A lecture by Professor William van Wijngaarden hosted by the Irish Climate Science Foundation (ICSF) on 25 November, 2020. Professor William van Wijngaarden is a Full Professor in the Physics Department at York University, located in Toronto, Canada. He received a PhD in Physics in 1986. His expertise includes analysing archival data of humidity, temperature and precipitation to detect any climate change. More recently, in collaboration with Professor William Happer, he is a pioneer in using radiative transfer to precisely calculate the forcing due to the various greenhouse gases. He has already published over 80 refereed articles relating to climate change.