The health impact of climate change

GVS Murthy

What is climate change?
Climate change can be our biggest challenge in the post COVID era. Climate change is nothing but climate variability which has become more intense in the recent past. Thus, we are seeing longer monsoons, more intense rainfall, more days of summer with temperature highs and increased relative humidity.

Global warming has been the overriding concern for the past few decades. Human lifestyle is thought to have increased the quantity of heat-trapping gases which are responsible for the greenhouse effect, particularly carbon dioxide which makes up 60% of this effect. Several types of gases can reflect or trap heat, including carbon dioxide (CO₂), methane, nitrous oxide, water vapour, halocarbons, and ozone. Particulate material such as sulphur dioxide and dust reflects solar irradiation, while other particles such as black carbon retain heat.

Extreme weather events are already being experienced in India, and this both directly and indirectly affects the health of the population.

The average annual temperatures in India in 2030, compared to the 1970s, are projected to increase between 1.7 and 2.2° Celsius. According to a recent Lancet report*, the frequency of weather-related disasters between 2007 and 2016 increased by 46% (globally). Four regions in India are at a higher risk of climate change impact – Himalayan and sub-Himalayan regions, the Northeastern hills and plains, Western Ghats, and coastal India.

Unanticipated climatic events, such as extreme heat waves, temperatures, shrinking glaciers, forest fires, droughts, and floods are putting human health at risk.

How does climate change affect health?
As with many other walks of life, climate change has an adverse impact on health as new infectious agents take a foothold in our environment due to increased air pollution and heat stress and forgotten arthropods become more menacing along with increased migration and displacement due to events like floods and cyclones which are now occurring with increased frequency. Meteorological changes also impact disease carrying vectors, agriculture and food supplies and therefore decrease food security as well. Thus, weather has a direct impact on our health.

Excessive heat and prolonged exposure to high temperatures, especially in areas not accustomed to too much heat, can lead to diseases and deaths. Higher temperatures affect the concentration of air pollutants and allergen aerosols like pollen. Allergenic pollens grow significantly in warmer climates and lead to respiratory problems like asthma and bronchitis. Air quality decreases as surface ozone concentrations rise due to higher environmental temperatures. This in turn leads to increased respiratory problems like asthma and problems of the cardio vascular system. Similarly floods contaminate drinking water supplies, which expedite transmission of diarrhoeal diseases and cholera.

The stratospheric ozone depletion with the potential increase in solar UV radiation has emerged as one of the most important effects of global change. This is particularly significant for the northeastern region of the country where the anthropogenic tropospheric ozone and aerosols have not masked the effect of ozone depletion on UV-B radiation to a large extent. The stratospheric ozone depletion that is leading to increased UVR in the biosphere has several health hazards.

Increased temperatures and humidity are ideal for the growth of vectors like mosquitoes that cause devastating diseases. The extent of the country that is affected by vector-borne diseases like malaria, dengue, Japanese encephalitis will increase due to increased rainfall and temperatures in locations like the hilly regions. Studies undertaken in India reveal that the transmission window during which malaria occurs in states of northern and north eastern India can extend by 2-3 months while in southern and eastern states like Odisha, Andhra Pradesh, and Tamil Nadu this transmission window may reduce. The incidence of Japanese encephalitis has been reported to be increasing over the past 5-10 years in eastern Uttar Pradesh.

Similarly, the occurrence of diseases like malaria in the upper reaches of the Himalayas in the last decade can be attributed to climate change as can be the appearance of kala-azar or black fever, which was predominantly seen in Bihar, but is now being reported from Himachal Pradesh and reappearing in Assam.

The risk of severe outbreaks of vector-borne diseases will increase, because viruses multiply more rapidly in vectors like mosquitoes and also because vectors like mosquitoes grow at a rapid pace in high temperatures. This leads to shorter incubation period for diseases like malaria and dengue and therefore there is a likelihood of an explosive outbreak.

The young and the aged will be most at risk of the impact of climate change, as will those with chronic conditions like respiratory and heart ailments, increased blood pressure or diabetes as such people have compromised coping mechanisms.

Thus, climate change has the potential to undo the vast gains that public health and modern medicine have given us over the past 40-50 years.

How can the health impact of climate change be classified?
The health impact of climate change can be categorized into direct health impact and indirect health impact.

Direct health impact
Direct health impact of climate change can be due to:
• Physical effect: Heat stress, heat exhaustion, bodily harm (floods, cyclones), etc. Flooding poses health risks due to trauma, drowning, and exposure to pathogens and toxic compounds in contaminated waters. Also electrocution can lead to death and disability.
• Entomological effect: Faster multiplication of vectors and micro-organisms. The geographic span and density of disease vectors is changing, exposing more people to tick borne and mosquito-borne illnesses.
• Biological effect: Prolonged exposure to high temperatures can cause adverse pregnancy outcomes including still births, premature births, and congenital birth defects.
• Chemical effect: Increasing atmospheric CO₂ and changes in precipitation factors affect air quality which negatively impacts heart and respiratory health. Physiologically, ozone and PM_2.5 cause inflammation of the respiratory tract and endothelial cell dysfunction and oxidative injury aggravating cardiopulmonary disease and contributing to premature death. In India, the mean PM_2.5 increased from 60 μg/m3 in 1990 to 76 μg/m3 in 2015, accompanied by an increase in mean ambient ozone exposure from 62 to 76 ppb.

Indirect health impact
Indirect health impacts cannot be easily attributed to climate change, but there is evidence to show that adverse climatic conditions ultimately impact human health.
• Food Security: In countries like India, malnutrition rates are already high and this is projected to increase significantly as agriculture production is adversely affected by climate change. This will be a concern for the Sustainable Development Goal of Zero Hunger by 2030. Available evidence shows that children from districts with high climate change vulnerability showed higher rates of malnutrition.
• Plant and animal health: Plant and animal disease in turn can lead to adverse human health. The alteration of habitats brings plants, animals, and humans in close contact, which can trigger a spillover of infection from one kingdom to another. COVID-19 is a classic example of how the animal-human interface can have disastrous consequences if adequate surveillance mechanisms are not in place. Therefore, One Health concept has to be pursued vigorously to reduce the risk of health consequences due to climate change. One Health strengthens collaborations at all levels among professionals working for plant, animal, and human health so as to achieve optimum health outcomes for all in the shared environment.

Body parts and organs affected by climate change
All organs in the body and all physiological systems are adversely impacted by climate change. This is not to say that climate change causes these health conditions but what it means is that climate change increases the risk of these health conditions or increases the speed at which they occur.

Eyes: Climate change affects the eyes mainly due to depletion of the ozone layer. Roughly, a 1% decrease in the ozone layer will cause an estimated 2% increase in UV-B irradiation. Studies have reported a higher prevalence of cataract in regions that have unusually high levels of UV exposure. Various ocular disorders induced and exacerbated by UVR include cataract, dry eye, pterygium, allergic diseases, photokeratitis, ocular surface cancers, corneal degenerative changes and age-related macular degeneration.

UV-A is not absorbed by the ozone and reaches the Earth’s surface without being filtered out through the clear atmosphere (ozone depleted atmosphere). UV-B radiation, being more energetic is also more damaging to the eye and is absorbed by the cornea and lens. UV-A radiation has lower energy, but penetrates deeper into the eye and may cause injury to the retina.

Thermo regulation and skin: Heat stress could result in heat cramps, heat exhaustion, heat stroke and damage physiological functions, metabolic processes and immune systems. Heat stress occurs when the body is unable to control the internal temperature mechanisms. Exposure to UV-B increases the risk of skin cancers.

Respiratory system: Increasing incidence of respiratory diseases like bronchitis, emphysema, allergic rhinitis, asthma, chronic obstructive airway disease, etc., have been reported due to climate change.

Cardiac system: Increased rates of hypertension, cardiac arrests and premature deaths have been projected to occur with climate change.

Gastro intestinal system: Increased diarrhoea, typhoid, and cholera in areas which are affected by climate change wrought catastrophes like floods, cyclones and tsunamis.

With increasing antimicrobial resistance, any increased risk of infections of any human system is fraught with the risk of increased mortality and disability.

Multi system disorders: Zika virus, dengue, chikungunya, typhoid and malaria affect many organs of the body and enhanced vector transmission and survival due to climate change can increase the number of cases and expansion of the geographic areas where these infections are seen currently.

Are countries like India more at risk of climate impact?
The major impact of global climate change will be on low and middle income countries, where the magnitude of climate-sensitive diseases which cause more sickness and death like malaria, diarrhoea, heat stress and exhaustion, and respiratory and cardiac conditions is already high. This coupled with a lack of adequate health service machinery is going to be a major challenge for countries like India. In India, 70% of the population resides in rural habitations where access to modern diagnostic and treatment facilities is poor and access to quality health care in urban areas is not easy.

Low and middle income countries are responsible for a small proportion of greenhouse gas emissions, but they are liable to shoulder a disproportionate burden of the adverse health effects of climate change.

Within these countries, women and children suffer more from climate change compared to men. Studies have shown that older and pregnant women, suffer a greater burden of heat related adverse effects.

The prime minister’s National Action Plan on Climate Change in India
To mitigate the adverse impact of climate change, a high powered group has been constituted by the prime minister to suggest steps for surmounting the health challenge. These steps include:
• Provision of enhanced public health care services.
• Assessment of increased burden of diseases due to climate change.
• Providing high-resolution weather and climate data to study the regional pattern of diseases.
• Development of a high-resolution health impact model at the state level.
• GIS mapping of access routes to health facilities in areas prone to climatic extremes.
• Prioritization of geographic areas based on epidemiological data and the extent of vulnerability to adverse impacts of climate change.
• Study of air pollutants and pollen (as the triggers of asthma and respiratory diseases) and how they are affected by climate change.
• Studies on the response of disease vectors to climate change.
• Enhanced provision of primary, secondary and tertiary health care facilities and implementation of public health measures, including vector control, sanitation, and clean drinking water supply.

To confront the health challenges of climate change, in addition to the action at the government level, there is urgent need for individual and civil society response. Reduced use of individual vehicles and replacement of environmental hazards, increased awareness at the community level and community participation to share responsibilities is important if some of the adverse effects are to be reversed.

*https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)32464-9/fulltext

The author is the Director, Indian Institute of Public Health, Hyderabad. He can be reached at murthy.gvs@iiphh.org.