How much do humans contribute to today's climate change? This is one of research's central questions. To give a proper answer, we have to know the parameters of natural variability, e.g. the temperatures in oceans, above the continents and in polar regions. This necessitates considering the properties of the climate of the past. We are able to reconstruct past climate changes from historical data collections or by evaluating documented observations.
The history of Earth provides us with different climate states that help us to better understand a climate in change. This acrylic painting below shows an example of a very warm climate from about 90 Million years ago when parts of Antarctica were covered by temperate, swampy rainforests.
However, existing data collections, which allow the quantification of climate change at global scale (e.g. satellite-based observations), are too short and already underlie the strong influence of humans on the natural conditions. To understand the climate system prior to anthropogenic influence, we have to follow another path and employ methods of paleoclimatology. Proxies provide data that is representative for past climates and can be derived, e.g., from isotopic composition of ice-cores and tree rings. These are key to reconstruct climate and environmental conditions of even the distant past. Complex numerical models of the climate system enable us to explore and understand the processes that shaped past climates. If applied in combination, climate archives and climate models provide us with an excellent test bed for a better understanding of climate variability of the past and to explore thresholds and tipping points that may become defining for our future in a warming world.
In our research we link past climates to environmental conditions of the future. This implies that we research the state of the Earth System over a time span of several tens of millions of years. While we employ a diverse approach, the following time scales are of special interest for our study of climate variability and climate change: Historical to Present to Future, Quaternary, and pre-Quaternary.