It is of vital importance to understand whether increasing human population and industrialization have already, or have the potential to, induce significant changes in earth's climate that may threaten health, security and prosperity of human populations. In order to properly address this question, we need 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 measurements or documentation of such environmental observations. Unfortunately, the type of direct measurement records which would allow us to quantify climate changes on a global scale are too short, and they fall already within the period of strong human impact on natural conditions. We therefore widen our perspective to the study of the Holocene. This geologic epoch represents the current interglacial after the end of the last glacial and the subsequent deglaciation. During the Holocene modern humans have experienced various swings in climate conditions, and past societies have had to either adapt or to perish. We can study variability of climate during the Holocene towards relating modern human-influenced climate change to natural variations that would occur even if humans were absent. Information regarding the pre-anthropogenic state of the Holocene can be obtained either from proxies that record past climate and environmental conditions, or by simulating climate using comprehensive models of the climate system under appropriate external forcing changes.
The paleoclimate record provides a long-term perspective of climate variability and an excellent test bed for models. We can verify the skill of climate models employed for projections of a future warm world against model-independent inference of natural variability in the current interglacial.
Various statistical and numerical tools and various types of data sets are employed by us in our research. Historical and reanalysis data help us to explore links between atmospheric circulation and sea surface temperature patterns that shape a substantial portion of nature variability like the El Nino Southern Oscillation. One objective of such studies is to understand the teleconnections (i.e. far reaching effects of natural climate variability) that control the low frequency variations in the proxy records. In the ideal case, the method provides for a reconstruction of climate modes beyond the instrumental record and thereby helps us to link pre-observational to observed climate variability. As a result we can set climate shifts, like those observed in the 1970s, into a long-term context. Proxy data and simulations of Holocene climate evolution can provide estimates of natural climate variability in the pre-industrial era and may refine our expectation of environmental influence on humans in a warming climate.
