Our different research projects cover the following periods:

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.(topics: Climate teleconnections, Intelligent archives)

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. During this time wine grapes were grown in Europe and southern Britain [1] [2] as they are today [3]. 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.

Example: Modelling climate response to historical land cover change: pdf (508 KB)

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. (topics: Climate Teleconnections)

Examples:

• Temperature trends: Globale räumlich-zeitliche Klimavariabilität im Holozän:
• Holocene climate variability as derived from alkenone sea surface temperature reconstructions and coupled ocean-atmosphere model experiments: pdf (828 KB)
• North Pacific and North Atlantic sea-surface temperature variability during the Holocene: pdf (1,1 MB)
• Acceleration technique for Milankovitch type forcing in a coupled atmosphere-ocean circulation model: method and application for the Holocene
  
• Arctic Oscillation signature in a Red Sea coral: pdf (292 KB) ps (972 KB)
• Impacts of the North Atlantic Oscillation and the El Nino-Southern Oscillation on Danube river streamflow variability. Rimbu, N., Dima, M., Lohmann, G., and Stefan, S., 2004: The impact of the North Atlantic Oscillation (NAO) and ENSO on the Danube river streamflow variability is investigated for the period 1840 to 1998. A composite analysis reveals that positive streamflow anomalies are related to a large scale atmospheric circulation pattern that contains elements of the positive phase of the Pacific North American (PNA) pattern and negative phase of the NAO. The corresponding sea surface temperature (SST) pattern shows positive anomalies over most of the tropical region. Opposite atmospheric circulation and SST patterns are associated to negative streamflow anomalies. Significant decadal variations of the NAO and ENSO impact on the Danube streamflow are detected for the observational period. A lag-correlation analysis reveals that winter SST from tropical Pacific and some regions from the North Atlantic are significantly correlated with the streamflow variations from spring and summer suggesting a possible predictive skill of the Danube streamflow anomalies in these seasons using winter SST as a predictor.
• Shift in ENSO teleconnections recorded by a Red Sea coral
• The Influence of Vegetation–Atmosphere–Ocean Interaction on Climate: pdf (400)
• Simulation of an abrupt change in Saharan vegetation: pdf (136)
• Carbon cycle, vegetation, and climate dynamics:Experiments with the CLIMBER-2 model: pdf (1,2 MB)
• Wie die Sahara zur Wüste wurde

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. (topics: Deglaciation)

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). (topics: Biosphere dynamics)

Example: Simulation of the global bio-geophysical interactions: pdf (672 KB)

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. (topics: Climate teleconnections)

Examples:

• Increased seasonality in Middle East temperatures during the last interglacial period
• Comparison of the last interglacial climate: pdf (580 KB)
• Transient simulation of the last glacial inception: Sensitivity and feedback analysis: pdf1 (432 KB), pdf2 (280 KB)
• Das Ende einer Warmzeit im Klimamodell: Poster (232 KB)

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. (topics: Deglaciation)

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. Some preliminary model results can be found here: Miocene ocean circulation and climate (pdf, 492 KB), Miocene marine carbon cycle (pdf, 684 KB). (topics: Ocean gateways)

Snowball earth (800-600 Mill. years ago)
Motivated by the extreme climates in the Earth's history, namely the full earth glaciation in the Neoproterozoic era (600-800 million years ago), known as "snowball" Earth, the atmospheric model is forced with extreme boundary and initial conditions. The impact of land albedo, oceanic heat transport, CO2 concentration, initial temperature conditions on the extreme climates are examined. (topics: Snowball earth)