One of Australia’s leading climate scientists, Prof Will Steffen, died in January. Steffen has been hailed as a brilliant climate thinker, selfless mentor and gifted communicator. His death is a great loss to climate science and understanding of earth systems.

Some of his friends and colleagues wrote about their relationship with Will in an article in The Conversation, published on 31 January.

Will joined the CSIRO as an editor and information officer but he was soon headhunted to the nascent International Geosphere Biosphere Program, an international consortium of scientists which aimed at understanding the physical, chemical and biological processes that regulate the whole Earth system. He eventually served as the IGBP’s executive director from 1998 to 2004.This was the early 1980s, when the field now known as Earth system science was just taking off.

Will was a visionary in many ways. He understood that the environmental problems we were trying to solve spanned many academic disciplines and were deeply interconnected. Few people had his ability to absorb so many diverse types of science and to work with the diverse research communities whose expertise was urgently needed as part of the solutions.

Will co-developed a number of influential ideas in sustainability science, such as:

• The planetary boundaries framework that shows us that the environment is not boundless and elastic and able to absorb all that we throw at it or take from it. Our planet has limits – and if we push too far, we will break something, leading to dramatic changes to the planet.
• The concept of the Great Acceleration which describes the dramatic increase in human environmental impact since the 1950s, brought about by population growth and fossil-fuel burning.
• The concept of the Anthropocene (that the planet has entered a new geological epoch because of human activity).

Viewing the world in this way helps us understand what we have done to our environment – and how to begin fixing the problems.

In 2011, he was appointed to the Australian government’s Climate Commission, which was dedicated to deepening public understanding of climate change and its impacts. When commission was abolished by Tony Abbott in 2013, Steffen co-founded the Climate Council of Australia to continue the work, funded by public donations. They raised $1 million in a week! Will authored, reviewed and publicly launched numerous reports that clearly explained to the public the risks and dangers of climate change.

Will Steffen epitomised the ethos of a social contract between scientist and society in his pursuit and sharing of knowledge relevant to the grand challenge of climate change. His visionary academic publications represent a track record of which any scientist would be proud, but his even greater legacy is the thousands of people he educated and inspired to work for a better future. From Nature 615, 29 (2023)