Jonathan Cullen is a Professor of Sustainable Engineering at the University of Cambridge. He leads the Resource Efficiency Collective and has a reputation for top-down studies of resource systems, bringing skills in developing new metrics to reflect both energy and material consequences of materials production. Jonathan's research interests span energy and material systems, efficiency limits, circularity and zero carbon transition pathways. He led the project C-THRU: carbon clarity in the global petrochemical supply chain (c-thru.org) and has been a co-investigator on: CCG: Climate Compatible Growth (climatecompatiblegrowth.com), TransFIRe (transfire-hub.org), S2uPPlant, and UK FIRES (ukfires.org). He was a Lead Author for the IPCC AR6 Industry Chapter and co-authored the book Sustainable Materials: with both eyes open, which pioneered the concept of material efficiency for energy-intensive industries.