Geert Jan van Oldenborgh obtained a PhD in the phenomenology of elementary particles at the University of Amsterdam in 1990, supervised by J. Vermaseren. After three post-doc positions in this field he switched to climate research. His first research topics were El Niño and data assimilation. This naturally led to research into seasonal predictability and the KNMI Climate Explorer web-based climate analysis tool, now as senior researcher at KNMI. As the skill of seasonal forecasts in Europe is mainly determined by the trend he also started research into regional climate change projections and trend verification. This extended into verification of decadal forecasts. He was Lead Author of the IPCC WG1 AR5 report (Chapter 11, Near-term projections and predictability, and Annex I Atlas). After a year of illness he is now mainly active in extreme event attribution, which combines elements of seasonal forecasts, regional climate change and verification.
Geert Jan van Oldenborgh passed away in October 2021.