Recent  

We studied the atmosphere-cryosphere interaction during the Last Glacial Maximum (LGM) in the Alpine region, using a high-resolution regional climate model. We analyzed the climate south and north of the Alps and provide a detailed map of the Alpine Equilibrium Line Altitude (ELA) as well as an analysis of the mechanism that sustained the Alpine glaciers at the LGM. Genoa low and a mild Mediterranean Sea led to frequent snowfall in the southern Alps, preserving the glaciers and lowering the ELA.

This study attempts to get a better understanding of the marine biological carbon pump and ecosystem functioning under warmer than today conditions. Our records from marine sediments show the Pacific tropical marine biological carbon pump was driven by variations in seasonal insolation in the tropics during the late Cretaceous and may play a key role in modulating climate and the carbon cycle globally in the future.

Ice core microparticle data typically use geometry assumptions to calculate particle mass and flux. We use dynamic particle imaging, a novel technique for ice core dust analyses, combined with traditional laser particle counting and coulter counter techniques to assess particle shape in the South Pole Ice Core (SPC14) spanning 50 – 10 ka. Our results suggest that particles are dominantly ellipsoidal in shape and that spherical assumptions overestimate particle mass and flux.

Understanding African climate change necessitates the study of geological data, some of the best of which comes from the sedimentary sequences of the Atlantic Ocean that preserve long records of dust blown from the continent. We use such a record to demonstrate that, depending on latitude, the monsoon responds differently to climate perturbations. This has implications not only for future environmental change but also for interpreting archaeological patterns of Middle Stone Age human groups.

We integrate our previous models to examine abrupt climate changes pertaining to Heinrich and Dansgaard-Oeschger cycles as well as deglaciation punctuated by Younger Dryas. We posit their common origin in the calving of ice sheet triggered by thermal switches at its bed, which are differentiated between that caused by geothermal heat and surface melt. Together with the ocean evolution toward maximum entropy production, the theory provides an integrated account of observed phenomena.

We study the behavior of the Atlantic Meridional Overturning Circulation (AMOC) in the mid-Pliocene. The mid-Pliocene was about 3 million years ago and had a similar CO₂ concentration to today. We show that the AMOC is stronger during this period due to changes in geography and that this has a significant influence on ocean temperatures and heat transported northwards by the Atlantic Ocean. Understanding the behavior of the mid-Pliocene AMOC can help us to learn more about our future climate.

We provide simple quantitative models for the interglacial and glacial intensities over the last 800,000 years. Our results suggest that the memory of previous climate states and the time course of the insolation in both hemispheres are crucial for understanding interglacial and glacial intensities. In our model, the shift in interglacial intensities at the Mid-Brunhes Event (~430 ka) is ultimately attributed to the amplitude-modulation of obliquity.

This study investigates the possibility to infer information on aerosol optical depth from photographs of historic paintings. The idea – which has been applied in previous studies – is very interesting, because it would provide an archive of the atmospheric aerosol loading covering many centuries. We show that twilight colours do not only depend on the aerosol optical thickness, but also on several other parameters, making a quantitative estimate of aerosol optical depth essentially impossible.

In this study, we develop the first tree-ring based precipitation reconstruction for the northern South American Altiplano back to 1625 CE. We established the significance of our reconstruction by using it to determine that the occurrence rate of extreme dry events together with a shift in mean dry conditions for the late 20th-beginning 21st century is unprecedented in the past 389 years. Our reconstruction provides also valuable information about the ENSO influences in the local precipitation.

This manuscript presents a compilation of high resolution (11 cm) water isotopic records including published and new measurements over the last 800 000 years on the EPICA Dome C ice core, Antarctica. Using this new water isotopes (δ¹⁸O and δD) combined dataset, we study the variability and possible influence of diffusion at multi-decadal to multi-centennial scale. We observe a stronger variability on the onset of the interglacial interval corresponding to a warm period.

We digitized dozens of weather journals containing temperature measurements from in and around Bern and Zurich. They cover over a century before the creation of a national weather service in Switzerland. With these data we could create daily temperature series for the two cities that span the last 265 years. We found that pre-industrial climate on the Swiss Plateau was colder than suggested by most existing temperature reconstructions and almost 3 °C colder than present-day climate.

Understanding why the past 800 thousand years of Earth’s history has been paced by ~100 thousand-year cycles of alternating cold glacial and warm interglacial conditions remains a major scientific debate. To contribute knowledge to this question, we studied well-preserved glacial deposits in eastern Patagonia. Our work provides a new detailed glacier chronology that enables to establish the timing of multiple Patagonian ice-sheet expansion events over the last three hundred thousand years.

To look at climate over the past 12000 years, we reconstruct spatial temperature using natural climate archives and information from model simulations. We see mild global mean warm around 6000 years ago, which differs somewhat from past reconstructions. If more of our data represents summer values, this could explains some of the observed temperature change, but it still wouldn't explain the large difference between many reconstructions and climate models over this period.

In some situations, the color of sediment records information about the climatic conditions under which it was deposited. We show that sediment color and climate are linked at Lago Argentino, the world's largest ice-contact lake, but that this relationship is too complex to be used for reconstructing past climate. We instead use this sediment color-climate relationship to show that temperature and wind speed affect sediment deposition in the summer, but not in the winter.

A mismatch between model- and proxy-based Holocene climate change may partially originate from the poor spatial coverage of climate reconstructions. Here we investigate quantitative reconstructions of mean annual temperature and annual precipitation from 1676 pollen records in the Northern Hemisphere. Trends show strong latitudinal patterns and differ between (sub-)continents. Our work contributes to a better understanding of the global means.

Did climate or humans caused glacial/interglacial vegetational re-constellations in Australia, and the extinction of the exotic megafauna at ~43 ka BP? We highlight the role of the rapidly varying Leeuwin Current for the Australian ecosystem change. We note that the concerted action of a weakening Leeuwin Current, the ecological response, and human interference enhanced the ecological stress on the megafauna until a tipping point was reached, after which faunal recuperation no longer took place.

Despite its importance in global climate, our knowledge of Antarctic sea-ice changes throughout the last glacial-interglacial cycle is extremely limited. As part of the Cycles of Sea Ice Dynamics in the Earth system (C-SIDE) Working Group, we here review marine- and ice core-based sea-ice proxies to provide insigths in their applicability and limitations. By compiling published records, we provide information on Antarctic sea-ice dynamics over the past 130,000 years.

The sensitivity of climate to the height changes of East Antarctic ice sheet (EAIS) during the mid-Pliocene has been conducted using the HadCM3 model. The results show that the height reduction of EAIS leads to a warmer and wetter East Antarctica. However, unintuitively, both the surface air temperature and the sea surface temperature decrease over the rest of the globe. These findings could provide insights into future changes caused by warming-induced decay of the Antarctic ice sheet.

Extremes of sea level at the coast are mostly generated by the temporary surges of ocean water associated with storms. It would be very valuable to understand how a changing climate will affect the occurrence of storms and thus coastal sea level extremes, but uncertainties are large. To increase our knowledge in this field, we adopt a modeling approach to study sea level extremes in a past period of climate that was warmer than the present, the Last Interglacial.

Based on proxy data and modeling, the Arctic temperature has an asymmetric cooling trend with more cooling over the Atlantic Arctic than the Pacific Arctic during the Holocene, dominated by orbital forcing. There is a seasonal difference in the asymmetric cooling trend, which is dominated by the DJF temperature variability. The Arctic dipole mode of sea level pressure and sea ice play a major role in asymmetric temperature changes, which is possibly modulated by orbital forcing of PDO.

Understanding the hydrological changes on the Tibetan Plateau (TP) during the mid-Holocene (MH; a period with warmer summers than today) will help understand the expected future changes. This study analyses the hydroclimates over the headwater regions of three major rivers originating on the TP, using dynamically downscaled climate simulations. Model-data comparisons show that the dynamically downscaling significantly improves both the present-day and MH regional climate simulations on the TP.