Heinz Wanner - Academia.edu (original) (raw)

Papers by Heinz Wanner

Quaternary Science Reviews, 2016

statistical correlations. Glacier retreat in the past 100e150 years corresponds to the anthropoge... more statistical correlations. Glacier retreat in the past 100e150 years corresponds to the anthropogenic global temperature increase. Many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain.

Environmental Research Letters, 2016

The spatial context is critical when assessing present-day climate anomalies, attributing them to... more The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal timescales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

Quaternary Science Reviews, 2011

The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustain... more The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed and presented in form of a Holocene Climate Atlas (HOCLAT; see http://www.oeschger.unibe.ch/ research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.

Informationen und Beiträge zur Klimaforschung Contributions à la recherche climatologique Luft-un... more Informationen und Beiträge zur Klimaforschung Contributions à la recherche climatologique Luft-und Satellitenbilder als mögliche Datenquellen bei der Schneekartierung Die Lufttrübungserscheinungen des Sommers 1783 in der Sicht schweizerischer Beobachter Untersuchungen über die Nebelhäufigkeit in Bern zwischen 1761 und 1969 Die Klimageschichte-eine vergessene Wissenschaft? / L'histoire du climat-une science oubliée?

Greenland ice core records show that, prior to the 20th century, temperatures during the Holocene... more Greenland ice core records show that, prior to the 20th century, temperatures during the Holocene in the Northern Hemisphere mid and high latitudes were only higher during the so-called “Holocene Climate Optimum”. Pollen analysis has demonstrated that this warmer period, also called “Atlantikum”, occurred in the Canadian Arctic, North Atlantic and Europe between approximately 8000 and 4500 cal yr BP. Glaciological evidence reveals that, during the mid-Holocene, the glaciers strongly retreated in the European Alps, the Canadian Rockies, in the Arctic and other regions of the northern hemisphere. Macrofossils bring evidences that the northern tree line moved north and was located at the Arctic coast over most of Russia. Antarctic ice cores show a widespread Holocene warm period between 11,500 and 9000 cal yr BP and secondary warmer phases in the Ross Sea sector (8000 – 6000 cal yr BP) and eastern Antarctica (6000 – 3000 cal yr BP). There is a lively debate whether the Holocene climate...

werden. Wir verstehen ihn hier als die Zeitperiode, in der sich die Randbedingungen des Klimasyst... more werden. Wir verstehen ihn hier als die Zeitperiode, in der sich die Randbedingungen des Klimasystems nicht mehr dramatisch verandert haben. Abbildung 1 zeigt die Meeresspiegelveranderungen in der sudlichen Nordsee wahrend der letzten 10 000 Jahre, wie sie von Karl-Ernst Behre vom Niedersachsischen Institut fur Kustenforschung ermittelt wurden. Daraus ist ersichtlich, dass die Abschmelzprozesse im Bereich der grosen Eisschilder, vor allem auf den Nordkontinenten Amerika und Eurasien, um zirka 6000 Jahre vor heute zum grosten Teil abgeschlossen waren. Damit haben wir die Gewahr, dass grosere Reorganisationen im Klimasystem, vor allem in Form von Veranderungen der thermohalinen Zirkulation im Ozean, bisher ausgeblieben sind. In diese Phase der letzten 6000 Jahre fallt zudem der starke Wandel mit dem Ubergang von den Jagern und Sammlern zur Sesshaftigkeit und schlieslich zum modernen Gesellschaftssystem. Wir beschranken uns deshalb auf diesen Zeitabschnitt, der neben der historischen au...

Nature Geoscience, 2018

In the version of this Article originally published, the 'Data availability' section contained an... more In the version of this Article originally published, the 'Data availability' section contained an incorrect DOI for data from the FLATS (XV) seismic network (

PAGES news, 2009

Towards a global synthesis of the climate of the last two millennia Workshop of the PAGES 2k Regi... more Towards a global synthesis of the climate of the last two millennia Workshop of the PAGES 2k Regional Network-Corvallis, USA, 7 July 2009 louiSe newman 1 , h. wanneR 2 and t. kieFeR 1

PAGES news, 2002

Before the advent of instrumental records, up to 20 observations a day were carried out at specif... more Before the advent of instrumental records, up to 20 observations a day were carried out at specific sites, by the same observer, following defined rules. Despite this plethora of data, many scientists are of the opinion that observations made before the instrumental period are "subjective" and less reliable than natural proxies. But these data were collected by very experienced scientists and observers. Once calibrated and verified in the present, the data are precise and have a spatiotemporal resolution unmatched by any other climate proxy data. They are probably the best data source for the reconstruction of climatic state parameters in continental areas for the period between 1500 and 1850. In addition, a worldwide data base of daily information is being put together for the worlds major oceanic areas from naval logbooks (project CLIWOC). Natural disasters are a major source of societal concern in the context of climatic change. However, the record of instrumental measurements is too short to explore natural patterns of disasters. This also holds for investigations into societal vulnerability. In this context, documentary evidence is invaluable. This issue of PAGES News mirrors the fact that investigations on documentary data are unevenly distributed on the globe. On one hand, this distribution is related to the abundance and availability of the data sources, which, in China go back for several thousand and in Europe for several hundred years. On the other hand, this kind of research has until recently been somewhat neglected in the Americas, where written sources begin with the European settlement. In Australia and in Africa records are almost absent. Curiously, hardly any research has been devoted to the Islamic world, despite its long standing tradition of keeping annals. Dealing with documentary data requires a historian's skills. Scientists tend to overlook the pitfalls inherent in this data and are usually not familiar with old languages, institutions and handwriting. On the other hand scientists are needed for statistical analysis and climatological interpretation of the data. Worldwide, many thousand volumes with daily observations exist, but have not yet been analyzed for their climatic information. Let's get to work!

Meteorologische Zeitschrift, 1998

Meteorologische Zeitschrift, 1993

Scientific reports, Jan 6, 2018

A correction to this article has been published and is linked from the HTML and PDF versions of t... more A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Past Global Changes Magazine, 2014

Climate Dynamics, 2003

The interannual and decadal variability of summer (June to September) air temperature over the Me... more The interannual and decadal variability of summer (June to September) air temperature over the Mediterranean area is analyzed for the period 1950 to 1999. The combined influence of the large-scale atmospheric circulation at different levels and thermic predictors (thickness patterns and Mediterranean SSTs) on station temperature data is assessed by means of optimal objective techniques. The validity of the statistical models has been evaluated through cross-validation. Three large-scale predictor fields (300 hPa geopotential height, 700-1000 hPa thickness and SSTs) account for more than 50% of the total summer temperature variability. The positive phase of the first canonical mode is associated with blocking conditions, subsidence and stability related to warm Mediterranean summers. The second CCA mode shows an east-west dipole of the Mediterranean summer air temperature connected by a combination of a trough as well as an extended ridge over the western and eastern parts of the Mediterranean, respectively. Though both modes are found to contribute to long-term summer temperature trends in the 1950-1999 period, it is shown that the first canonical mode is mainly responsible for the 0.4°C warming (significant at the 95% level) over the last 50 years of the twentieth century. Further, the analysis reveals that the Mediterranean summer temperatures were higher in the 1860s, 1950s and 1990s and lower around 1910 and in the 1970s. A significant temperature increase of 0.5°C (0.27°C) is found for the 1900-1999 (1850-1999) period.

Climate Dynamics, 2003

The interannual and decadal variability of summer (June to September) air temperature in the nort... more The interannual and decadal variability of summer (June to September) air temperature in the northeastern Mediterranean is analysed for the period 1950 to 1999. Extremely hot and cool summers are illustrated by means of composite analysis. The combined influence of the large-scale atmospheric circulation and thermic predictors on local temperature is assessed by means of an objective approach based on empirical orthogonal functions and canonical correlation analysis. Monthly values of sea level pressure, geopotential heights, atmospheric thickness and Mediterranean sea surface temperatures are used as predictor fields and air temperature from 24 observational sites spread over Greece and western Turkey constitute the predictand variable. Results indicate that more than 50% of the total summer temperature variability can be explained linearly by the combination of eight large-scale predictor fields on two canonical correlation modes. The first canonical mode is related to a more meridional circulation at the upper tropospheric levels, which favours local land-sea contrasts in the associated local temperature pattern. Variations of this mode are found to be responsible for the occurrence of extreme events and decadal trends in regional temperature, the latter being characterized by a cooling in the early 1960s and a warming in the early 1990s. The second canonical mode pictures variations in the intensity of the zonal circulation over the Atlantic area that drive temperature anomalies affecting mainly the Aegean Sea and the west of Greece. Our results suggest the potential of statistical downscaling for Greek summer temperature with reliable climate forecasts for planetary-scale anomalies.

Quaternary Science Reviews, 2016

statistical correlations. Glacier retreat in the past 100e150 years corresponds to the anthropoge... more statistical correlations. Glacier retreat in the past 100e150 years corresponds to the anthropogenic global temperature increase. Many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain.

Environmental Research Letters, 2016

The spatial context is critical when assessing present-day climate anomalies, attributing them to... more The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal timescales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

Quaternary Science Reviews, 2011

The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustain... more The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed and presented in form of a Holocene Climate Atlas (HOCLAT; see http://www.oeschger.unibe.ch/ research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.

Informationen und Beiträge zur Klimaforschung Contributions à la recherche climatologique Luft-un... more Informationen und Beiträge zur Klimaforschung Contributions à la recherche climatologique Luft-und Satellitenbilder als mögliche Datenquellen bei der Schneekartierung Die Lufttrübungserscheinungen des Sommers 1783 in der Sicht schweizerischer Beobachter Untersuchungen über die Nebelhäufigkeit in Bern zwischen 1761 und 1969 Die Klimageschichte-eine vergessene Wissenschaft? / L'histoire du climat-une science oubliée?

Greenland ice core records show that, prior to the 20th century, temperatures during the Holocene... more Greenland ice core records show that, prior to the 20th century, temperatures during the Holocene in the Northern Hemisphere mid and high latitudes were only higher during the so-called “Holocene Climate Optimum”. Pollen analysis has demonstrated that this warmer period, also called “Atlantikum”, occurred in the Canadian Arctic, North Atlantic and Europe between approximately 8000 and 4500 cal yr BP. Glaciological evidence reveals that, during the mid-Holocene, the glaciers strongly retreated in the European Alps, the Canadian Rockies, in the Arctic and other regions of the northern hemisphere. Macrofossils bring evidences that the northern tree line moved north and was located at the Arctic coast over most of Russia. Antarctic ice cores show a widespread Holocene warm period between 11,500 and 9000 cal yr BP and secondary warmer phases in the Ross Sea sector (8000 – 6000 cal yr BP) and eastern Antarctica (6000 – 3000 cal yr BP). There is a lively debate whether the Holocene climate...

werden. Wir verstehen ihn hier als die Zeitperiode, in der sich die Randbedingungen des Klimasyst... more werden. Wir verstehen ihn hier als die Zeitperiode, in der sich die Randbedingungen des Klimasystems nicht mehr dramatisch verandert haben. Abbildung 1 zeigt die Meeresspiegelveranderungen in der sudlichen Nordsee wahrend der letzten 10 000 Jahre, wie sie von Karl-Ernst Behre vom Niedersachsischen Institut fur Kustenforschung ermittelt wurden. Daraus ist ersichtlich, dass die Abschmelzprozesse im Bereich der grosen Eisschilder, vor allem auf den Nordkontinenten Amerika und Eurasien, um zirka 6000 Jahre vor heute zum grosten Teil abgeschlossen waren. Damit haben wir die Gewahr, dass grosere Reorganisationen im Klimasystem, vor allem in Form von Veranderungen der thermohalinen Zirkulation im Ozean, bisher ausgeblieben sind. In diese Phase der letzten 6000 Jahre fallt zudem der starke Wandel mit dem Ubergang von den Jagern und Sammlern zur Sesshaftigkeit und schlieslich zum modernen Gesellschaftssystem. Wir beschranken uns deshalb auf diesen Zeitabschnitt, der neben der historischen au...

Nature Geoscience, 2018

In the version of this Article originally published, the 'Data availability' section contained an... more In the version of this Article originally published, the 'Data availability' section contained an incorrect DOI for data from the FLATS (XV) seismic network (

PAGES news, 2009

Towards a global synthesis of the climate of the last two millennia Workshop of the PAGES 2k Regi... more Towards a global synthesis of the climate of the last two millennia Workshop of the PAGES 2k Regional Network-Corvallis, USA, 7 July 2009 louiSe newman 1 , h. wanneR 2 and t. kieFeR 1

PAGES news, 2002

Before the advent of instrumental records, up to 20 observations a day were carried out at specif... more Before the advent of instrumental records, up to 20 observations a day were carried out at specific sites, by the same observer, following defined rules. Despite this plethora of data, many scientists are of the opinion that observations made before the instrumental period are "subjective" and less reliable than natural proxies. But these data were collected by very experienced scientists and observers. Once calibrated and verified in the present, the data are precise and have a spatiotemporal resolution unmatched by any other climate proxy data. They are probably the best data source for the reconstruction of climatic state parameters in continental areas for the period between 1500 and 1850. In addition, a worldwide data base of daily information is being put together for the worlds major oceanic areas from naval logbooks (project CLIWOC). Natural disasters are a major source of societal concern in the context of climatic change. However, the record of instrumental measurements is too short to explore natural patterns of disasters. This also holds for investigations into societal vulnerability. In this context, documentary evidence is invaluable. This issue of PAGES News mirrors the fact that investigations on documentary data are unevenly distributed on the globe. On one hand, this distribution is related to the abundance and availability of the data sources, which, in China go back for several thousand and in Europe for several hundred years. On the other hand, this kind of research has until recently been somewhat neglected in the Americas, where written sources begin with the European settlement. In Australia and in Africa records are almost absent. Curiously, hardly any research has been devoted to the Islamic world, despite its long standing tradition of keeping annals. Dealing with documentary data requires a historian's skills. Scientists tend to overlook the pitfalls inherent in this data and are usually not familiar with old languages, institutions and handwriting. On the other hand scientists are needed for statistical analysis and climatological interpretation of the data. Worldwide, many thousand volumes with daily observations exist, but have not yet been analyzed for their climatic information. Let's get to work!

Meteorologische Zeitschrift, 1998

Meteorologische Zeitschrift, 1993

Scientific reports, Jan 6, 2018

A correction to this article has been published and is linked from the HTML and PDF versions of t... more A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Past Global Changes Magazine, 2014

Climate Dynamics, 2003

The interannual and decadal variability of summer (June to September) air temperature over the Me... more The interannual and decadal variability of summer (June to September) air temperature over the Mediterranean area is analyzed for the period 1950 to 1999. The combined influence of the large-scale atmospheric circulation at different levels and thermic predictors (thickness patterns and Mediterranean SSTs) on station temperature data is assessed by means of optimal objective techniques. The validity of the statistical models has been evaluated through cross-validation. Three large-scale predictor fields (300 hPa geopotential height, 700-1000 hPa thickness and SSTs) account for more than 50% of the total summer temperature variability. The positive phase of the first canonical mode is associated with blocking conditions, subsidence and stability related to warm Mediterranean summers. The second CCA mode shows an east-west dipole of the Mediterranean summer air temperature connected by a combination of a trough as well as an extended ridge over the western and eastern parts of the Mediterranean, respectively. Though both modes are found to contribute to long-term summer temperature trends in the 1950-1999 period, it is shown that the first canonical mode is mainly responsible for the 0.4°C warming (significant at the 95% level) over the last 50 years of the twentieth century. Further, the analysis reveals that the Mediterranean summer temperatures were higher in the 1860s, 1950s and 1990s and lower around 1910 and in the 1970s. A significant temperature increase of 0.5°C (0.27°C) is found for the 1900-1999 (1850-1999) period.

Climate Dynamics, 2003

The interannual and decadal variability of summer (June to September) air temperature in the nort... more The interannual and decadal variability of summer (June to September) air temperature in the northeastern Mediterranean is analysed for the period 1950 to 1999. Extremely hot and cool summers are illustrated by means of composite analysis. The combined influence of the large-scale atmospheric circulation and thermic predictors on local temperature is assessed by means of an objective approach based on empirical orthogonal functions and canonical correlation analysis. Monthly values of sea level pressure, geopotential heights, atmospheric thickness and Mediterranean sea surface temperatures are used as predictor fields and air temperature from 24 observational sites spread over Greece and western Turkey constitute the predictand variable. Results indicate that more than 50% of the total summer temperature variability can be explained linearly by the combination of eight large-scale predictor fields on two canonical correlation modes. The first canonical mode is related to a more meridional circulation at the upper tropospheric levels, which favours local land-sea contrasts in the associated local temperature pattern. Variations of this mode are found to be responsible for the occurrence of extreme events and decadal trends in regional temperature, the latter being characterized by a cooling in the early 1960s and a warming in the early 1990s. The second canonical mode pictures variations in the intensity of the zonal circulation over the Atlantic area that drive temperature anomalies affecting mainly the Aegean Sea and the west of Greece. Our results suggest the potential of statistical downscaling for Greek summer temperature with reliable climate forecasts for planetary-scale anomalies.