The temperature that kills people 65+ | Dr Mark Harber

Dr Mark Harber is a consultant nephrologist (kidney doctor) and the Royal College of Physicians' special adviser on healthcare sustainability and climate change. He's spent years working at the intersection of medicine and the environment as a member of the Sustainable Kidney Care committee, a clinical lead for the NHS London sustainability group, and an advisor to the UCL Partners Climate Collaborative. Now, he helps shape how the RCP advocates and lobbies on healthcare's role in the climate crisis. This conversation goes deep into the surprisingly stark relationship between heat and human health: why the death rate in London starts climbing at just 24 degrees, why 2026's June heatwave in the UK heatwave produced an estimated 2,900 excess deaths, and why chronic conditions from epilepsy to kidney failure get dramatically worse as the mercury rises. Mark explains why big national statistics can feel strangely meaningless next to a single hospital admission, and why he believes there's little point terrifying the public without giving them something practical to do about it. We talk about the NHS's own outsized carbon footprint (around 5% of the UK's total, more than the aviation industry) and why it became the first health system in the world to commit to net zero, back in 2019. Mark explains the hidden environmental cost of kidney dialysis, which can use 400 litres of water per session and carries 16 times the carbon footprint of an average NHS patient, and why the UK is on track to be 6 billion litres of water short every day by 2050. We also cover the less obvious ways climate change threatens healthcare itself: 90% of English hospitals at risk of overheating, a tenth to a third at risk of flooding, and disease-carrying mosquitoes now established in France and Italy that never used to survive this far north. —— Learn more about the RCP's Green Physician Toolkit at https://www.rcp.ac.uk/policy-and-campaigns/our-policy-priorities/climate-and-sustainability/green-physician-toolkit/ Find the National Emergency Briefing at https://www.nebriefing.org/ Find Real Zero's 7 Acts to Save the World at https://www.realzero.earth Subscribe to the Climate Unf*cked podcast at https://climateunfucked.substack.com/ And connect with me on LinkedIn at: /rob-coop https://www.linkedin.com/in/rob-coop/ —— Chapters 0:00 Why 24°C Already Raises the Death Rate 2:52 The Grim Maths Behind 2,900 Excess Deaths 4:17 Why Big Climate Numbers Feel Meaningless 6:20 Should We Be Scaring the Public About Heat? 8:13 The Delhi Cooling Rooms Saving Tuk-Tuk Drivers 10:41 Why Flights Are Up 80% in 20 Years 12:15 The Healthcare Sector Emits More Than Aviation 15:43 Why Institutions Fear the "Art of the Possible" 18:43 Why Your Dialysis Machine Has a Bigger Carbon Footprint 23:13 The Hospital Built to Handle Only 28°C 25:09 The Mosquito Bringing Dengue to Britain 27:35 Methane Is 80 Times Worse Than CO2 29:53 You're More Likely to Leave Your Partner Than Your Bank 33:18 Why Doctors Won't Sell You on Climate 37:12 How One Kilo of Plastic Costs Three of Oil 40:22 Why Politicians Won't Just Tell Us the Truth 44:50 The Hidden Kidney Risk in London's Air 49:43 The Hospital That Stopped Mowing Its Lawns 53:20 What Climate Activism Can Learn From Medicine 56:30 Why "What Can I Do?" Is Almost Enough 59:43 Tell Your Canvasser Climate Change Matters