at Cambridge, and one of the authors.

“Taken with other evidence from Meghalaya in north-east India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.”

The authors collected shells of the water snail Melanoides tuberculata from the sediments on an ancient lake, Kotla Dahar in Haryana, India. The changes in oxygen isotope ratios over a period of thousands of years told the researchers a story of a deep lake that became a shallower one, as evaporation accelerated and water supplies dwindled, and then all but disappeared, with an abrupt weakening of the monsoons that lasted around 200 years.

Syrian parallel?

Oxygen occurs in two isotopes: water molecules containing the lighter variant evaporate at a predictably faster rate than the heavier version. In a drought, the ratios of the heavier version increase, and this increase is preserved in the calcium carbonate of the snail shells, which can in turn be dated by radiocarbon measurements.

Archaeological evidence suggests that around the time of the 200-year drought, streets that had once been well-maintained started to fill with rubbish, craftsmanship seemed to become less sophisticated, and the locations of settlements changed.

“It is essential to understand the link between human settlement, water resources and landscape in antiquity,” said Dr Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.”

Simultaneously, a French academic has argued that extended drought may have played a role in the crisis in Syria right now. Francesca de Chatel of Radboud University in the Netherlands writes in Middle Eastern Studies that in her opinion the bloodshed and turmoil in Syria is the culmination of 50 years of sustained mismanagement of water and land resources, capped by a severe drought during the years 2006-2010.

She argues “It was not the drought per se, but rather the government’s failure to respond to the ensuing humanitarian crisis that formed one of the triggers of the uprising, feeding a discontent that had long been simmering in rural areas.” – Climate News Network

FOR IMMEDIATE RELEASE
Drought appears to have played a significant part in the collapse of a vibrant community in south-west Asia several thousand years ago, British researchers say – with lessons for us today.

LONDON, 27 February – Climate change can seriously damage a civilisation. An “abrupt weakening” of the summer monsoon in north-west India accompanied the decline of the great cities of the Indus valley more than 4,000 years ago, according to new research by British scientists.

They analysed the oxygen isotopes in snail shells preserved in ancient lake sediments to build up a picture of rainfall patterns in prehistory, and found the first direct evidence that sustained drought contributed to the collapse of a great Bronze Age civilisation, they report in the journal Geology.

The Indus or Harappan civilisation – after Harappa, one of the five great ancient settlements of what is now Pakistan and western India – was marked by the world’s first “megacities”, concentrations of population in built-up areas that covered more than 80 hectares.

“They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East,” said Cameron Petrie of the University of Cambridge. “But by the mid-second millennium BC, all the great urban centres had dramatically reduced in size or been abandoned.”

The finding links the decline of the Indus civilisation to what now seems a much greater scale event: the failure of Early Bronze Age civilisation in Greece and Crete, the weakening of the Old Kingdom in Egypt, and the crumbling of the Akkadian Empire in Mesopotamia.

Common factor

Researchers last year used pollen grain sediments in an old lake bed in Cyprus to build up a picture of sustained environmental decline that accompanied the collapse of the civilisations linked with Mycenae in Greece and Knossos in Crete. In all cases, there must have been a number of factors at work, but common to them all was a pattern of drought.

Without water crops fail, populations fall and concentrations of people must disperse. Archaeological evidence in the north-west Indian sub-continent has told a story of dispersal. Palaeontological evidence from an old lake bed has confirmed the picture of a changing climate.

“We think we now have a really strong indication that a major climate change event occurred in the area where a large number of Indus settlements were situated,” said David Hodell, an earth scientist at Cambridge, and one of the authors.

“Taken with other evidence from Meghalaya in north-east India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.”

The authors collected shells of the water snail Melanoides tuberculata from the sediments on an ancient lake, Kotla Dahar in Haryana, India. The changes in oxygen isotope ratios over a period of thousands of years told the researchers a story of a deep lake that became a shallower one, as evaporation accelerated and water supplies dwindled, and then all but disappeared, with an abrupt weakening of the monsoons that lasted around 200 years.

Syrian parallel?

Oxygen occurs in two isotopes: water molecules containing the lighter variant evaporate at a predictably faster rate than the heavier version. In a drought, the ratios of the heavier version increase, and this increase is preserved in the calcium carbonate of the snail shells, which can in turn be dated by radiocarbon measurements.

Archaeological evidence suggests that around the time of the 200-year drought, streets that had once been well-maintained started to fill with rubbish, craftsmanship seemed to become less sophisticated, and the locations of settlements changed.

“It is essential to understand the link between human settlement, water resources and landscape in antiquity,” said Dr Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.”

Simultaneously, a French academic has argued that extended drought may have played a role in the crisis in Syria right now. Francesca de Chatel of Radboud University in the Netherlands writes in Middle Eastern Studies that in her opinion the bloodshed and turmoil in Syria is the culmination of 50 years of sustained mismanagement of water and land resources, capped by a severe drought during the years 2006-2010.

She argues “It was not the drought per se, but rather the government’s failure to respond to the ensuing humanitarian crisis that formed one of the triggers of the uprising, feeding a discontent that had long been simmering in rural areas.” – Climate News Network

Climate change ‘helped to end monsoon 4,000 years ago’

FOR IMMEDIATE RELEASE Drought appears to have played a significant part in the collapse of a vibrant community in south-west Asia several thousand years ago, British researchers say – with lessons for us today. LONDON, 27 February – Climate change can seriously damage a civilisation. An “abrupt weakening” of the summer monsoon in north-west India accompanied the decline of the great cities of the Indus valley more than 4,000 years ago, according to new research by British scientists. They analysed the oxygen isotopes in snail shells preserved in ancient lake sediments to build up a picture of rainfall patterns in prehistory, and found the first direct evidence that sustained drought contributed to the collapse of a great Bronze Age civilisation, they report in the journal Geology. The Indus or Harappan civilisation – after Harappa, one of the five great ancient settlements of what is now Pakistan and western India – was marked by the world’s first “megacities”, concentrations of population in built-up areas that covered more than 80 hectares. “They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East,” said Cameron Petrie of the University of Cambridge. “But by the mid-second millennium BC, all the great urban centres had dramatically reduced in size or been abandoned.” The finding links the decline of the Indus civilisation to what now seems a much greater scale event: the failure of Early Bronze Age civilisation in Greece and Crete, the weakening of the Old Kingdom in Egypt, and the crumbling of the Akkadian Empire in Mesopotamia.

Common factor

Researchers last year used pollen grain sediments in an old lake bed in Cyprus to build up a picture of sustained environmental decline that accompanied the collapse of the civilisations linked with Mycenae in Greece and Knossos in Crete. In all cases, there must have been a number of factors at work, but common to them all was a pattern of drought. Without water crops fail, populations fall and concentrations of people must disperse. Archaeological evidence in the north-west Indian sub-continent has told a story of dispersal. Palaeontological evidence from an old lake bed has confirmed the picture of a changing climate. “We think we now have a really strong indication that a major climate change event occurred in the area where a large number of Indus settlements were situated,” said David Hodell, an earth scientist at Cambridge, and one of the authors. “Taken with other evidence from Meghalaya in north-east India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.” The authors collected shells of the water snail Melanoides tuberculata from the sediments on an ancient lake, Kotla Dahar in Haryana, India. The changes in oxygen isotope ratios over a period of thousands of years told the researchers a story of a deep lake that became a shallower one, as evaporation accelerated and water supplies dwindled, and then all but disappeared, with an abrupt weakening of the monsoons that lasted around 200 years.

Syrian parallel?

Oxygen occurs in two isotopes: water molecules containing the lighter variant evaporate at a predictably faster rate than the heavier version. In a drought, the ratios of the heavier version increase, and this increase is preserved in the calcium carbonate of the snail shells, which can in turn be dated by radiocarbon measurements. Archaeological evidence suggests that around the time of the 200-year drought, streets that had once been well-maintained started to fill with rubbish, craftsmanship seemed to become less sophisticated, and the locations of settlements changed. “It is essential to understand the link between human settlement, water resources and landscape in antiquity,” said Dr Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.” Simultaneously, a French academic has argued that extended drought may have played a role in the crisis in Syria right now. Francesca de Chatel of Radboud University in the Netherlands writes in Middle Eastern Studies that in her opinion the bloodshed and turmoil in Syria is the culmination of 50 years of sustained mismanagement of water and land resources, capped by a severe drought during the years 2006-2010. She argues “It was not the drought per se, but rather the government’s failure to respond to the ensuing humanitarian crisis that formed one of the triggers of the uprising, feeding a discontent that had long been simmering in rural areas.” – Climate News Network

FOR IMMEDIATE RELEASE Drought appears to have played a significant part in the collapse of a vibrant community in south-west Asia several thousand years ago, British researchers say – with lessons for us today. LONDON, 27 February – Climate change can seriously damage a civilisation. An “abrupt weakening” of the summer monsoon in north-west India accompanied the decline of the great cities of the Indus valley more than 4,000 years ago, according to new research by British scientists. They analysed the oxygen isotopes in snail shells preserved in ancient lake sediments to build up a picture of rainfall patterns in prehistory, and found the first direct evidence that sustained drought contributed to the collapse of a great Bronze Age civilisation, they report in the journal Geology. The Indus or Harappan civilisation – after Harappa, one of the five great ancient settlements of what is now Pakistan and western India – was marked by the world’s first “megacities”, concentrations of population in built-up areas that covered more than 80 hectares. “They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East,” said Cameron Petrie of the University of Cambridge. “But by the mid-second millennium BC, all the great urban centres had dramatically reduced in size or been abandoned.” The finding links the decline of the Indus civilisation to what now seems a much greater scale event: the failure of Early Bronze Age civilisation in Greece and Crete, the weakening of the Old Kingdom in Egypt, and the crumbling of the Akkadian Empire in Mesopotamia.

Common factor

Researchers last year used pollen grain sediments in an old lake bed in Cyprus to build up a picture of sustained environmental decline that accompanied the collapse of the civilisations linked with Mycenae in Greece and Knossos in Crete. In all cases, there must have been a number of factors at work, but common to them all was a pattern of drought. Without water crops fail, populations fall and concentrations of people must disperse. Archaeological evidence in the north-west Indian sub-continent has told a story of dispersal. Palaeontological evidence from an old lake bed has confirmed the picture of a changing climate. “We think we now have a really strong indication that a major climate change event occurred in the area where a large number of Indus settlements were situated,” said David Hodell, an earth scientist at Cambridge, and one of the authors. “Taken with other evidence from Meghalaya in north-east India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.” The authors collected shells of the water snail Melanoides tuberculata from the sediments on an ancient lake, Kotla Dahar in Haryana, India. The changes in oxygen isotope ratios over a period of thousands of years told the researchers a story of a deep lake that became a shallower one, as evaporation accelerated and water supplies dwindled, and then all but disappeared, with an abrupt weakening of the monsoons that lasted around 200 years.

Syrian parallel?

Oxygen occurs in two isotopes: water molecules containing the lighter variant evaporate at a predictably faster rate than the heavier version. In a drought, the ratios of the heavier version increase, and this increase is preserved in the calcium carbonate of the snail shells, which can in turn be dated by radiocarbon measurements. Archaeological evidence suggests that around the time of the 200-year drought, streets that had once been well-maintained started to fill with rubbish, craftsmanship seemed to become less sophisticated, and the locations of settlements changed. “It is essential to understand the link between human settlement, water resources and landscape in antiquity,” said Dr Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.” Simultaneously, a French academic has argued that extended drought may have played a role in the crisis in Syria right now. Francesca de Chatel of Radboud University in the Netherlands writes in Middle Eastern Studies that in her opinion the bloodshed and turmoil in Syria is the culmination of 50 years of sustained mismanagement of water and land resources, capped by a severe drought during the years 2006-2010. She argues “It was not the drought per se, but rather the government’s failure to respond to the ensuing humanitarian crisis that formed one of the triggers of the uprising, feeding a discontent that had long been simmering in rural areas.” – Climate News Network