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L5 Public Health Global environmental changes _ health

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aliasesL5 Public Health Global environmental changes _ health

16 min read

Overview

This lecture frames climate change and environmental degradation as a global health emergency and a professional responsibility for doctors. It moves from the science of planetary limits (planetary boundaries, doughnut economics) through the mechanisms and inequities of climate-related health harm, to emissions data and mitigation pathways (global, NZ), the health-equity co-benefits of mitigation, health-sector adaptation, and finally concrete examples of NZ clinicians and students acting on climate and health.

Professional responsibility

Medical bodies frame environmental and climate action as part of the physician’s role, not an optional extra:

  • The medical profession and individual physicians have roles in public health, environmental protection, law, and testimony at judicial proceedings.
  • WMA Declaration on the Rights of the Patient: when legislation, government action, or any institution denies patients their rights, physicians should pursue appropriate means to assure or restore them.
  • Australasian Medical Colleges accreditation standards (Domain 3): graduates must recognise the diverse needs of patients in communities across Australia and Aotearoa New Zealand, understand the underlying social and environmental determinants of health, apply strategies addressing health inequities, and be committed to advocacy that influences system-level change in a socially accountable and environmentally sustainable manner.

Planetary boundaries and doughnut economics

The planetary boundaries framework tracks how far human activity has pushed Earth systems beyond safe operating limits, assessed across domains including climate change, biosphere integrity, land-system change, freshwater use, biogeochemical flows, ocean acidification, atmospheric aerosol loading, stratospheric ozone depletion, and (from 2023) novel entities.

  • 2009: 7 boundaries assessed, 3 crossed.
  • 2015: 7 boundaries assessed, 4 crossed.
  • 2023: 9 boundaries assessed, 6 crossed.
  • 2025: 9 boundaries assessed, 7 crossed.
  • Trend: an increasing number and severity of boundary transgressions over time.

Doughnut economics (Raworth) combines this with a social floor: the inner ring is the social foundation (shortfall), covering water, food, health, education, income & work, peace & justice, political voice, social equity, gender equality, housing, networks, and energy. The green ring is the ecological ceiling; beyond it, in “overshoot,” are climate change, ocean acidification, chemical pollution, nitrogen & phosphorus loading, freshwater withdrawals, land conversion, biodiversity loss, air pollution, and ozone layer depletion. [flag: a second citation/URL beneath the Raworth citation was cut off and not fully legible]

The evidence and framing of climate change

“Six truths about climate change” (Badullovich et al 2025) is presented as a framework that predicts policy support, discussion, and political advocacy:

  1. It’s real — climate change is happening.
  2. It’s us — human activity is causing it.
  3. Experts agree — there is scientific consensus on human causation.
  4. It’s bad — climate change harms people.
  5. Others care — most people are concerned and support action.
  6. There’s hope — actions can limit the harm.

A BMJ 2014 editorial (“Climate change and human survival”) is used to frame the IPCC’s findings as showing the need for “radical and transformative change,” describing climate change as a global health emergency: those who care for the health of people have perhaps the greatest responsibility to act, and immediate, transformative action is needed at every level — individual, local, national; personal, political, financial. [flag: part of the editorial’s closing sentence is cut off at the slide edge, and the byline/author affiliations are too small to read]

Health impacts of climate change

Four central climate drivers — rising temperatures, more extreme weather, rising sea levels, increasing CO2 levels — are linked to exposure categories and their associated health effects:

  • Extreme heat → heat-related illness and death, cardiovascular failure.
  • Severe weather → injuries, fatalities, mental health impacts.
  • Air pollution → asthma, cardiovascular disease.
  • Changes in vector ecology → malaria, dengue, encephalitis, hantavirus, Rift Valley fever, Lyme disease, chikungunya, West Nile virus.
  • Increasing allergens → respiratory allergies, asthma.
  • Water quality impacts → cholera, cryptosporidiosis, campylobacter, leptospirosis, harmful algal blooms.
  • Water and food supply impacts → malnutrition, diarrhoeal disease.
  • Environmental degradation → forced migration, civil conflict, mental health impacts.

Global injustice: who bears the burden

The health harms of climate change fall disproportionately on people who contributed least to causing it.

  • 2024 Lancet Countdown data on heat-related mortality in adults over 65 (comparing 1990-99 with 2014-23, against a counterfactual of no temperature change) show the largest percentage increases in low- and middle-income countries in Africa, South America, the Middle East, and parts of Asia, versus smaller increases in North America, Europe, Australia and NZ. [flag: exact per-country percentage values not legible at the source resolution]
  • Springmann et al (2016): modelled additional deaths (thousands) from climate-driven changes in food production, by cause (underweight, fruit and vegetable consumption, red meat consumption, overweight, obesity). Globally, a large positive contribution from reduced fruit and vegetable consumption is partly offset by negative contributions from obesity and red meat consumption, giving a net total of roughly 500,000 additional deaths (gross total scaled to ~800,000). By region, LMICs of Southeast Asia and the Western Pacific show the largest positive net totals (driven mainly by underweight and reduced fruit/vegetable consumption), while high-income countries and LMICs of Europe show smaller, near-zero, or negative net totals (driven by reductions in obesity and red meat consumption). [flag: precise numeric values per region not legible]
  • IPCC AR6 data on historical per-capita emissions versus development (1870-2014) show high-income countries with disproportionately high per-capita emissions relative to their development level (e.g. Australia/NZ ~21 t CO2-eq/capita, USA/Canada ~19 t CO2-eq/capita), while many lower- and middle-development regions (parts of Africa, South Asia) sit at 0-4 t CO2-eq/capita. A “Sustainable Development Pathways” trajectory is proposed toward a “Sustainable Development Corridor” of high development achieved at low, and eventually net negative, per-capita emissions — i.e., development does not have to require high per-capita emissions.
  • IPCC 2018 special report (1.5°C): global CO2 emissions rose historically from ~15 GtCO2/yr (1980) to a peak of ~42 GtCO2/yr (~2020). Two modelled pathways to net zero are shown, one reaching net zero by 2040 and one by 2055. Cumulative emissions rose to roughly 2000-2500 GtCO2 by 2020; the earlier net-zero pathway (2040) levels off at ~2650 GtCO2 cumulative, versus ~3000 GtCO2 for the 2055 pathway — earlier action yields substantially lower cumulative emissions.
  • Political barriers to mitigation: at COP29 (Baku, 2024), over 1,700 coal, oil and gas lobbyists were granted access, outnumbering the delegations of almost every country; Azerbaijan’s deputy energy minister and COP29 chief executive was filmed agreeing to facilitate oil deals during the talks. Cited as evidence that “COP summits are no longer fit for purpose” according to climate policy experts.
  • NZ emissions sources: Energy 37.9%, Agriculture 53.0%, Industrial processes and product use 5.1%, Waste 4.0%. Agriculture breaks down into dairy cattle 26.0%, sheep 11.9%, beef cattle 10.8%, other 4.3% (each split further into methane and nitrous oxide contributions). Unusually for a developed country, agriculture rather than energy is NZ’s largest emissions source.
  • World emissions sources (direct emissions by sector, 59 GtCO2-eq total): buildings 5.6%, transport 15%, agriculture/forestry and other land use (AFOLU) 22%, industry 24%, other energy 10%, electricity + heat 23% (of which industry accounts for 43.0% and buildings 46.9% of electricity+heat use). [flag: some percentage labels on this chart were very small and hard to confirm precisely]
  • NZ government climate policy: described as concerted government inaction, with failure by both major parties but specific criticism of the current coalition for climate policy repeals, the Regulatory Standards Act, the Fast Track Approvals Act, and environmental law reform. NZ’s gross emissions (excluding LULUCF) rose from ~68,000 kt CO2-eq (1990) to a peak of ~85,000 kt CO2-eq (~2005-06), declining to ~76,000 kt CO2-eq by 2024. Net emissions (including LULUCF) rose from ~44,000 kt CO2-eq (1990), spiked to ~65,000 kt CO2-eq (~2006), then fluctuated between ~52,000 and 61,000 kt CO2-eq, ending around ~55,000 kt CO2-eq in 2024.

Mitigation with health equity co-benefits

Four mitigation measures are highlighted as bringing health and health-equity co-benefits alongside emissions reduction: low-carbon public and active transport, housing-related energy efficiency, lowering consumption of animal products, and low-carbon electricity generation. [flag: the “health and health equity benefits” column for this table contained no text as rendered on the slide]

For transport specifically, active travel interventions (beyond increased physical activity and reduced emissions) are associated with (Ding et al 2024): improved traffic safety, better physical and mental health, better economic outcomes (e.g. productivity, sick leave), better transport outcomes (shorter travel times, improved access), reduced air pollution, and improved social connection and cohesion.

An editorial cartoon satirises climate scepticism by contrasting a sceptic’s fear of wasted effort (“what if it’s a big hoax and we create a better world for nothing?”) with the list of co-benefits climate action would deliver regardless: energy independence, preserved rainforests, sustainability, green jobs, liveable cities, renewables, clean water and air, and healthy children.

Health sector adaptation

Principles for adaptation in the health sector:

  • Mitigation is the best form of adaptation.
  • Health workforce training.
  • Health infrastructure investment.
  • Public health strengthening.
  • Prevention builds resilience.
  • Partnership: health equity-centred adaptation done in partnership with iwi and councils.

The South Dunedin community illustration is used as a case example, depicting community wellbeing across cultural, spiritual, economic, social, physical and mental domains in a coastal neighbourhood facing flooding risk. [flag: small text within the illustration not legible] The proposed New Dunedin Hospital is presented as an example of “climate smart” health infrastructure planning, involving the Ministry of Health and the Southern District Health Board.

Climate leadership examples

A series of NZ clinicians, students and academics are presented as role models for climate and health action:

  • Dr Matt Jenks (anaesthetist, OraTaiao — NZ Climate & Health Council) is shown alongside a photo of an industrial chimney/incinerator stack. [flag: the slide does not state the relationship between the two photos; it likely illustrates hospital-related emissions or incineration, but this is not confirmed by slide text]
  • Jono Drew (medical student): research on healthy and climate-friendly diets (Drew et al 2020) estimates $13-20 billion in health savings over the life of the current adult NZ cohort. Modelled diets show progressively lower climate impact (kgCO2e/day) as they shift toward plant-based patterns: from the current NZ diet (~6.6) through dietary-guideline and substitution scenarios down to a waste-free vegan diet (~4.3), with savings attributed to reduced food waste, dietary change, and meeting dietary guidelines. [flag: precise bar-segment values not legible]
  • Dr Rebecca Randerson (GP): “Greening General Practice” initiative (ESHCA).
  • A/Prof Rhys Jones (Ngāti Kahungunu, public health physician): an Indigenous climate justice policy analysis tool using 13 criteria across 5 domains — relational justice, procedural justice, distributive justice, recognition/epistemic justice, and restorative justice.
  • Prof Anna Ranta (neurologist): the World Stroke Organization’s 2026 scientific statement on stroke and climate change, based on 189 publications reviewed by an international panel. Exposures considered: temperature, humidity/air pressure, wildfires, dust/sand storms, and compound weather events. Key recommendations: reduce emissions to protect and improve brain health, strengthen clinical and system preparedness, enhance early warning and response, promote equity and global coordination, and advance research. All exposures examined had some evidence of association with stroke incidence and/or mortality, but more high-quality studies are needed to establish causality, pathophysiological mechanisms, and adaptation strategies.
  • Dermot Coffey (GP, immediate past OraTaiao co-convenor): the “Climate Change and Health — Health Professionals Joint Call for Action” (Kotcher et al 2021), endorsed by a wide range of NZ and Australasian professional bodies including NZMA, NZ Nurses Organisation, NZ College of Public Health Medicine, Public Health Association, Royal Australasian College of Surgeons, Royal Australasian College of Physicians, Te ORA, ACEM, NZ Society of Anaesthetists, College of Nurses Aotearoa, NZ College of Midwives, NZMSA and AUMSA. [flag: several logos/organisation names on this slide were too small to read fully]

What medical students can do

  • Individual behaviour change.
  • Working with patients: taking a behaviour/environment (BE) history, providing climate education, prescribing healthy treatments.
  • Joining organisations: MSGA, OraTaiao, ESHCA, Sustainable Healthcare Aotearoa.
  • Research.
  • Engaging with community organisations.
  • Health sector change: both mitigation and adaptation.
  • Communication and leadership.
  • Active democracy.

Self-test

  1. Describe the planetary boundaries framework and explain how the number of boundaries assessed and crossed has changed from 2009 to 2025.
  2. Distinguish the “social foundation” from the “ecological ceiling” in the doughnut economics model, and give three examples of what sits inside each.
  3. List the “six truths about climate change” and explain what they are used to predict.
  4. Explain why the 2014 BMJ editorial framed climate change as a health emergency, and what kind of action it called for.
  5. Describe the four central climate drivers in the climate-health impact diagram and give one health effect linked to each.
  6. Explain the pattern of global injustice shown in the Lancet Countdown heat-mortality data: which regions show the largest increases, and how does this relate to who caused climate change?
  7. Describe the net effect on food-production-related deaths shown by Springmann et al 2016, including which dietary factors act to increase and decrease the total.
  8. Distinguish the two IPCC 1.5°C emissions pathways (net zero by 2040 vs 2055) in terms of their cumulative CO2 emissions.
  9. What did the Guardian article about COP29 report regarding fossil fuel lobbyist access, and why is this significant for climate policy?
  10. Compare NZ’s emissions profile to the world’s emissions profile by sector, noting the key structural difference.
  11. Describe the pattern of NZ’s gross and net greenhouse gas emissions from 1990 to 2024, and list two recent NZ policy changes cited as government inaction.
  12. List the four mitigation measures presented with health equity co-benefits, and describe the co-benefits identified for active transport specifically.
  13. List the six principles of health sector adaptation presented in the lecture.
  14. Describe the Indigenous climate justice policy analysis tool: its five domains.
  15. Summarise the key recommendations of the World Stroke Organization’s 2026 statement on stroke and climate change, and state what exposures it considered.
  16. A patient asks you what, as a medical student, you could realistically do about climate change. Using the lecture’s framework, describe three different types of action available to you.

Answers

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