Hans-Otto Pörtner is a leading animal physiologist based at the University of Bremen and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Germany, who first published in Journal of Experimental Biology in 1986. Since then, he has specialised in the physiology of marine vertebrates and invertebrates, with an interest in the impact of hypoxia and temperature on survival, developing the concept of oxygen- and capacity-limited thermal tolerance. It was Pörtner's work on the impact of rising CO2 levels on marine organisms that brought him to the attention of the Intergovernmental Panel on Climate Change (IPCC) when governments were considering storing CO2 in the deep oceans. Contributing to the IPCC Special Report on Carbon Dioxide Capture and Storage in 2005, Pörtner was part of the team that led to the prohibition of CO2 dumping in the oceans in 2007. This resulted in Pörtner being invited to contribute to the planning process for the IPCC's Fifth Assessment Main Report, approved by the IPCC in 2014, which stated that human CO2 emissions are 'extremely likely' to be the dominant cause of global warming and its impacts. In 2015, Pörtner was voted co-chair of the IPCC Working Group II, assessing the planet's vulnerability to climate change, culminating in the Sixth Assessment Synthesis Report released in 2023. Pörtner is co-presenting the Climate and Biodiversity Plenary Lecture on 25 March 2025 at the Biologists @ 100 conference, hosted by The Company of Biologists. Here, he reflects on his career, his contribution to the IPCC and how to minimise our impact on the planet.