According to the World Health Organisation, 24% of global mortality can be attributed to environmental issues, (1) which exposes a biological truth humanity can no longer ignore: Homo sapiens, for all its technological prowess, remains inextricably embedded within Earth’s life-support systems. The emerging paradigm of planetary health, defined as “the health of human civilization and the state of the natural systems on which it depends” (2), reveals this fundamental interdependence, and demonstrates how anthropogenic degradation of atmospheric, aquatic, and terrestrial systems manifests pathologically in human bodies. In other words, if the planet is sick, so are we. This essay examines four pathological pathways linking planetary and human health: climatic destabilization, biodiversity collapse, toxic pollution bioaccumulation, and psychological distress induced by ecological breakdown.

Atmospheric CO₂ concentrations now exceed 420 ppm, driven by annual emissions surpassing 40 billion metric tons (3) . Carbon dioxide exerts strong climate impacts due to its molecular properties, with strong polar bonds and multiple vibrational modes enabling exceptional infrared photon absorption, and enhancing radiative forcing. These characteristics drive the observed rise in global mean temperatures. Rising global temperatures are increasing the incidence of life-threatening heat-related illnesses. Heat stroke represents one of the most severe manifestations. It is characterised by a core body temperature exceeding 40°C, and is often accompanied by neurological dysfunction (4) The World Health Organization documents approximately 489,000 annual heat-related deaths globally (5) , a mortality burden projected to grow substantially as climate change intensifies. The health consequences also extend beyond direct heat effects. Epidemiologist Dr. Katie Anders, director of the World Mosquito Program, warned that climate-driven weather extremes create new mosquito breeding habitats. (6) This phenomenon dramatically increases the risk of vector-borne disease outbreaks, and is evident in the expanding ranges of the virus-carrying Aedes Aegypti mosquito. (7) This proves that there is a direct correlation between the rising temperatures of our increasingly “feverish” planet, and the health and welfare of human beings.

Another manifestation of our planet’s “sickness” is a severe loss of biodiversity. Pollinators in the UK have already experienced a 24% decline in population, and have become 42% less widespread. (8) Over 1200 crops worldwide rely on pollination to thrive, (9) meaning that a persistent decline in pollinators due to our degrading environment could lead to food scarcity, and in the worst cases famine. These consequences would be detrimental to global health, as many will experience starvation, or fall victim to microorganisms, which are prevalent in weakened unpollinated plants. (10) The destruction of ecosystems and habitats inevitably forces animals into urban areas. (11) This interface increases human-animal contact, and drives zoonotic disease transmission, accounting for 60% of current emerging diseases. (12) Outbreaks can bring heavy destruction as seen with the 2020 COVID-19 pandemic, which saw animal to human transmissions of coronaviruses originating from bats. (13) These examples demonstrate that the destruction of our planet’s natural systems can lead to negative repercussions in human health.

Anthropogenic impacts on planetary health can also have a profound impact on our own bodies. In 62 samples of human placentas, microplastics were detected, with concentrations ranging from 6.5-790 μg/g. (14) These particles infiltrate biological systems through industrial runoff-polluted water supplies, contaminating drinking water. (15) At the cellular level, microplastics increase free radical counts by triggering cells to produce more reactive oxygen species (ROS), (16) leading to oxidative stress, which damages DNA and increases cancer risk. Similarly, synthetic polymers like polybrominated diphenyl ethers (PBDE), commonly used in flame retardants pervasive in household products, have serious side effects. PBDEs bioaccumulate through contaminated soils and crops. A longitudinal study conducted by the University of California with 3,000 mother-child pairs, discovered “that every 10-fold increase in a mom’s PBDE levels led to a drop of 3.7 IQ points in her child”. (17) PBDEs’ high lipophilicity enables adipose tissue sequestration, with placental and breastmilk transfer rates, demonstrating the intergenerational neurotoxicity of these pollutants. Moreover, industrial activities release heavy metals which eventually get released into the ocean, and are consumed by sea creatures and converted into methylmercury. (18) When humans ingest fish, 95% of organic mercury is absorbed into the blood, (19) combining with haemoglobin in blood and building up in the central nervous system. (20) In many cases, this buildup can lead to cognitive and motor dysfunction with high concentrations. Additionally, prenatal exposure to just 1 ppm can cause permanent developmental delays. (22)

The causal link between planetary and human health is starkly evident in the respiratory ravages of air pollution. Emissions from industrial activities and vehicles not only make our planet fall ill, but release harmful PM2.5 fine particulates into the air. These substances can evade the mucociliary system in the respiratory tract (23), reaching deep into the lungs and damaging the walls of alveoli. (24) More critically, polycyclic aromatic hydrocarbons are commonly found attached to PM2.5, formed during incomplete combustion or pyrolysis. (25) As a result of metabolism, they can form highly carcinogenic DNA-adducting intermediates, giving rise to oncogene mutations that greatly increase the likelihood of cancer. (26) Moreover, fossil fuel combustion releases NO2 and other highly reactive pollutants which can irritate airways and induce the onset of asthma in young children, especially with prolonged exposure. (27) “Biochemical assault” is especially experienced by those in the vicinity of oil refineries, as they inhale high levels of SO2, and O3 as a result of reactions with NOx radicals. (28)(29) Exposure to these two gases cause COPD, a respiratory disease that causes inflammation and destroys air sacs. (30)

While physical health effects are grave, psychological impacts are equally systemic, conveyed in recent neuroepidemiological studies. The psychological toll of planetary degradation represents a silent epidemic, as environmental breakdown rewires our mental health and society. In a study involving US and UK participants, results showed that people from both nations had symptoms of anticipatory solastalgia (31) , a human distress syndrome corresponding with increasing ecosystem distress. (32) A 2021 study conducted with 2039 participants, discovered a correlation between higher levels of NOx and PM2.5 exposure and the development of depression (MDD). (33) Prenatal exposure to PM2.5, especially in the first trimester of pregnancy, correlates with higher rates of adolescent depression as well. (34) Even indirect pathways, such as climate-driven food insecurity, elevate interpersonal violence, and innate aggression. Children growing up with malnourishment due to climate crises showed a higher likelihood of developing psychopathic tendencies later on in their lives. (35) This data reveals that planetary sickness does not merely surround us, but permeates the human mind, eroding every facet of human health.

Collectively, these case studies evidence a dose-response relationship between ecosystem disruption and human morbidity. From PM2.5-induced illnesses to neurotoxic methylmercury bioaccumulation, ecosystem impairment manifests clinically across physiological and psychological domains. Just as Hippocratic medicine recognizes that treating fever requires addressing its underlying infection (36) , governments must target the root pathologies of ecological breakdown to strive towards better global health. Dr. Margaret Chan, Former Executive Director of the World Health Organisation, emphasised that “a ruined planet cannot sustain human lives in good health. A healthy planet and healthy people are two sides of the same coin.” (37)


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