Climate, Health, Humanity: Rethinking Our Balance after the 2025 Lancet Countdown Report and the Gates Memo

On Wednesday 29 October, the latest edition of the Lancet Countdown, published in collaboration with the World Health Organization (WHO), once again delivered an alarming assessment: twelve of the twenty indicators monitoring climate-related health threats have reached record levels. This finding illustrates the growing human cost of climate inaction. Human, animal, and environmental health are closely interdependent – the very essence of the One Health concept, born in the early 2000s – and responses to the environmental crisis must be grounded in this logic of intersectionality between risks and pathogens.

Is climate change still an environmental crisis, or has it already become a disruption of life itself?

Climate change is no longer merely a matter of degrees: it now manifests in bodies, minds, and health systems. The Lancet Countdown 2025 marks a turning point, not because it reveals a link long established, but because it measures it in all its transversality. Heatwaves, wildfires, droughts, and vector-borne diseases are no longer parallel crises; they form a continuum of biological, social, and psychological disruptions that make climate a central determinant of global health.

Heat-related mortality has risen by around 63% since the 1990s, reaching nearly 550,000 deaths per year over the past decade. Productivity losses due to heat stress account for roughly 1% of global GDP – over one trillion dollars annually. Meanwhile, fires cause tens of thousands of deaths each year from fine-particle pollution, dengue-carrying mosquitoes are spreading into once-temperate latitudes, and 124 million more people fell into food insecurity in 2023. These figures are no longer projections; they describe a world already physiologically destabilised. This is not just climate disruption – it is the disruption of life itself.

It disorganises biological rhythms and vital infrastructures. Air, water, soils, species, ecosystems – even our own bodies – all respond as a single system out of balance. Rising temperatures affect sleep, fertility, mental health, cardio-respiratory function, concentration, and social cohesion. This diagnosis echoes the planetary boundaries framework: crossing the climate threshold weakens all others – biodiversity, water cycles, soils, pollutants, nitrogen, phosphorus – thereby undermining the very conditions of survival.

It is in this sense that I propose the concept of a “health boundary”: not a tenth biophysical limit, but a transversal indicator of the Earth system’s stability. Human health becomes the compass measuring, in real time, the compatibility between our lifestyles and planetary equilibria. When heat-related mortality, post-disaster psychiatric disorders, or productivity losses reach such levels, they signal not just a medical crisis but that the whole of life – human and non-human – is leaving its zone of stability.

The Lancet Countdown 2025 therefore goes beyond description: it calls for a shift in scale. Far from opposing planet and humanity, it invites us to view health as an integrated measure of our interdependence. Saving the planet is no longer an abstract ideal; it means preserving the physiological and psychological conditions for a stable human life within collapsing natural equilibria. Climate is no longer merely an environmental variable: it has become a vital indicator.

Can adaptation truly save humanity in a world where limits have already been crossed?

On the very day the Lancet Countdown 2025 was released, Bill Gates published a memo striking a different tone. He describes climate change as a major, but not existential, challenge: humanity, he writes, will continue to “live and thrive” across most of the planet. The issue, he argues, is not survival but the equitable distribution of well-being.

His reasoning follows a logic of efficiency: as global resources are limited, they should be directed where they most improve human life. Rather than pursuing an abstract climate target, he proposes investing in levers that directly strengthen the resilience of the most vulnerable – vaccination, nutrition, climate-resilient agriculture, accessible energy. This approach usefully situates climate action within the broader field of human development and global health.

Yet this vision, grounded in adaptive capacity, rests on debatable assumptions. It presumes that societies can always adjust to changing environments, whereas some regions have already reached their biophysical limits. In the Persian Gulf, India, or the Horn of Africa, heatwaves exceeding 35°C of wet-bulb temperature directly threaten human viability without air conditioning or migration.

It also tends to downplay the scale of irreversible losses and damages. The UN Environment Programme’s Adaptation Gap Report 2023 estimates that the adaptation finance gap in developing countries lies between $194 and $366 billion annually, excluding unquantifiable health, cultural, and ecological losses. These figures remind us that adaptation, far from being limitless, carries costs and physical constraints.

Finally, this techno-centred approach – privileging market-driven innovation – raises questions of climate justice. Private investment tends to focus on patentable solutions – seeds, technologies, infrastructures – accessible only to solvent nations. Adaptation thus becomes both a measure of power and a matter of survival.

The Lancet Countdown adopts a complementary but more systemic perspective: it shows that health is not confined to individual resilience but to the stability of ecological and social equilibria.

These two visions are therefore not wholly opposed. They reflect two hierarchies of values: one believes in humanity’s capacity to innovate in a warmer world; the other reminds us that without recognised physical and social limits, innovation risks deepening the inequalities it claims to solve.

What if health became the new measure of climate?

Between the health warning of the Lancet Countdown 2025 and the pragmatism of the Gates memo, one fact stands out: health must become the integrated measure of climate. But to achieve this, the world must rethink the way it governs this crisis.

First requirement: broaden the indicators

Climate action continues to be assessed through physical metrics – tonnes of CO₂ avoided, degrees contained, shares of renewable energy. These remain essential, but they capture only part of reality: that of energy flows and balances.

To grasp the real-world effects of disruption, they must be paired with human indicators: mortality avoided, working days preserved, agricultural yields maintained, air quality, mental health, life expectancy. This biological translation of climate allows us to identify the “pathogenic” side effects of purely technological solutions that cut carbon but worsen other imbalances – deforestation for biofuels, unregulated mining, etc. Moving from a carbon balance to a human balance is to acknowledge the transversality of our equilibria.

Second requirement: embed health at the heart of mitigation and adaptation policies, in a One Health logic

The issue is not merely to add health goals to climate policies, but to design policies whose very purpose explicitly connects human health, animal health, and ecosystem integrity. This is the essence of One Health: preventing health crises by addressing environmental and social causes before they become irreversible.

In practice, vaccination strategies, anti-malnutrition policies, agri-food reform, or expanded access to clean energy are not mere side co-benefits of climate policy. They are instruments of adaptation and primary prevention. They reduce exposure to heatwaves, limit zoonoses and vector-borne diseases, stabilise yields without deforestation, improve air quality and respiratory health, and strengthen the resilience of health systems.

This approach also requires integrating risks still largely absent from traditional climate plans: antimicrobial resistance exacerbated by environmental stress and intensive livestock practices, or interspecies transmission linked to deforestation and land-use change. It also calls for genuinely cross-sectoral governance – health, agriculture, environment, economy – and for independent evaluation mechanisms to prevent “pathogenic solutions” that merely shift risks without resolving them.

Nonetheless, the current limits of One Health must be acknowledged: causal chains between climatic variables, diseases, and ecosystems remain complex, veterinary and environmental data are incomplete, and benefits often unfold over longer horizons than political or budgetary cycles. Hence the need for stable, long-term scientific stewardship.

Third requirement: rebuild global financial governance

According to the Lancet Countdown 2025, fossil fuel subsidies reached nearly $956 billion in 2023 – more than the total global public health budget. When factoring in the hidden costs these energies impose on society – air pollution, disease, premature mortality, untaxed emissions – the International Monetary Fund estimates that the overall implicit support to fossil fuels exceeds $7 trillion annually. This imbalance highlights the persistence of an economy still built on energy rent rather than systemic risk prevention.

Development aid must therefore be reimagined, not as “green charity”, but as the co-production of planetary stability. Climate finance should reflect the real cost of loss and damage, include debt cancellation or restructuring for vulnerable countries, and value the health co-benefits of mitigation policies.

Under Brazil’s G20 presidency in 2024, and on the eve of hosting COP30 in Belém in 2025, Brazil stands at the centre of global climate diplomacy.

As both a megadiverse country – home to an exceptional share of global biodiversity – and one marked by deep social inequality, Brazil embodies the tension between ecological urgency and development needs. President Lula has made the fight against hunger, a just energy transition, and reform of global governance the central pillars of his diplomacy, seeking to position Brazil as a mediator between the expectations of the South and the commitments of the North.

If health becomes the shared language of this governance – the language of life rather than of economic flows alone – then international cooperation can finally move beyond the logic of compensation toward that of shared human capabilities.