We have exciting news!!!  Our Synergia project will be funded by the Swiss National Science Foundation!

This project will help scientists to better understand the impacts of large volcanic eruptions on the Climate System and their effects on human societies. The project hasn’t started yet but If you want to know more about our research questions, feel free to read the abstract below:

CALDERA – EffeCts of lArge voLcanic eruptions on climate and societies: UnDerstand the impacts of past Events and related subsidence cRises to evAluate potential risks in the future

Large explosive volcanic eruptions can inject massive amounts of sulphuric gases into the stratosphere. Sulphate aerosols – produced in the stratosphere by the oxidation of these gases (mainly SO2 and H2S) – can sub-stantially perturb Earth’s radiative balance and lead to a cooling of the troposphere and surface temperatures at timescales of months to years. Volcanically induced cooling was held responsible for crop failures and the subsequent rise in grain prices, and to thereby contribute to subsistence crisis and famines. The explosive erup-tion of Tambora in April 1815 – the largest event of the last 500 years – yielded strong evidence for a causal links between extreme weather experienced in 1816 in parts of the northern hemisphere (year without summer), poor harvests, a sharp rise in grain prices in Europe and America and the last great subsistence crisis of the Western world. It is often assumed that such consequences are unlikely to occur in modern societies as globalized food trade networks and disaster relief can offer a collective response to modern crises. Yet, one only needs to consider the catalogue of recent famines that have afflicted many parts of Africa, and the slow and often ineffective international response, to find ample evidence that modern societies are in no way immune to potentially catastrophic impacts of major volcanic eruptions. As no “Tambora-scale” eruption has occurred during the 20th century, we lack experience of potential impacts of high-magnitude eruptions on modern societies. This lack of knowledge –in terms of spatio-temporal climatic impacts and societal abilities to respond to such disasters – calls for in-depth transdisciplinary research.

The key aim of the CALDERA project is to document and reconstruct the spatio-temporal impacts of past major eruptions in unprecedented detail with proxy records and climate models. It also aims at providing state-of-the-art climate projections (i) to quantify impacts of future eruption scenarios on crop yield and global food security (ii) and to assess whether future, major eruptions could mitigate global warming, or instead generate persistent climate instability. CALDERA will thus substantially improve our knowledge of the impacts of volcanism on temperature and precipitation anomalies by employing (a) recently unearthed historical archives, (b) unprecedented, millennia-long tree-ring datasets (spanning 7000 yrs) of wood-anatomic parameters (c) in combination with a tailored processing of PAGES 2k global datasets. This benchmark data will be used to (d) calibrate microphysical/climate models to more realistically simulate the cooling and hydroclimatic anomalies induced by those 28 eruptions of the last 2000 years being at least as big as the Pinatubo event in 1991. In addition, the project will (e) determine the role of volcanism in the transition from Medieval Climate Anomaly to Little Ice Age climatic regimes, and (f) examine societal impacts and responses to volcanically induced climatic anomalies in these periods using historical archives. The calibrated climate model predictions will then be (g) employed to simulate a suite of future “Tambora-scale” scenarios to provide the climatic input data for statistical crop yield models and to document the effect of volcanic activity on agricultural production, (h) its likely impacts on global food systems and trade, as well as on (i) water and energy (in line with the water-energy-food nexus). The key strength of CALDERA lies in the systematic, transdisciplinary coupling of approaches and generation of unique, high-resolution datasets to better understand the effects of past, massive volcanism, but also to comprehend and forecast environmental and socio-economic impacts of future volcanic disasters. In addition, the synergetic efforts of the CALDERA consortium will generate breakthrough outcomes which could not be reached by individual teams and within separate disciplines.

L’article CALDERA – EffeCts of lArge voLcanic eruptions on climate and societies: UnDerstand the impacts of past Events and related subsidence cRises to evAluate potential risks in the future est apparu en premier sur Dendrolab.

We have good news!! We have just received the confirmation that the Swiss National Science Foundation will fund our TURBERAS project. If you want to know more about this exciting project feel free to read the abstract below:

TURBERAS: Reconstruction of Holocene hydro-climatic fluctuations based on multi-proxy peatland records

The anticipated impact of ongoing and projected future climate changes on ecosystems and societies is a crucial concern that requires detailed understanding of the climate system in general, but also natural climate variability and its forcing mechanisms in particular. A suite of paleoclimate reconstructions has advanced our understanding of climate dynamics over much of the Holocene, mostly in terms of temperature variations. By contrast, it is quite striking to see how little we still know about past hydro-climatic changes, mostly because of a persistent scarcity of annually resolved proxies that has so far prevented an extension or densification of annually resolved, hydro-climatic reconstructions across major parts of the Holocene.

Subfossil trees from peatlands of Northern Europe and Scandinavia have been shown to be sensitive to changes in hydro-climatic variability. Paradoxically, however, the resulting tree-ring series could not be used so far to quantify the amplitude of moisture changes at the annual scale. This was due to the fact that peatland trees, in contrast to trees growing on mineral soils, show more complex, often weaker, and clearly site-dependent responses to monthly temperature and precipitation changes, with the latter presumably reflecting a multi-annual synthesis of moisture variability and water-table changes related to a hydrological lag in peatlands. Here we hypothesize that our current understanding of past hydro-climatic variability would benefit quite substantially from a systematic coupling of different, peat-based proxies – such as testate amoebae, diatoms, pollen, non-pollinic microfossils, tree rings – with different temporal resolutions.

Based on the above considerations, the TURBERAS project has four key objectives that will be addressed in two case study regions in Estonia and Sweden: (i) augment the pool of existing, moisture-sensitive peatland tree-ring width series in the case-study region; (ii) understand and quantify hydrological lag effects recorded in tree growth following changes in precipitation and water-table fluctuations using automated dendrometers, cell-wall thickness and isotope measurements; (iii) develop transfer functions between the tree-growth parameters identified under point (ii) and climate variables by taking account of hydrological lags; (iv) based on point (iii), reconstruct climate using a multi-proxy approach in which other, existing peatland proxies (i.e. testate amoebae, diatoms, pollen, non-pollinic microfossils,) are used to add the middle and low frequency signals to the annually-resolved tree-ring records. The key innovation of the project in terms of long-term hydro-climatic reconstructions lies in the diversification of tree proxies (tree-ring width, cell wall thickness, isotopes) and their systematic coupling with water-table-sensitive proxies such as plant macrofossil assemblages, testate amoebae and diatoms existing at the two case-study regions, but for the latter mostly with lower temporal resolutions. The proposed procedure uses three analytical steps: (a) a spectral algorithm with a Fast Fourier Transformation to decompose both the different proxy records and climatic matrixes into their low and high frequency components. After decomposition, (b) using the proxy matrix for each frequency component to reconstruct the corresponding band of climatic data over the Holocene. Finally, (c) assembling the two bands in one single band and back-transformation of results into original meteorological data using an inverse modeling procedure.

The TURBERAS project is designed in a way that should allow key insights into how woody vegetation in fragile wetland ecosystems evolves over time and into how tree growth is controlled by hydro-climatic fluctuations. In return, we also expect to provide reconstructions of past hydro-climatic changes for key periods of the Holocene.

L’article TURBERAS: Reconstruction of Holocene hydro-climatic fluctuations based on multi-proxy peatland records est apparu en premier sur Dendrolab.

January 2018 was a month of extremes. Not only was it by far the warmest January on record across the Western Alps, but also one of the wettest in systematic weather measurements, with widespread landslides at low elevations and massive snowfall in mountains.

The weather of January 2018 was unusual, freakish in fact, at the upper extreme of the historical distribution of storminess, temperatures and precipitation in the Western Alps – breaking many weather records. Not only was January 2018 unprecedentedly warm, but also was it extremely wet and with unusual snowfall at higher elevations. As Regional Climate Models do not only predict substantial warming in the European Alps but also a slight increase in precipitation totals, we hypothesize that the extreme weather conditions observed during January 2018 and its ensuing impacts could yield valuable insights into typical winter conditions to be expected by the end of the 21^st century.

At higher elevations, the January 2018 calamities started with the passage of winter storm Burglind (Eleanor) and new all-time wind gust records on summits as well as hefty snowfall in the Northern French and Western Swiss Alps. During the first three weeks of January, subsequent, stormy low-pressure systems transported further warm-wet air masses from the Atlantic and the Mediterranean to the Alps, leaving snow accumulations exceeding five meters (and even eight meters in regions affected by massive snowdrift, like Grand St. Bernard; Fig. 1b). These immense snow burdens pushed avalanche risk to extreme levels in the Alps, threatening many villages and communication routes, and leaving thousands of tourists stranded in mountain resorts. Indeed, several of the major ski destinations of the Alps, including Chamonix, Saas Fee, Val d’Isère, or Zermatt, had to shut their ski runs and to put helicopter shuttles in place to evacuate tourists from resorts during the major snowfall episodes.

Local residents and authorities were, however, not equally well prepared for the widespread, shallow landsliding, debris flows and rain-on-snow floods in smaller, low-elevation catchments in January 2018. This can at least in part be credited to a lack of experience with comparable events during other winter seasons, for which there is virtually no historical evidence of rainfall-induced mass movements, despite scientific surmise that ongoing climate warming could indeed promote landslides and debris flows, even at higher elevations and in winter.

For further information, read the paper entitled Future winters glimpsed in the Alps.

L’article January 2018 : Living through a future winter est apparu en premier sur Dendrolab.

Often called the Third Pole, the Hindukush-Karakoram-Himalaya region, comprising the Tibetan plateau and the surrounding mountains, is the most glaciated place on Earth outside the North and South Poles. Its cryosphere is extremely susceptible—and the surrounding communities and ecosystems vulnerable—to the effects of climate change. Juan Ballesteros-Cánovas and colleagues at the University of Geneva have used tree-ring data to reconstruct more than 150 years of snow avalanches on a typical western Himalayan mountainside in northern India. Tree rings record damage, evidence of tilting, and abrupt changes in growth rate. As a result, they provide a spatially and temporally accurate history of avalanche events. Samples from 144 trees revealed more than 500 avalanche-related tree-growth anomalies that documented 38 years with snow avalanches since 1855. The researchers found substantial increases in both frequency and affected area since the 1970s.

To investigate possible linkages between climate change and the increased avalanche incidence, the team employed an innovative model that incorporated the effect that one avalanche can have on the likelihood of future ones. Of the principal variables characterizing the local climate, the researchers found only one significant contributor to avalanche frequency—increased air temperature between December and March. That connection is corroborated by direct observations in the surrounding regions: Many recent avalanches occurred in late winter or early spring and involved wet snow, which has a higher shear-deformation rate than dry snow. The increased likelihood, heavier snow, and further down-slope extent greatly exacerbate the avalanche risk to communities and infrastructure in the western Himalayas, the researchers note.

For further information, please read our paper written in the Proceedings of the National Academy of Sciences and entitled : Climate warming enhances snow avalanche risk in the Western Himalayas.

You may also read this very nice article published in Wired  Deep inside the deadly avalanche that climate change built.

L’article Warming increases risk of snow avalanches in the western Himalayas est apparu en premier sur Dendrolab.

 

Memories of the largest lava flood in the history of Iceland, recorded in an apocalyptic medieval poem, were used to drive the island’s conversion to Christianity, new research suggests.

A team of scientists and medieval historians, led by the University of Cambridge, has used information contained within ice cores and tree rings to accurately date a massive volcanic eruption, which took place soon after the island was first settled.

Having dated the eruption, the researchers found that Iceland’s most celebrated medieval poem, which describes the end of the pagan gods and the coming of a new, singular god, describes the eruption and uses memories of it to stimulate the Christianisation of Iceland. The results are reported in the journal Climatic Change.

The eruption of the Eldgjá in the tenth century is known as a lava flood: a rare type of prolonged volcanic eruption in which huge flows of lava engulf the landscape, accompanied by a haze of sulphurous gases. Iceland specialises in this type of eruption — the last example occurred in 2015, and it affected air quality 1400 kilometres away in Ireland.

The Eldgjá lava flood affected southern Iceland within a century of the island’s settlement by Vikings and Celts around 874, but until now the date of the eruption has been uncertain, hindering investigation of its likely impacts. It was a colossal event with around 20 cubic kilometres of lava erupted — enough to cover all of England up to the ankles.

The Cambridge-led team pinpointed the date of the eruption using ice core records from Greenland that preserve the volcanic fallout from Eldgjá. Using the clues contained within the ice cores, the researchers found that the eruption began around the spring of 939 and continued at least through the autumn of 940.

“This places the eruption squarely within the experience of the first two or three generations of Iceland’s settlers,” said first author Dr Clive Oppenheimer of Cambridge’s Department of Geography. “Some of the first wave of migrants to Iceland, brought over as children, may well have witnessed the eruption.”

Once they had a date for the Eldgjá eruption, the team then investigated its consequences. First, a haze of sulphurous dust spread across Europe, recorded as sightings of an exceptionally blood-red and weakened Sun in Irish, German and Italian chronicles from the same period.

Then the climate cooled as the dust layer reduced the amount of sunlight reaching the surface, which is evident from tree rings from across the Northern Hemisphere. The evidence contained in the tree rings suggests the eruption triggered one of the coolest summers of the last 1500 years. “In 940, summer cooling was most pronounced in Central Europe, Scandinavia, the Canadian Rockies, Alaska and Central Asia, with summer average temperatures 2°C lower,” said co-author Professor Markus Stoffel from the University of Geneva’s Department of Earth Sciences.

The team then looked at medieval chronicles to see how the cooling climate impacted society. “It was a massive eruption, but we were still amazed just how abundant the historical evidence is for the eruption’s consequences,” said co-author Dr Tim Newfield, from Georgetown University’s Departments of History and Biology. “Human suffering in the wake of Eldgjá was widespread. From northern Europe to northern China, people experienced long, hard winters and severe spring-summer drought. Locust infestations and livestock mortalities occurred. Famine did not set in everywhere, but in the early 940s we read of starvation and vast mortality in parts of Germany, Iraq and China.”

“The effects of the Eldgjá eruption must have been devastating for the young colony on Iceland — very likely, land was abandoned and famine severe,” said co-author Professor Andy Orchard from the University of Oxford’s Faculty of English. “However, there are no surviving texts from Iceland itself during this time that provide us with direct accounts of the eruption.”

But Iceland’s most celebrated medieval poem, Voluspá (‘The prophecy of the seeress’) does appear to give an impression of what the eruption was like. The poem, which can be dated as far back as 961, foretells the end of Iceland’s pagan gods and the coming of a new, singular god: in other words, the conversion of Iceland to Christianity, which was formalised around the turn of the eleventh century.

Part of the poem describes a terrible eruption with fiery explosions lighting up the sky, and the Sun obscured by thick clouds of ash and steam:

“The sun starts to turn black, land sinks into sea; the bright stars scatter from the sky. Steam spurts up with what nourishes life, flame flies high against heaven itself.”

The poem also depicts cold summers that would be expected after a massive eruption, and the researchers link these descriptions to the spectacle and impacts of the Eldgjá eruption, the largest in Iceland since its settlement.

The poem’s apocalyptic imagery marks the fiery end to the world of the old gods. The researchers suggest that these lines in the poem may have been intended to rekindle harrowing memories of the eruption to stimulate the massive religious and cultural shift taking place in Iceland in the last decades of the tenth century.

“With a firm date for the eruption, many entries in medieval chronicles snap into place as likely consequences — sightings in Europe of an extraordinary atmospheric haze; severe winters; and cold summers, poor harvests; and food shortages,” said Oppenheimer. “But most striking is the almost eyewitness style in which the eruption is depicted in Voluspá. The poem’s interpretation as a prophecy of the end of the pagan gods and their replacement by the one, singular god, suggests that memories of this terrible volcanic eruption were purposefully provoked to stimulate the Christianisation of Iceland.”

For further information, have a look at our article written in Climatic Change.

L’article A Violent Volcanic Eruption Immortalized in Medieval Poem May Have Spurred Iceland’s Adoption of Christianity est apparu en premier sur Dendrolab.

Ranking among the largest volcanic eruptions of the Common Era (CE), the ‘Millennium Eruption’ of Changbaishan produced a widely-dispersed tephra layer (known as the B-Tm ash), which represents an important tie point for palaeoenvironmental studies in East Asia. Hitherto, there has been no consensus on its age, with estimates spanning at least the tenth century CE. Here, we identify the cosmogenic radiocarbon signal of 775 CE in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption. Combined with glaciochemical evidence from Greenland, this enables us to date the eruption to late 946 CE. This secure date rules out the possibility that the Millennium Eruption contributed to the collapse of the Bohai Kingdom (Manchuria/Korea) in 926 CE, as has previously been hypothesised. Further, despite the magnitude of the eruption, we do not see a consequent cooling signal in tree-ring-based reconstructions of Northern Hemisphere summer temperatures. A tightly-constrained date for the Millennium Eruption improves the prospect for further investigations of historical sources that may shed light on the eruption’s impacts, and enhances the value of the B-Tm ash as a chronostratigraphic marker.

For further information, have a look at our article written in Quaternary Science Reviews.

L’article Multi-proxy dating the ‘Millennium Eruption’ of Changbaishan to late 946 CE est apparu en premier sur Dendrolab.

Volcanology : Chronicling a medieval eruption

 

The eruption of Samalas in Indonesia in 1257 ranks among the largest sulfur-rich eruptions of the Common Era with sulfur deposition in ice cores reaching twice the volume of the Tambora eruption in 1815. Sedimentological analyses of deposits confirm the exceptional size of the event, which had both an eruption magnitude and a volcanic explosivity index of 7. During the Samalas eruption, more than 40 km³ of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km. However, the climatic response to the Samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of Northern Hemisphere summers than inferred from tree-ring-based temperature reconstructions. Here, we draw on historical archives, ice-core data and tree-ring records to reconstruct the spatial and temporal climate response to the Samalas eruption. We find that 1258 and 1259 experienced some of the coldest Northern Hemisphere summers of the past millennium. However, cooling across the Northern Hemisphere was spatially heterogeneous. Western Europe, Siberia and Japan experienced strong cooling, coinciding with warmer-than-average conditions over Alaska and northern Canada. We suggest that in North America, volcanic radiative forcing was modulated by a positive phase of the El Niño–Southern Oscillation. Contemporary records attest to severe famines in England and Japan, but these began prior to the eruption. We conclude that the Samalas eruption aggravated existing crises, but did not trigger the famines.

For further information, you can read our paper entitled Climate response to the Samalas volcanic eruption in 1257 revealed by proxy records.

L’article Volcanology : Chronicling a medieval eruption est apparu en premier sur Dendrolab.