As a previous vice-chair of the IPCC, Van Yp (as he is called by his peers) is one of the forerunners of climate change mitigation through strong decrease of fossil fuel consumption.

At the initiative of professor André Berger the Institut d’Astronomie et de Géophysique Georges Lemaître of the UCLouvain had started to study the impacts of changes in concentration of greenhouse gasses on the evolution of the Earth's climate.

[3] van Ypersele received a PhD in physics from UCLouvain in 1986 (with highest honours), with his dissertation on his work done at the United States National Center for Atmospheric Research (NCAR) on the effect of global warming on Antarctic sea ice.

[2] Promoters of his PhD were professors André Berger (UCLouvain) and Albert Semtner[4] (National Center for Atmospheric Research and Naval Postgraduate School in the United States), one of the developers of the Modular Ocean Model.

He contributed to a short sentence that entered in the annals of the organisation: The balance of evidence suggests that there is a discernible human influence on global climate.

This statement is crucial, as it mentions clearly for the first time that a worrying climate evolution is ongoing; it is demonstrated and no longer a theoretical projection of the future.

[5] He developed his qualities as negotiator at about all Conferences of the Parties (COP) of the United Nations Framework Convention on Climate Change, for over 20 years.

[2][3] At such climate summits the Belgian delegation strongly benefited from the scientific advice and dedication of prof van Ypersele.

[10] The UN Secretary General appointed him in 2016 as a member of a 15-member group of scientists[11] tasked with the preparation of the first quadrennial Global Sustainable Development Report.

Despite the assistance and official support of the Belgian government, his campaign pledge to maintain the scientific independence of the IPCC, and his stressing of the importance of inclusiveness and communication,[16] Jean-Pascal van Ypersele was not elected.

In a 2018 Associated Press interview, van Ypersele urged that "countries should do everything possible to work towards the report's goal of reining in carbon emissions by 2030, at which point scientists say damage to the climate will be irreversible unless urgent action has been taken."

"[53] Van Ypersele's work is sometimes challenged by “climate confusers”; there was a petition signed by eight Belgian academics and opinion makers opposing his candidacy as IPCC chair in 2015.

[54] Most known of these opponents is his colleague from UCLouvain, Professor István Markó [fr] who produced a large scientific output in the field of organic chemistry, but not climatology.