Research

Research interests
General Approach
Research Group
Selected Research Topics and Projects
Further Information on selected Topics

Research interests


"looking at the past sharpens our understanding of possible future climate changes"

It is of vital importance to understand how increasing human population and industrialization have already caused significant changes in earth's climate. In order to properly address this question, one needs quantitative information regarding the amplitude and rapidity of natural variations in the ocean, over the continents, and in the cryosphere. The best way to ascertain the extent of past changes is through the inspection of historical time series of direct temperature measurements. Information regarding the pre-anthropogenic state of the system can be obtained either from proxies that record past climate and environmental conditions, or by simulating climate using comprehensive models under external forcing.

One special area of my research is therefore focused on Earth system modeling, paleoclimate variability, and theoretical aspects in Earth system analysis. Particular aspects are the role of the global ocean circulation, and the dynamical interpretation of paleoclimate data, e.g. corals, ice cores, and marine sediments. Analyzing reconstructed paleoclimate records and models allows for the evaluation of forcing and feedback mechanisms in past and future climate changes. In return, model simulations can aid in the interpretation of the causes of observed variations in paleoclimate data.

Paleoclimate dynamics contextualises current and future changes, quantifies natural variability, and informs us about mechanisms under various forcings. One key method is through model - data comparisons (out-of-sample evaluation, emergent constraints).




​ General Approach

Climate change is one of the most pervasive and threatening issues of our time, with far-reaching impacts in the twenty-first century. Climate change is expected to have unprecedented implications on where people can settle, grow food, build cities, and rely on functioning ecosystems for the services they provide. In many places, temperature changes and sea-level rise are already putting ecosystems under stress and affecting human well-being. (UN Environment)

The grand aim of all science is to cover the greatest number of empirical facts by logical deduction from the smallest number of hypotheses or axioms.
(Albert Einstein)

Science is intended to deepen our understanding of the natural world. Progress in science arises from the tension between induction and deduction, empiricism and theory. Data gathered through observation and experimentation provide clues about the structure and function of the natural world, and theory organizes existing data and new ideas into a cohesive conceptual framework to both explain existing observations and make novel predictions. Theory reduces the apparent complexity of the natural world, because it captures essential features of a system, provides abstracted characterizations, and makes predictions for as-yet unobserved phenomena that additional data can be used to test. And about this you can not wonder enough.




Research Group


Paleoclimate Dynamics research group at AWI
Motto: The analysis of past variations shall broaden our view of the climate system and restructure our approach to a more comprehensive theory of climate.

Our research focuses on the analysis of different climate conditions in the past and the identification of driving mechanisms causing climate change. Special research topis are feedback mechanisms in the climate system, the role of the global ocean circulation for climate variations, a better understanding of previous glacial times and warm stages as well as the climate of the Holocene. In our studies, we use different models of the Earth system and statistical methods to analyse instrumental and proxy data.

Without models, we cannot grasp the interrelations in the system or explain the phenomena we observe. I work with Earth system models. My priority in doing so is to obtain the broad range of solutions and uncertainties in the climate system, as well as its variability over timespans ranging from days to several million years. The latter aspect includes alternating glacial and interglacial periods, the climate’s sensitivity to external forcing, and the climatic trends of the past few millennia. In addition, we develop prognoses for as yet unseen factors and make estimates for future climate conditions. Our goal is to use Earth system models for all time scales – and from the past to the future. Depending on the specific question at hand, we include new Earth system components. For instance, we’ve recently begun using ice sheet models that provide insights into sea level variations. What fascinates me most are the feedback loops in the Earth system. Models allow usto develop new ideas and hypotheses and to test them. To do so, we not only have to understand the model but also consider suitable boundary conditions and climate simulations.





Selected Research Topics and Projects





Further Information on selected Topics

The Instrumental Record (last 150 years)
The earliest meteorological records of measured temperatures and pressure are from Western Europe beginning in the late 17th and early 18th centuries. The number of stations increased since that time and by the early 20th century, data is collected in almost all regions, except for Polar Regions where collections began in the 1940s and 1950s. Global or hemispheric trends based on the observed data of the last 140 years inherit still some uncertainties, mostly due to data gaps in space and time, but also from instrumental errors. During the last years Satellite measurements are available and have been used to reconstruct global atmospheric temperatures back from the late 1970th. Existing observations from the 1950th onward are used in Reanalysis projects like the ones from NCAR/NCEP or ECMWF to create consistent data sets for most atmospheric properties.



Historical period (last 1000 years)
In assessing the significance of recent global warming and in particular in considering the attribution of recent climate change, the question of how much temperatures have varied over the last millenia or more arises. In this context, the best known fluctuations are the Medieval Warm Period and Little Ice Age. The "Medieval Warm Period (MWP)" or "Medieval Climate Optimum" was an unusually warm period during the European Medieval period, lasting from about the 10th century to about the 14th century. The "Little Ice Age" (LIA) was a period of cooling lasting approximately from the mid-14th to the mid-19th centuries. This cooling brought an end to an unusually warm Medieval climate optimum. There were three maxima, beginning about 1650, about 1770 , and 1850 , each separated by slight warming intervals. Initial research on the MWP and LIA was largely done in Europe, where the phenomenon was most obvious and clearly documented. The Vikings took advantage of ice-free seas to colonize Greenland and other outlying lands of the far north. The period was followed by the Little Ice Age, a period of cooling that lasted until the 19th century when the current period of global warming began.


Holocene (last 10,000 years)
To observe a Holocene environment, simply look around you! The Holocene is the name given to the last ~10,000 years of the Earth's history -- the time since the end of the last major glacial epoch, or "ice age." Since then, there have been small-scale climate shifts -- notably the "Little Ice Age" between about 1200 and 1700 A.D. -- but in general, the Holocene has been a relatively warm period in between ice ages. It followed the Last Glacial Maximum and the subsequent deglaciation. At the early to mid-Holocene, the Earth's orbital parameters were such that insolation allowed for warmer and wetter than present summers in large parts of the northern hemisphere. Geological data in general indicate, among other things, a retreat of Arctic sea ice, an expansion of boreal forest, as well as a vegetated Sahara. The rather gradual climate 'deterioration' in the northern hemisphere was interrupted by several abrupt events. The most pronounced cooling event happened at around 8,200 years before present when a sudden freshwater pulse from a meltwater lake to the south of the Laurentide ice sheet temporarily diluted the Atlantic ocean circulation. These effects have been described in different paleoclimate modeling studies. For a simulation of the last 1,000 years, in particular, also prescribed changes in the solar forcing, atmospheric trace gases, volcanism, and human impacts (mainly deforestation) have been taken into account. However, many open questions still exist with respect to the interpretation of different geological proxies for the Holocene. This concerns for example the origin of short-term variability in the data, descrepancies in different data sets, or reasons behind teleconnections. Here, Earth-system models can help to better understand the geological evidence.

Deglaciation (20,000-9,000 years ago)
Around 14.000 years ago there was a rapid global warming and moistening of climates, perhaps occurring within the space of only a few years or decades. In many respects, this phase seems to have resembled some of the earlier interstadials that had occurred so many times before during the glacial period. Conditions in many mid-latitude areas appear to have been about as warm as they are today, although many other areas - whilst warmer than during the Late Glacial Cold Stage - seem to have remained slightly cooler than present.

Last Glacial Maximum (21,000 years ago)
During the last glacial cycle, which started with the end of the Eemian interglacial, northern hemispheric ice sheets were generally increasing in size reaching their maximum extent at the so-called Last Glacial Maximum (LGM). At that period, the ice sheets were spread not only over vast areas in Northern America. Also in Europe, they covered Scandinavia and large parts of Britain and northern Germany. In general, climate was not only colder but also drier in many parts of the world. The sea-level was about 120 m lower than today, the CO2 level was as low as about 190 ppmv. Tropical rain forests and boreal forests were substantially reduced in size. Maximum glaciation was followed by a very rapid deglaciation. The LGM has been investigated in a large number of data as well as modeling research projects (e.g. CLIMAP, GLAMAP, BIOME6000, PMIP).


Eemian "Interglacial" (131,000-114,000 years ago)
The Eemian began about 131,000 YBP and ended around 114,000 YBP. In broad outline, the Eemian interglacial consisted of an early warm period of about 3,000 to 4,000 years duration, a rapid cooling, and then a much slower cooling leading to the next glacial episode.

Late Quaternary (last 1 Mill. years)
The Quaternary is the second period of the Cenozoic era, following the Tertiary; also, the corresponding system of rocks. It began two to three million years ago and extends to the present. It consists of two grossly unequal epochs: The Pleistocene, up to about 8,000 years ago, and the Holocene since that time. The Quaternary was originally designated an era rather than a period, with the epochs considered to be periods, and it is still sometimes used as such in the geologic literature. The Quaternary may also be incorporated into the Neogene, when the Neogene is designated as a period of the Tertiary.

Miocene (24-5 Mill. years ago)
In the Miocene (about 24 - 5 million years ago), the world has almost assumed a modern continental configuration. However, there are still open ocean gateways connecting the Atlantic with the Pacific, and the Eurafrican Mediterranean Sea with the Indian Ocean (more info on Paleomap project). At the middle to late Miocene transition, there is evidence for drastic and repeated reorganizations of the marine carbon cycle and for global climatic changes. We investigate the reasons of these changes. Out working hypothesis is that the closure of the ocean gateways at that time led to the establishment of the modern ocean overturning circulation pattern. This in turn affected the marine carbon cycle as well as the global climate.