The proposed project aims to investigate and understand the development of seasonality in terrestrial ecosystems of Northern Hemisphere during the last 23 million years, which caused massive ecosystem transformations, such as the spread of grasslands over large fractions of the globe. The project will concentrate on giving the researcher, Jussi T. Eronen, training in vegetation modelling and understanding of isotope analysis to enable him to work fluently within both modeling and proxy data communities. There are two main components that constitute this project: Global-scale vegetation modelling (first objective), and synthesis of vegetation modelling with fossil and isotopic paleoenvironmental data (second objective). Main research tools are dynamic vegetation modelling, fossil data, and isotope records. The project innovatively uses the fossil data to derive proxy estimates of the key environmental variables such as Net Primary Production, temperature, precipitation and seasonality. The original approach in this project is to merge vegetation modelling seamlessly with fossil data and stable isotope records to synthesize available information. Aim is to gain insight into interactions of biotic and abiotic systems on long (geological) timescales. As a result, we can investigate the biological dynamics of pre-Quaternary times at a global scale and identify critical transitions and thresholds in the past. This project increases our understanding of the processes by which terrestrial ecosystems respond to increased seasonal variations of climate. It is directly related to one of the major societal challenges in the Mediterranean region, the projected impact of current climate change on heat waves, and increased rainfall seasonality. This project establishes Eronen as one of very few people in the palaeo-community who can work with actual fossil data, derive variables based on fossil data as well as design modelling scenarios based on fossil data and perform modelling.