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Cover Stories | June 2024

The Climate Crisis Is a Health Emergency

The effects on human and specifically ocular health.

In 2022, heat exposure killed at least five workers in Texas, including a landscaping worker who experienced severe heat stroke symptoms and later died in the hospital.1 Climate change was declared the biggest global health issue of the 21st century by The Lancet.2 Although we ophthalmologists specialize in eye health, it is important to emphasize that we are also committed to caring for our patients’ overall well-being. As such, it is critical that we understand how our rapidly changing environment is affecting human and planetary health. Extreme weather events, air pollution, rising sea levels and temperatures, and forced migration have an impact on all aspects of human health, including the eyes.

The Intergovernmental Panel on Climate Change unequivocally concluded that human activities, primarily through greenhouse gas emissions and land alteration from agriculture and deforestation, are the main drivers of global warming.3,4 As average global temperatures rise,5 heat waves and drought are becoming more frequent. The increasing loss of ice from Antarctica and Greenland is accelerating the rate of sea level rise.6 More intense rainfall is leading to flooding.7,8 Extreme weather events and rising carbon dioxide levels are precipitating environmental changes that are ultimately detrimental to human health. More than 9 million premature deaths worldwide are attributed to indoor and outdoor air pollution, which is both a cause and effect of climate change.


Climate change affects various health outcomes across a broad spectrum (Figure).9 A 2023 report from the Lancet Countdown emphasized that climate change is leading to irreversible human harm and endangering the survival of millions of people.10 Extreme heat is linked to heat stroke, arrhythmias, and cardiovascular failure. In 2019, high temperatures contributed to 93,000 cardiovascular deaths globally. In the United Kingdom, a study found that, for every 1 ºC increase in temperature above 23.2 ºC, there was a 1.5% rise in the risk of hospitalization for patients with chronic obstructive pulmonary disease.11 In 2020, 9-year-old Ella Adoo-Kissi-Debrah became the first person in the United Kingdom to have air pollution listed as a cause of death, following a severe asthma attack in 2013 due to unsafe levels of nitrogen dioxide in her area.12

Figure. This presentation from the Centers for Disease Control and Prevention highlights the primary effects and impact on health of climate change.9

Warming temperatures increase pollen production and virulence, prolong allergy seasons, and worsen air pollution, exacerbating respiratory conditions and causing more cases of allergic conjunctivitis.13,14 Studies have also shown an association between extreme heat exposure and a higher risk of emergency department visits related to kidney disease, including acute kidney injury, kidney stones, and urinary tract infections.15 For those who are pregnant, the impact of rising temperatures includes preterm birth, stillbirth, low fetal weight, and other complications.16,17

As the intensity of storms increases, ozone in the stratosphere decreases, allowing more UV radiation to reach people. Heat and increased UV exposure can exacerbate ocular and periocular conditions such as skin cancers, herpetic infections, and eczema as well as systemic lupus erythematosus.18

More frequent and intense droughts are leading to food insecurity, famine, and forced migration. Malnutrition may result in ocular diseases such as xerophthalmia due to vitamin A deficiency. Heat and drought are making wildfires more frequent and intense, thereby generating more chemically toxic smoke and increasing groundwater pollution.19 Heat-related changes in vector ecology are leading to a resurgence of previously eradicated diseases, such as dengue fever in the United States. Studies have suggested that higher temperatures linked to climate change can increase the incidence of trachoma infection. Additionally, climate change-induced factors such as migration, environmental degradation, and overcrowding, along with reduced sanitation, can hasten the spread of onchocerciasis.18,20

Environmental and climate changes are also affecting mental health. People directly harmed by climate change often develop posttraumatic stress disorder and depression, and there is a direct correlation between rising temperatures and interpersonal violence.21 A recent study has shed light on the profound concern among Generation Z regarding climate change, with greater than 80% of respondents feeling anxious about its impact.22

Climate change threatens everyone’s health but not equally. In the United States, the most severe harm disproportionately affects historically marginalized and underresourced communities who are least able to prepare for and recover from heat waves, poor air quality, and flooding.23 Other vulnerable groups include children, senior citizens, pregnant individuals, outdoor workers, individuals with chronic illnesses, and people living in island nations and developing countries.


Maintaining homeostasis is crucial for optimal eye function. The following material on the associations between climate change and ocular health has all been taken from original research articles cited in a recently published scoping review of the topic.24

Cornea, Conjunctiva, and Ocular Surface

Elevated temperatures and decreased humidity have been linked to a shorter tear breakup time, dry eye disease (DED), and a heightened risk of conjunctivitis, including acute hemorrhagic conjunctivitis and allergic conjunctivitis. Areas experiencing increases in rainfall and flooding are at growing risk of parasitic infections, such as microsporidia or Pythium keratitis, particularly during the monsoon season.

Exposure to sunlight or UV light increases the likelihood of developing pterygium and DED. Moreover, high ambient UV radiation exposure can reduce corneal resistance, increasing susceptibility to infection.

Airborne pollutants can increase the risks of conjunctivitis, conjunctivitis-related hospital visits, keratitis, and pterygium; the frequency of DED exacerbation, including DED related to Sjögren syndrome (due to its effect on chronic inflammatory pathways); and poor tear film quality.


Elevated temperature, UV radiation exposure, and airborne pollutants can hasten cataract development.

Refractive Error and Vision Impairment

Exposure to airborne pollutants can impair vision and cause myopia progression in children through oxidative stress and the reduced release of dopamine from retinal cells, which regulate axial growth. Although outdoor activities can slow myopia progression by providing higher solar illumination, the benefit may be mitigated in areas with high levels of air pollution and UV radiation.


Exposure to heat waves and cold spells—more common in our changing climate—has been found to raise the occurrence of both primary angle-closure glaucoma and primary open-angle glaucoma. Primary angle-closure attacks are more common during the monsoon season. The frequency of pseudoexfoliation syndrome has been associated with sun exposure and rising temperatures. Oxidative stress, neuroinflammation, and hypercoagulability induced by air pollutants contribute to retinal ganglion cell death and subsequent neuropathy. Other proposed mechanisms include damage to trabecular meshwork cells, leading to elevated IOP and the development of glaucoma.

Lids and Ocular Adnexa

Lower temperatures and exposure to airborne pollutants have been associated with meibomian gland dysfunction and blockage and blepharitis, which increases the risks of evaporative DED and keratitis.

In addition to the risk of periocular tumors associated with exposure to UV radiation, climate change seems to increase the risk of periocular and orbital infections. In Japan, increased temperatures have been linked to periocular fungal sporotrichosis infections. A rise in rhino-orbital mucormycosis cases occurred following a month of widespread flooding in the Denver-Boulder metropolitan area.

Retina and Ocular Inflammation

Elevated ambient temperature has been linked to higher rates of rhegmatogenous retinal detachment, possibly due to alterations in chorioretinal adhesion and vitreous liquefaction. Elevated temperatures and temperature variability may correlate with the risk of uveitis, particularly the noninfectious form. Greater rainfall has been linked to the reactivation of toxoplasma retinitis, particularly during the second and fourth quarters of the year, notably during the El Niño phenomenon.


Temperature fluctuations, exposure to UV radiation and airborne pollutants, and extreme weather events pose disproportionate yet significant threats to human health and biodiversity worldwide. The impact of climate change on general and ocular health demands comprehensive physician education (as declared by the American Medical Association)25 and action. Health care generates 8.5% of US greenhouse gas emissions.26 As physicians, we have a unique opportunity to reduce the carbon footprint of health care, call for policy change, educate our colleagues and community, and advocate for our patients.

1. Sainato M. ‘It’s become unbearable’: Texas workers toil through extreme heatwave. The Guardian. June 30, 2023. Accessed April 23, 2024. https://www.theguardian.com/us-news/2023/jun/30/texas-heatwave-worker-protections-illness-sun-exposure

2. Climate change crisis goes critical. The Lancet Respiratory Medicine. 2023;11(3):213.

3. California Institute of Technology. What is the evidence for human-caused climate change? 2024. Accessed March 20, 2023. https://scienceexchange.caltech.edu/topics/sustainability/evidence-climate-change

4. Herring D, Lindsey R. What evidence exists that Earth is warming and that humans are the main cause? NOAA. October 12, 2022. Accessed March 20, 2024. https://www.climate.gov/news-features/climate-qa/what-evidence-exists-earth-warming-and-humans-are-main-cause

5. Papalexiou SM, AghaKouchak A, Trenberth KE, Foufoula-Georgiou E. Global, regional, and megacity trends in the highest temperature of the year: diagnostics and evidence for accelerating trends. Earth’s Future. 2018;6(1):71-79.

6. The IMBIE team. Mass balance of the Antarctic ice sheet from 1992 to 2017. Nature. 2018;558(7709):219-222.

7. Borodina A, Fischer EM, Knutti R. Models are likely to underestimate increase in heavy rainfall in the extratropical regions with high rainfall intensity. Geophys Res Lett. 2017;44(14):7401-7409.

8. Emanuel K. Assessing the present and future probability of Hurricane Harvey’s rainfall. Proc Natl Acad Sci USA. 2017;114(48):12681-12684.

9. Centers for Disease Control and Prevention. Climate and Health. April 25, 2022. Accessed March 20, 2023. https://www.cdc.gov/climateandhealth/

10. Romanello M, Napoli CD, Green C, et al. The 2023 report of the Lancet Countdown on health and climate change: the imperative for a health-centered response in a world facing irreversible harms. Lancet. 2023;402(10419):2346-2394.

11. Konstantinoudis G, Minelli C, Vicedo-Cabrera AM, Ballester J, Gasparrini A, Blangiardo M. Ambient heat exposure and COPD hospitalisations in England: a nationwide case-crossover study during 2007–2018. Thorax. 2022;77(11):1098.

12. BBC News. Ella Adoo-Kissi-Debrah: air pollution a factor in girl’s death, inquest finds. 2020. Accessed February 24, 2024. https://www.bbc.co.uk/news/uk-england-london-55330945

13. Hong J, Zhong T, Li H, et al. Ambient air pollution, weather changes, and outpatient visits for allergic conjunctivitis: a retrospective registry study. Sci Rep. 2016;6(1):23858.

14. Das AV, Basu S. Environmental and air pollution factors affecting allergic eye disease in children and adolescents in India. Int J Environ Res Public Health. 2021;18(11):5611.

15. Qu Y, Zhang W, Boutelle AYM, et al. Associations between ambient extreme heat exposure and emergency department visits related to kidney disease. Am J Kidney Dis. 2023;81(5):507-516.e1.

16. Rylander C, Odland JØ, Sandanger TM. Climate change and the potential effects on maternal and pregnancy outcomes: an assessment of the most vulnerable—the mother, fetus, and newborn child. Glob Health Action. 2013;6:19538.

17. Ghazi T, Naidoo P, Naidoo RN, Chuturgoon AA. Prenatal air pollution exposure and placental DNA methylation changes: implications on fetal development and future disease susceptibility. Cells. 2021;10(11):3025.

18. Anderson JG, Wilmouth DM, Smith JB, Sayres DS. UV dosage levels in summer: increased risk of ozone loss from convectively injected water vapor. Science. 2012;337(6096):835-839.

19. Environmental Protection Agency. Wildfires: How do they affect our water supplies? August 13, 2019. Accessed March 20, 2024. https://www.epa.gov/sciencematters/wildfires-how-do-they-affect-our-water-supplies

20. Tidman R, Abela-Ridder B, de Castañeda RR. The impact of climate change on neglected tropical diseases: a systematic review. Trans R Soc Trop Med Hyg. 2021;115(2):147-168.

21. Mahendran R, Xu R, Li S, Guo Y. Interpersonal violence associated with hot weather. Lancet Planet Health. 2021;5(9):e571-e572.

22. Salguero RB, Bogueva D, Marinova D. Australia’s university Generation Z and its concerns about climate change. Sustain Earth Reviews. 2024;7(1):8.

23. Environmental Protection Agency. Social Vulnerability Report. April 24, 2023. Accessed March 20, 2024. https://www.epa.gov/cira/social-vulnerability-report

24. Wong YL, Wong SW, Ting DSJ, et al. Impacts of climate change on ocular health: a scoping review. J Clim Change Health. 2024;15:100296.

25. AMA. Climate Change Education Across the Medical Education Continuum H-135.919. 2019. Accessed March 24, 2024. https://policysearch.ama-assn.org/policyfinder/detail/climate%20change?uri=%2FAMADoc%2FHOD.xml-H-135.919.xml

26. The White House. FACT SHEET: Health Sector Leaders Join Biden Administration’s Pledge to Reduce Greenhouse Gas Emissions 50% by 2030. The White House. June 30, 2022. Accessed April 29, 2024. https://www.whitehouse.gov/briefing-room/statements-releases/2022/06/30/fact-sheet-health-sector-leaders-join-biden-administrations-pledge-to-reduce-greenhouse-gas-emissions-50-by-2030/

Barbara C. Erny, MD
  • Adjunct Clinical Associate Professor, Stanford University School of Medicine, Stanford, California
  • barbaraernymd@gmail.com
  • Financial disclosure: None
Yee Ling Wong, MBChB
  • Ophthalmology resident, Manchester Royal Eye Hospital, Manchester, United Kingdom
  • yeelingwong@nhs.net
  • Financial disclosure: None
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