Accurate climate modelling requires reliable estimations of climate sensitivity to CO2 forcing during past intervals of CO2 similar to those predicted. This entails an improvement of CO2 and sea surface temperature (SST) reconstructions, especially for tropical oceans. Widely-used paleothermometers such as UK’37, TEX86, foraminifer Mg/Ca and δ18O may not be accurate for absolute long-term SST in these regions. Therefore, coccolith clumped isotope thermometry (Δ47) is a promising tool to disentangle the especially problematic pre-late Miocene warm SST history of tropical oceans, improving our understanding of climate sensitivity and marine life to CO2 and allowing European and other countries to take wise and timely policy-related decisions and mitigation measures. This project aims to assess the presence of biological overprints (e.g. response to CO2 limitation) on coccolith Δ47 from cultures and coretop size fractions, develop an effective Δ47-SST calibration, validate the proxy by comparing Δ47-SST to a published reliable UK’37-SST record, and apply coccolith Δ47 to reconstruct absolute SST of Cenozoic tropical and polar oceans. This project combines the strong biological understanding of the proxy-encoding organism of the candidate and main supervisor, with the unique ability of the clumped isotope host group to achieve 1-2 °C precise Δ47 temperatures from 1-1.5 mg samples. This will allow to conclusively determine if there are vital effects in coccolith Δ47 and produce an unprecedented long-term tropical SST record for the pre-late Miocene. Implementing this project at the ETH Climate Geology group will enhance the candidate’s career via development of new scientific and analytical skills, while complementing and diversifying the research focus of the host group and enhancing Europe’s research excellence. To achieve highest impact, scientific peers, the local public, high school students and Europe parliamentarians related to climate change will be reached.