Chris Turney's Blog, page 2

Why remote Antarctica is so important in a warming world ...

Why remote Antarctica is so important in a warming world Chris Fogwill, Keele University ; Chris Turney, UNSW , and Zoe Robinson, Keele University

Ever since the ancient Greeks speculated a continent must exist in the south polar regions to balance those in the north, Antarctica has been popularly described as remote and extreme. Over the past two centuries, these factors have combined to create, in the human psyche, an almost mythical land – an idea reinforced by tales of heroism and adventure from the Edwardian golden age of “heroic exploration” and pioneers such as Robert Falcon Scott, Roald Amundsen and Ernest Shackleton.

Recent research, however, is casting new light on the importance of the southernmost continent, overturning centuries of misunderstanding and highlighting the role of Antarctica in how our planet works and the role it may play in a future, warmer world.

Heroic exploration, 1913. wiki

What was once thought to be a largely unchanging mass of snow and ice is anything but. Antarctica holds a staggering amount of water. The three ice sheets that cover the continent contain around 70% of our planet’s fresh water, all of which we now know to be vulnerable to warming air and oceans. If all the ice sheets were to melt, Antarctica would raise global sea levels by at least 56m.

Where, when, and how quickly they might melt is a major focus of research. No one is suggesting all the ice sheets will melt over the next century but, given their size, even small losses could have global repercussions. Possible scenarios are deeply concerning: in addition to rising sea levels, meltwater would slow down the world’s ocean circulation, while shifting wind belts may affect the climate in the southern hemisphere.

In 2014, NASA reported that several major Antarctic ice streams, which hold enough water to trigger the equivalent of a one-and-a-half metre sea level rise, are now irreversibly in retreat. With more than 150m people exposed to the threat of sea level rise and sea levels now rising at a faster rate globally than any time in the past 3,000 years, these are sobering statistics for island nations and coastal cities worldwide.

An immediate and acute threat

Recent storm surges following hurricanes have demonstrated that rising sea levels are a future threat for densely populated regions such as Florida and New York. Meanwhile the threat for low-lying islands in areas such as the Pacific is immediate and acute.

Much of the continent’s ice is slow sliding towards the sea. R Bindschadler / wiki

Multiple factors mean that the vulnerability to global sea level rise is geographically variable and unequal, while there are also regional differences in the extremity of sea level rise itself. At present, the consensus of the IPPC 2013 report suggests a rise of between 40 and 80cm over the next century, with Antarctica only contributing around 5cm of this. Recent projections, however, suggest that Antarctic contributions may be up to ten times higher.

Studies also suggest that in a world 1.5-2°C warmer than today we will be locked into millennia of irreversible sea level rise, due to the slow response time of the Antarctic ice sheets to atmospheric and ocean warming.

We may already be living in such a world. Recent evidence shows global temperatures are close to 1.5°C warmer than pre-industrial times and, after the COP23 meeting in Bonn in November, it is apparent that keeping temperature rise within 2°C is unlikely.

So we now need to reconsider future sea level projections given the potential global impact from Antarctica. Given that 93% of the heat from anthropogenic global warming has gone into the ocean, and these warming ocean waters are now meeting the floating margins of the Antarctic ice sheet, the potential for rapid ice sheet melt in a 2°C world is high.

In polar regions, surface temperatures are projected to rise twice as fast as the global average, due to a phenomenon known as polar amplification. However, there is still hope to avoid this sword of Damocles, as studies suggest that a major reduction in greenhouse gases over the next decade would mean that irreversible sea level rise could be avoided. It is therefore crucial to reduce CO₂ levels now for the benefit of future generations, or adapt to a world in which more of our shorelines are significantly redrawn.

This is both a scientific and societal issue. We have choices: technological innovations are providing new ways to reduce CO₂ emissions, and offer the reality of a low-carbon future. This may help minimise sea level rise from Antarctica and make mitigation a viable possibility.

Given what rising sea levels could mean for human societies across the world, we must maintain our longstanding view of Antarctica as the most remote and isolated continent.

Chris Fogwill, Professor of Glaciology and Palaeoclimatology, Keele University; Chris Turney, Professor of Earth Sciences and Climate Change, UNSW, and Zoe Robinson, Reader in Physical Geography and Sustainability/Director of Education for Sustainability, Keele University

This article was originally published on The Conversation. Read the original article.

Revenge served cold: was Scott of the Antarctic sabotaged by his angry deputy?

Revenge served cold: was Scott of the Antarctic sabotaged by his angry deputy? Scott and his team at the geographic South Pole, January 18, 1912. National Library of Australia Chris Turney, UNSW

On February 11, 1913, the world woke to the headline “Death of Captain Scott. Lost with four comrades. The Pole reached. Disaster on the return”. A keenly anticipated, privately funded scientific venture “off the map” had turned to tragedy.

Previous reports had described the polar party of the British Antarctic Expedition striking out confidently just 2.5º latitude from their objective: the geographic South Pole. The journals and letters recovered from the bodies, however, told a tale of heartbreak and desperation: the explorers were shattered to find themselves beaten to the pole by Norwegian rival Roald Amundsen, and weakened terribly during their journey back to base.

Of the five men in Captain Robert F. Scott’s party, Petty Officer Edgar Evans was the first to die, while descending from the high-altitude Antarctic Plateau. Then, while searching in vain on the vast Ross Ice Shelf for the dog sleds ordered to speed their return to base, Captain Lawrence “Titus” Oates realised that his ever-slowing pace was threatening the others, and famously walked out into a blizzard with the parting words: “I am just going outside and may be some time.”

Pushing on with limited supplies, the remaining men (Scott, Dr Edward Wilson and Henry “Birdie” Bowers) found themselves trapped by a nine-day blizzard. All three wrote messages to friends and loved ones while waiting, until eventually their food ran out on about March 29, 1912.

Why did they really die?

Their deaths were put down to the fickleness of Antarctic weather, bad luck or, most controversially, poor leadership on the part of Scott.

But my new research, published in the journal Polar Record, has uncovered new evidence about this ill-fated journey. I have identified major contradictions in the testimony of Scott’s second-in-command, Lieutenant Edward “Teddy” Evans, who survived the expedition after being rejected from Scott’s party.

Was Scott scuppered by Evans?

Evans’s actions raise the possibility that he played a role in the deaths of the five men. Furious at not being included in the attempt on the pole, Evans was returning to base when he collapsed with scurvy. Evans was the only expedition member to develop scurvy, most probably due to his refusal to eat fresh seal meat, a known preventive measure.

His companions Tom Crean and William Lashly heroically saved Evans’s life, a tale made famous in no small measure by expeditioner Apsley Cherry-Garrard’s classic book on the expedition, The Worst Journey in the World.

Foul play over food?

Buried in the British Library, I found a crucial piece of evidence about Evans’s trip back to camp. Seven pages of notes detail meetings held in April 1913 between Lord Curzon, president of the Royal Geographical Society, and Scott’s and Wilson’s widows, both of whom had read their late husbands’ diaries and correspondence.

According to the notes, Kathleen Scott reported that:

Scott’s words in his diary on exhaustion of food & fuel in depots on his return… It appears Lieut Evans – down with Scurvy – and the 2 men with him must on return journey have entered & consumed more than their share.

Several days later, also according to the meeting notes, Oriana Wilson described how:

…there was a passage in her husband’s diary which spoke of the “inexplicable” shortage of fuel & pemmican [sledging ration] on the return journey… This passage however she proposes to show to no one and to keep secret.

Closer examination of diary entries suggest that the food in question went missing from a depot at the southern end of the Ross Ice Shelf. Letters from the time indicate that Curzon immediately shut down the inquiry he was planning to hold. It is not unreasonable to assume that Curzon’s interpretation of events was that Evans was dangerously ill and if he had not taken the food would have also died.

But the account of exactly when Evans fell down with scurvy changed over time. Returning to civilisation in 1912, Evans described in a letter how he was stricken when he was 300 miles from base, a distance confirmed by media interviews from the time.

But by the following year, this figure had changed to 500 miles, a distance also reported in the book Scott’s Last Expedition. This would put the onset of his sickness at the southern end of the Ross Ice Shelf, precisely where the food appears to have gone missing.

Unwittingly, Cherry-Garrard published a substantially embellished version of Lashly’s sledging diary in The Worst Journey in the World, in which Evans’s sickness was shifted one week earlier to align with the public timeline.

Overall, the evidence strongly suggests that Evans took the cached food when he had not yet succumbed to scurvy, possibly because of his anger at having been sent back early and forced to drag his sledge with just two men. The timing of the various pieces evidence suggest that his story was later changed to fit with the idea that he took the food because he was ill.

Disturbingly, Scott’s order to Evans to send the dog sled teams to the southern end of the Ross Ice Shelf does not appear to have been communicated either, fatally slowing the polar party’s return.

Writing from his deathbed, Scott warned: “Teddy Evans is not to be trusted over much, though he means well.”

Given the evidence, this was arguably a generous statement.

Chris Turney, Professor of Earth Sciences and Climate Change, UNSW

This article was originally published on The Conversation. Read the original article.

Revenge served cold: was Scott of the Antarctic sabotaged...

Revenge served cold: was Scott of the Antarctic sabotaged by his angry deputy? Scott and his team at the geographic South Pole, January 18, 1912. National Library of Australia Chris Turney, UNSW

On February 11, 1913, the world woke to the headline “Death of Captain Scott. Lost with four comrades. The Pole reached. Disaster on the return”. A keenly anticipated, privately funded scientific venture “off the map” had turned to tragedy.

Previous reports had described the polar party of the British Antarctic Expedition striking out confidently just 2.5º latitude from their objective: the geographic South Pole. The journals and letters recovered from the bodies, however, told a tale of heartbreak and desperation: the explorers were shattered to find themselves beaten to the pole by Norwegian rival Roald Amundsen, and weakened terribly during their journey back to base.

Of the five men in Captain Robert F. Scott’s party, Petty Officer Edgar Evans was the first to die, while descending from the high-altitude Antarctic Plateau. Then, while searching in vain on the vast Ross Ice Shelf for the dog sleds ordered to speed their return to base, Captain Lawrence “Titus” Oates realised that his ever-slowing pace was threatening the others, and famously walked out into a blizzard with the parting words: “I am just going outside and may be some time.”

Pushing on with limited supplies, the remaining men (Scott, Dr Edward Wilson and Henry “Birdie” Bowers) found themselves trapped by a nine-day blizzard. All three wrote messages to friends and loved ones while waiting, until eventually their food ran out on about March 29, 1912.

Why did they really die?

Their deaths were put down to the fickleness of Antarctic weather, bad luck or, most controversially, poor leadership on the part of Scott.

But my new research, published in the journal Polar Record, has uncovered new evidence about this ill-fated journey. I have identified major contradictions in the testimony of Scott’s second-in-command, Lieutenant Edward “Teddy” Evans, who survived the expedition after being rejected from Scott’s party.

Was Scott scuppered by Evans?

Evans’s actions raise the possibility that he played a role in the deaths of the five men. Furious at not being included in the attempt on the pole, Evans was returning to base when he collapsed with scurvy. Evans was the only expedition member to develop scurvy, most probably due to his refusal to eat fresh seal meat, a known preventive measure.

His companions Tom Crean and William Lashly heroically saved Evans’s life, a tale made famous in no small measure by expeditioner Apsley Cherry-Garrard’s classic book on the expedition, The Worst Journey in the World.

Foul play over food?

Buried in the British Library, I found a crucial piece of evidence about Evans’s trip back to camp. Seven pages of notes detail meetings held in April 1913 between Lord Curzon, president of the Royal Geographical Society, and Scott’s and Wilson’s widows, both of whom had read their late husbands’ diaries and correspondence.

According to the notes, Kathleen Scott reported that:

Scott’s words in his diary on exhaustion of food & fuel in depots on his return… It appears Lieut Evans – down with Scurvy – and the 2 men with him must on return journey have entered & consumed more than their share.

Several days later, also according to the meeting notes, Oriana Wilson described how:

…there was a passage in her husband’s diary which spoke of the “inexplicable” shortage of fuel & pemmican [sledging ration] on the return journey… This passage however she proposes to show to no one and to keep secret.

Closer examination of diary entries suggest that the food in question went missing from a depot at the southern end of the Ross Ice Shelf. Letters from the time indicate that Curzon immediately shut down the inquiry he was planning to hold. It is not unreasonable to assume that Curzon’s interpretation of events was that Evans was dangerously ill and if he had not taken the food would have also died.

But the account of exactly when Evans fell down with scurvy changed over time. Returning to civilisation in 1912, Evans described in a letter how he was stricken when he was 300 miles from base, a distance confirmed by media interviews from the time.

But by the following year, this figure had changed to 500 miles, a distance also reported in the book Scott’s Last Expedition. This would put the onset of his sickness at the southern end of the Ross Ice Shelf, precisely where the food appears to have gone missing.

Unwittingly, Cherry-Garrard published a substantially embellished version of Lashly’s sledging diary in The Worst Journey in the World, in which Evans’s sickness was shifted one week earlier to align with the public timeline.

Overall, the evidence strongly suggests that Evans took the cached food when he had not yet succumbed to scurvy, possibly because of his anger at having been sent back early and forced to drag his sledge with just two men. The timing of the various pieces evidence suggest that his story was later changed to fit with the idea that he took the food because he was ill.

Disturbingly, Scott’s order to Evans to send the dog sled teams to the southern end of the Ross Ice Shelf does not appear to have been communicated either, fatally slowing the polar party’s return.

Writing from his deathbed, Scott warned: “Teddy Evans is not to be trusted over much, though he means well.”

Given the evidence, this was arguably a generous statement.

Chris Turney, Professor of Earth Sciences and Climate Change, UNSW

This article was originally published on The Conversation. Read the original article.

Telling Stories for Science: Shackleton Style

The great American scientist Carl Sagan once remarked ‘If we teach only the findings and products of science — no matter how useful and inspiring they may be—without communicating its critical method, how can the average person possibly distinguish science from pseudoscience?’ Forty years after these words were penned, Sagan’s concern could not be more prescient. We live in an age where ‘alternative facts’ arefast becoming a defendablepoint of view, where expert opinion is now routinely considered as just one point of view. There is clearly a need for a more scientifically literate society, one better versed in critical thinking. But the prognosis is not positive. Across the Western World, countries like the USA, UK and Australia, report an alarming fall in the number of students taking science, technology, engineering and mathematics – the so-called STEM subjects. Sadly, multibillion dollar budget cuts in US federal STEM education funding have been identified for the fiscal year 2018, with far reaching implications. In Australia, the trend is particularly disturbing for girls, where the proportion opting out of mathematics from Year 10 has tripled from 7.5% in 2001 to a staggering 21.4% in 2011. The practical upshot is less students are taking STEM subjects at university, magnifying a future skill shortage in the workforce. 
Bringing it together: Science, Technology, Engineering and Mathematics 
Based on the current trajectory we are burdening future generations with a markedly reduced skill-set. We need to provide students with a more balanced education today. A STEM-literate population is critical for supporting future economic growth and finding solutions to the big issues of tomorrow; one that is sufficiently flexible to meet future needs and can meaningfully debate issues to make informed judgements. This is not just about knowing a random number of scientific ‘facts’, it’s about society understanding how science works: to test ideas and reach the simplest explanation. We desperately need more STEM-literate students across all levels of education, today. Urgent, practical measures are needed. Cutting education programs set up to improve STEM engagement is not the way to do it. But we all have a role to play. We need to value science more in society.
The question is, how do you engage without making it boring? In a little remarked May 2017 report from the Commonwealth Parliament called ‘Innovation and Creativity’, a cross-party committee on Employment, Education and Training has made some far-reaching recommendations to make Australia a more scientifically-literate society. The recommendations range from welcome proposals for dedicated STEM-trained primary school teachers, increased support for the Science in Australia Gender Equity (SAGE) program and expanded provision for STEM-training in tertiary education institutions. A substantial part of this report also focusses on how government and institutions can more meaningfully engage with students.
As a scientist, I fear we have sleep walked into our current predicament. Science has become so specialized; the language is often only understandable to those in the immediate field of endeavor. So much so, it is easy to be perceived as lacking relevance. I don’t believe the public has lost interest, but as a scientist I know we can do better. We have a responsibility to engage the next generation in our work. After twenty years of teaching and research, I believe we can learn from the tales of early scientists and explorers.
A century ago, the great Antarctic explorer Sir Ernest Shackleton remarked: ‘Sentiment has been the ruling force in every great work that has ever been done, and I shall be sorry when the day comes when science is divorced from sentiment or sentiment from science.’ Shackleton realized that science on its own was not enough. You have to excite the public and the best way to do this is by telling stories. And Shackleton was a master. A naval officer by training, Shackleton led the extraordinary Imperial Trans-Antarctic Expedition of 1914–1917. Attempting to cross the unknown Antarctic continent, Shackleton’s ship, the Endurance, was lost to the crushing pressure of pack ice. Shackleton and his men were stuck in the ice for two years. A thousand miles from civilization, they faced isolation, starvation, freezing temperatures, gangrene, wandering icebergs, and the threat of cannibalism. But by sheer positive attitude and superb leadership, the Anglo-Irishman kept his team together, continuing the scientific program even during some of the greatest moments of peril. The safe return of all his men after encountering the perils of the ice was his crowning achievement in the polar regions.
The public were electrified by Shackleton’s tales of adventure and discoveries. Photographs, film, audio recordings, books, newspaper and magazine articles, and public lectures were all used to whisk the audience away to Antarctica. When Shackleton was in a violent storm, you were clinging on to the ship’s tiller with him, when Shackleton was on the edge of starvation, your own stomach gnawed, and when Shackleton laughed at the peculiar idiosyncrasies of the penguins, you were laughing too; all from the safe confines of home. He was so good that other explorers were advised to try to emulate him—though few ever succeeded. Most important of all, Shackleton’s stories provided the public with real insights into the climate, wildlife and geology of the south. Even the most cynical of onlookers were educated about our planet. After Shackleton, Antarctic was no longer an unknown region to the public: it was suddenly real. This was science communication at its best and it set the standard for future efforts.

We need to remember how Shackleton told stories and captured people’s imagination. Scientists need to engage the public with stories — just like Shackleton.

How Antarctic ice melt can be a tipping point for the who...

How Antarctic ice melt can be a tipping point for the whole planet's climate Melting Antarctic ice can trigger effects on the other side of the globe. NASA/Jane Peterson Chris Turney, UNSW ; Jonathan Palmer, UNSW ; Peter Kershaw, Monash University ; Steven Phipps, University of Tasmania , and Zoë Thomas, UNSW

Melting of Antarctica’s ice can trigger rapid warming on the other side of the planet, according to our new research which details how just such an abrupt climate event happened 30,000 years ago, in which the North Atlantic region warmed dramatically.

This idea of “tipping points” in Earth’s system has had something of a bad rap ever since the 2004 blockbuster The Day After Tomorrow purportedly showed how melting polar ice can trigger all manner of global changes.

But while the movie certainly exaggerated the speed and severity of abrupt climate change, we do know that many natural systems are vulnerable to being pushed into different modes of operation. The melting of Greenland’s ice sheet, the retreat of Arctic summer sea ice, and the collapse of the global ocean circulation are all examples of potential vulnerability in a future, warmer world.

Read more: Chasing ice: how ice cores shape our understanding of ancient climate.

Of course it is notoriously hard to predict when and where elements of Earth’s system will abruptly tip into a different state. A key limitation is that historical climate records are often too short to test the skill of our computer models used to predict future environmental change, hampering our ability to plan for potential abrupt changes.

Fortunately, however, nature preserves a wealth of evidence in the landscape that allows us to understand how longer time-scale shifts can happen.

Core values

One of the most important sources of information on past climate tipping points are the kilometre-long cores of ice drilled from the Greenland and Antarctic ice sheets, which preserve exquisitely detailed information stretching back up to 800,000 years.

The Greenland ice cores record massive, millennial-scale swings in temperature that have occurred across the North Atlantic region over the past 90,000 years. The scale of these swings is staggering: in some cases temperatures rose by 16℃ in just a few decades or even years.

Twenty-five of these major so-called Dansgaard–Oeschger (D-O) warming events have been identified. These abrupt swings in temperature happened too quickly to have been caused by Earth’s slowly changing orbit around the Sun. Fascinatingly, when ice cores from Antarctica are compared with those from Greenland, we see a “seesaw” relationship: when it warms in the north, the south cools, and vice versa.

Attempts to explain the cause of this bipolar seesaw have traditionally focused on the North Atlantic region, and include melting ice sheets, changes in ocean circulation or wind patterns.

But as our new research shows, these might not be the only cause of D-O events.

Our new paper, published today in Nature Communications, suggests that another mechanism, with its origins in Antarctica, has also contributed to these rapid seesaws in global temperature.

Tree of knowledge The 30,000-year-old key to climate secrets. Chris Turney, Author provided

We know that there have been major collapses of the Antarctic ice sheet in the past, raising the possibility that these may have tipped one or more parts of the Earth system into a different state. To investigate this idea, we analysed an ancient New Zealand kauri tree that was extracted from a peat swamp near Dargaville, Northland, and which lived between 29,000 and 31,000 years ago.

Through accurate dating, we know that this tree lived through a short D-O event, during which (as explained above) temperatures in the Northern Hemisphere would have risen. Importantly, the unique pattern of atmospheric radioactive carbon (or carbon-14) found in the tree rings allowed us to identify similar changes preserved in climate records from ocean and ice cores (the latter using beryllium-10, an isotope formed by similar processes to carbon-14). This tree thus allows us to compare directly what the climate was doing during a D-O event beyond the polar regions, providing a global picture.

The extraordinary thing we discovered is that the warm D-O event coincided with a 400-year period of surface cooling in the south and a major retreat of Antarctic ice.

When we searched through other climate records for more information about what was happening at the time, we found no evidence of a change in ocean circulation. Instead we found a collapse in the rain-bearing Pacific trade winds over tropical northeast Australia that was coincident with the 400-year southern cooling.

Read more: Two centuries of continuous volcanic eruption may have triggered the end of the ice age.

To explore how melting Antarctic ice might cause such dramatic change in the global climate, we used a climate model to simulate the release of large volumes of freshwater into the Southern Ocean. The model simulations all showed the same response, in agreement with our climate reconstructions: regardless of the amount of freshwater released into the Southern Ocean, the surface waters of the tropical Pacific nevertheless warmed, causing changes to wind patterns that in turn triggered the North Atlantic to warm too.

Future work is now focusing on what caused the Antarctic ice sheets to retreat so dramatically. Regardless of how it happened, it looks like melting ice in the south can drive abrupt global change, something of which we should be aware in a future warmer world.

Chris Turney, Professor of Earth Sciences and Climate Change, UNSW; Jonathan Palmer, Research Fellow, School of Biological, Earth and Environmental Sciences., UNSW; Peter Kershaw, Emeritus Professor, Earth, Atmosphere and Environment, Monash University; Steven Phipps, Palaeo Ice Sheet Modeller, University of Tasmania, and Zoë Thomas, Research Associate, UNSW

This article was originally published on The Conversation. Read the original article.

The Tropics and the Furious Fifties

There’s an old sailor’s expression: “Below 40 degrees south there is no law, below 50 degrees south there is no God.” Since the sixteenth century, sailors have spoken in awe of the violent westerly winds and seas they experienced fighting their way across the Southern Ocean. With few landmasses to slow them down, the winds found across 40 degrees latitude often reach speeds of twenty-five knots—about 40 percent stronger than their northern hemisphere counterparts—earning them the title the “roaring forties.” As shipping pushed farther south, explorers realized that these winds form part of a vast storm belt that includes the “furious fifties” and “screaming sixties,” names more reminiscent of terrible rock bands than a major part of our planet’s circulation system. The early hunters and traders didn’t understand it at the time, but these winds are created by a procession of low-pressure systems carried east by the jet stream, a river of cold air hurtling and twisting round the Antarctic at 10,000 metres. Importantly, something quite profound appears to have been happening in recent decades: The winds seem to be getting even stronger and moving south.

Trying to get a handle on what’s happening in the Southern Ocean, however, is easier said than done. Because the region is notoriously wild, it’s sparse in scientific data. Most of the records we have today come from satellite observations and sporadic records taken by ships as they hastily beat a path to safer latitudes. Fortunately, scattered across the Southern Ocean are a number of tiny pinpricks of land, the so-called subantarctic islands, many of which are home to weather stations that have been taking careful observations since the mid-twentieth century. In the southwest Pacific, the New Zealand subantarctics straddle 48 to 53 degrees south, and lying right under the path of the winds are precious sanctuaries for wildlife, many of whom are suffering a major decline in numbers in recent decades, such as the elephant seals (seen here) and the Rockhopper penguins. Covered in vegetation these islands offer the possibility of finding centuries-old plant and animal remains that preserve a record of the changing impact of the roaring forties and furious fifties.

Elephant seal on the subantarctic islands
On the Australasian Antarctic Expedition 2013-2014, we undertook extensive work on the New Zealand subantarctic islands, with a particular focus on the Auckland and Campbell islands. These islands are home to patches of small native trees called Dracophyllum, a shrub that can grow up to 5 metres high. Their importance for understanding the changing weather is thanks to the genius of Leonardo da Vinci. In the fifteenth century, the Italian polymath realized there was a link between the thickness of tree rings and the growing conditions. Thick rings, he reasoned, must have been when it was a good season for tree growth; narrow rings, terrible. Although we have more sophisticated methods than those available to da Vinci, the principle is still the same. By measuring the ring thickness, we can get a handle on changing climate. Dracophyllum is one of nature’s weather stations, putting down a ring of growth each year.

In a paper recently published in the journal Climate of the Past called ‘Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction’, we report the changes recorded by the Dracophyllum trees and compare these to climate models. The trees are truly a remarkable natural weather station, more than doubling the length of the observational record kept carefully by scientists working on the islands. But the big discovery is that since the mid-twentieth century, the trees reveal the climate in the southwest Pacific has become increasingly more extreme, apparently caused by changing winds in the Furious Fifties. Sometimes the wind has weakened, allowing warm airmasses to pass over the islands; at other times, the westerly winds have roared, bringing cold southerly blasts.

When we drilled down further into what was happening, we found the pattern of alternating warm and cold winds matched the climate changes seen in the tropical Pacific, a phenomenon known as the El Niño-Southern Oscillation. ENSO, as its commonly abbreviated, describes changes in tropical ocean temperatures every 2 to 8 years that can have a major effect on the global atmospheric circulation system. The remarkable thing is as tropical Pacific Ocean waters have warmed from the mid-twentieth century, the global climate system seems to be changing too. And nowhere is this more apparent than over the New Zealand subantarctic islands. And as the climate swings from one extreme to another it looks like these changes might be hammering the mammal and sea bird populations that call this part of the world home. Why is the big question? One possibility is the increasingly variable climate is impacting food sources in the region; something we’re hoping to test in future work.

You can download our paper ‘Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction’ from Climate of the Past for free at http://www.clim-past.net/13/231/2017/. Hope you enjoy it.

Echoes of an ancient time in Australia

Exciting results published today in the international science journal Nature provide precious new insights into the arrival and movement of humans across Australia over a staggering 50,000 years. 
Sadly, many Aboriginal Australians no longer live where their ancestors had called home. So to better understand Australia’s history before the arrival of Europeans, a forward-thinking initiative called the Aboriginal Heritage Project was set up. Led by the University of Adelaide’s Australian Centre for Ancient DNA (ACAD) in partnership with the South Australian Museum and Aboriginal families and communities, the team – in which I was fortunate to play a small part – have uncovered some remarkable new findings. 
Headed by Alan Cooper and Ray Tobler, the ACAD group analysed over 100 hair samples collected with consent from Aboriginal people across the continent between the 1920s and 1970s. These samples were collected as part of a project where along with hair, detailed records of the individual, their family and culural heritage were documented by University of Adelaide researchers. 
The hair samples are truly precious, preserving mitochondrial DNA that is inherited through the mother back to the very founding Aboriginal population of Australia. The wonderful thing is the samples allow us to reconstruct a map of Aboriginal Australia before the arrival of Europeans. Crucially, over tens of thousands of years, the genetic code accumulates mutations at a fairly steady rate. This ‘molecular clock’ allows us to date the timing of arrival and migration across the continent. The genetic data revesals a story consistent with published archaeological evidence for human arrival some 50,000 years but give new insights into how the continent was settled over an almost unimaginable length of time.
The peopling of Australia. Genetic groups given by letters.
Ages shown as thousands of years ago (ka). Source: Tobler et al., Nature. 
The new results seem to show that the early population rapidly moved around the eastern and western fringes of Australia. Within just a couple of thousand years they had moved quickly enough  to meet on the other side of the country somewhere near the Eyre Peninsula, South Australia.  But the headline result is that in spite of all the climate and environmental extremes that followed, communities don’t appear to have moved much after this. Genetic differences are found in groups from specific geographic regions and don’t seem to have mixed much at all. Not when the mega-arid ice age occurred 20,000 years ago. Or when sea levels rose dramatically 14,000 years ago. Instead of mass migration, the data suggests communities may have only moved within the immediate region. The basic pattern of effectively held for 50,000 years. No wonder Aborigine communities speak so movingly of their links to country.
A central pillar of the Aboriginal Heritage Project is that Aboriginal families and communities have been closely involved with the project from its inception and that analyses are only conducted with their consent. Importantly, results are first discussed with the families to get Aboriginal perspectives before scientific publication. The research model was developed under the guidance of Aboriginal elders, the Genographic Project, and professional ethicists. This is the first phase of a decade-long project that will allow people with Aboriginal heritage to trace their regional ancestry and reconstruct family genealogical history, and will also assist with the repatriation of Aboriginal artefacts.
“Aboriginal people have always known that we have been on our land since the start of our time,” says Kaurna Elder Mr Lewis O’Brien, who is one of the original hair donors and has been on the advisory group for the study. “But it is important to have science show that to the rest of the world. This is an exciting project and we hope it will help assist those of our people from the Stolen Generation and others to reunite with their families.”
A video on the project and findings can be seen at https://youtu.be/R6LzbKszKhQ
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The research article led by Alan Cooper and Ray Tobler is called ‘Aboriginal mitogenomes reveal 50,000 years of regionalism in Australia’ and published today in Nature . There's also a lovely piece by the team in The Conversation at http://theconversation.com/dna-reveals-aboriginal-people-had-a-long-and-settled-connection-to-country-73958. 

The Day After Tomorrow

New research suggests something like the movie The Day After Tomorrow may have happened in the past, with sobering implications for the future. In this blockbuster, melting Arctic ice led to dramatic cooling across the Northern Hemisphere, highlighting the paradox that in a warming world, some regions may indeed cool (or at least not warm as much as expected). Whilst no one is suggesting this could lead to a new ice age, climate model projections do suggest some parts of the world may respond differently to long-term warming. One of the big uncertainties is the impact a melting Greenland ice sheet might have across the North Atlantic. At a simple level, the world’s oceans are connected as though by one enormous conveyor belt. At one end of the loop, warm tropical waters popularly known as the Gulf Stream drift up into the North Atlantic where over the course of a year the evaporating surface delivers heat downwind equivalent to the output from a million power stations. It’s a major reason for the starkly different temperatures experienced along the northern 50th parallel; why Europe is over 15˚C warmer than Newfoundland and Labrador on the other side of the Atlantic. Eventually, however, this northward-flowing current becomes too cold and salty to stay afloat, and sinks, heading south kilometres below the surface. If enough of Greenland warms, the fresh water released by a melting ice sheet may be sufficient to dilute the surface ocean waters and stop the formation of salty, dense water, breaking the loop. One way to resolve future uncertainty is to look into the past when conditions were warmer than today. Regular Intrepid Science followers will have read previous work we’ve done on the Last Interglacial but the short story is this was a period around 127,000 to 116,000 years ago when polar regions were some 2˚C warmer than present day - a potential scenario for the future [thanks to long-term changes in the Earth’s orbit, our planet received extra warmth from the Sun, triggering a host of changes that include less Arctic sea ice and carbon release from the oceans and permafrost, amplifying warming. These so-called ‘positive feedbacks’ are a real concern for future climate change but that’s another story]. 
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Where the Greenland Ice Sheet meets the North Atlantic. Icebergs in high summer in Sermilik Fjord, one of the largest fjords in southeast greenland. Helheim glacier, which drains into the fjord, has seen some of the highest acceleration of ice velocity recorded across the Greenland Ice sheet over the past decade (credit: C.J. Fogwill).
By looking at the recent geologic record we can reconstruct what happened in the North Atlantic during the Last Interglacial. A few years ago, a great mate, Richard Jones, and I produced the first global temperature reconstruction for the Last Interglacial (published in Journal of Quaternary Science as ‘Does the Agulhas Current amplify global temperatures during super-interglacials?’). With an international team of friends from the universities of Exeter, UNSW, Lund and the Natural History Museum (London), we’ve now published a new study in the journal Geology called ‘Delayed maximum northern European summer temperatures during the Last Interglacial as a result of Greenland Ice Sheet melt’. Drilling some 5 metres of Last Interglacial lake muds in Denmark we’ve been able to extract fossil remains of what are known as non-biting midges (something referred to as ‘chironomids’). Chironomids are wonderful for reconstructing past climate. The surface lake water temperatures they inhabit dictate what species can exist at any one time. Some species thrive in warm waters, others prefer more frigid conditions. The practical upshot is by extracting the minute remains of chironomids preserved in the lake muds layer-by-layer, it’s possible to reconstruct how temperatures have changed over time. To our amazement we found the warmest temperatures didn’t happen at the start of the Last Interglacial but some 3000 years later. And when we compared our reconstruction to ocean and ice core records across the North Atlantic, we reached a startling conclusion. The summer temperatures mapped onto what was happening with the Greenland ice sheet: when Greenland was melting, summer temperatures effectively downstream over Europe were relatively cool. And when the Greenland ice sheet stopped melting, Europe warmed dramatically. Worryingly, recent work by Stefan Rahmstorf at the Potsdam Institute for Climate Impact Research and colleagues suggest this may already be happening. 
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Ice cold in Commonwealth Bay

Commonwealth Bay in the East Antarctic will be forever associated with Sir Douglas Mawson’s pioneering scientific venture a century ago: the Australasian Antarctic Expedition. Mawson’s team had only intended to spend one year south, but it was not to be. A sudden turn of events led to tragedy on the ice, the deaths of two men, allegations of cannibalism and, with the return of winter sea ice, an extended stay in Antarctica. While the efforts of Mawson and his men laid the foundations for modern Antarctic science, the region has continued to experience dramatic change. And it doesn’t get any more dramatic than the arrival of iceberg B09B in 2011. The word ‘berg’ doesn’t really do it justice though – B09B is a monster. Weighing in at an estimated 500 billion tonnes, this block of ice is 97 miles long and over 20 kilometres wide. There’s enough freshwater in B09B to provide all of New York’s drinking needs for 300 years. And it started out even larger. In 1987, an iceberg the size of Bali broke free from the continent in the Ross Sea. It was one of the largest bergs ever seen. Riding the westward-flowing ocean currents, the Ross Sea berg smashed its way along the coast. By the time it reached Commonwealth Bay, the largest remaining part was labelled with the unassuming moniker B09B. Smashing a tongue of ice from the Mertz Glacier that extended 100 kilometres out to sea, the berg ground itself in Commonwealth Bay, trapping a vast amount of sea ice.
Icebergs in Commonwealth Bay
Normally, chilling Antarctic winds blow off the continent year round, freezing the surface of Commonwealth Bay, regardless of whether it’s winter or not: the sea ice is formed, blown offshore, a new open area of water known as a polynya is formed, and more seawater is frozen in its place.  As sea ice is created offshore, a fundamental process takes place below the surface. The salt in ocean water is effectively squeezed out of the ice creating a dense mass of water. In most of the Southern Ocean, this cold, super-salty water just diffuses away. In Commonwealth Bay, however, the conditions are perfect for the formation of something known as Antarctic Bottom Water, a super cold water mass that forms a key part of the world’s ocean circulation system. Worryingly, some scientists have suggested the arrival of B09B may have completely stalled Antarctic Bottom Water production, with potentially global implications.
As part of the Australasian Antarctic Expedition 2013-2014 we wanted to find out just what impact the arrival of B09B has had on ocean circulation. Ably led by Chris Fogwill and Erik van Sebille, we have a new paper out in The Cryosphere journal: ‘Impacts of a developing polynya off Commonwealth Bay, East Antarctica, triggered by grounding of iceberg B09B’. Here we report temperature and salinity across the area and compare these to previous measurements – including those made by Mawson and his team – and some very exciting ocean modelling results headed up by Eva Cougnon. The headline discovery is the polynya appears to have moved out into Commonwealth Bay, and may have led to resumption of Antarctic Bottom Water formation, in part compensating for the reduction around the Mertz Glacier. This is a fascinating find. Further work is now needed to continue monitoring this sensitive region of our planet to see whether the recovery continues into the future.

You can read our research paper for free at http://www.the-cryosphere.net/10/2603/2016/.

Giving future Australian drought a 500-year perspective

Here at Intrepid Science we focus a lot of effort on trying to better reconstruct past climate and environmental change. The main reason is that by understanding what happened when in the recent geologic record we can reduce the uncertainties surrounding future climate change and its impact(s). But don’t be misled by the term ‘geologic record’. Basically we’re looking beyond the historic record of scientific observations by reading what’s preserved in the landscape – what are sometimes described as ‘natural archives’. Nature has a fabulously diverse library and can include trees, corals and even ice cores. The real test is finding these ‘books’. As a result, the team work around the world unearthing new records.

One of our most recent projects is to reconstruct changing drought across eastern Australia and New Zealand over the last 500 years. When Australia experiences a drought, it can cause billions of dollars of environmental and economic damage. A classic example is the ‘Millennium Drought’ of the late 1990s-2009 when the shortage of rain caused fires across southeastern Australia that included the ‘Black Saturday’ fires that tragically claimed 173 lives and cost an estimated US$3 billion. Climate doesn’t get much more extreme than in Australia. By using tree ring records of growing conditions – which are strongly influenced by the amount of moisture available for growth – and corals that preserve a record of river flow off the Queensland interior, we have developed an atlas of drought: a year-by-year map of wet-dry conditions resolved at 0.5˚ latitude by 0.5˚ longitude. We previously reported the drought atlas at the end of last year (you can download the original paper for free at http://iopscience.iop.org/article/10.1088/1748-9326/10/12/124002. If you’re interested, the 500 years has been compressed into a 2 minute movie at https://www.youtube.com/watch?v=9w-xzhQoyUY).

Australian trees preserve a year-by-year record of drought
Now, the brilliant Ben Cook at +NASA and a fantastic team has interrogated the atlas and compared how past droughts compare to climate projections for the twenty-first century. The paper is called ‘The paleoclimate context and future trajectory of extreme summer hydroclimate in eastern Australia’ and can be found at http://onlinelibrary.wiley.com/doi/10.1002/2016JD024892/abstract. For the period of overlap, the models do a good job capturing our reconstructed droughts. Looking forward there’s a worrying trend: average conditions in eastern Australia are expected to become drier during the latter half of the 21st century, with a greater risk of extremes similar to the Millennium Drought. Multi-year droughts look like they will become increasingly common in the future as a result of both natural variations and anthropogenic forcing. A major implication is we need to future proof Australia as much as possible against the increasing likelihood of similar events occurring over the next century.

This work was funded by the Australian Research Council (ARC) and we gratefully acknowledge their support.