Global Warming and Health

Introduction

Global warming is occurring at an alarming rate due to the combustion of fossil fuels, including coal, petroleum, and natural gas. It is associated with anthropogenic emissions of greenhouse gases, airborne particulates, nitrogen, and sulfur dioxide. John Tyndall had visualized in 1861, that anthropogenic carbon dioxide emission would trap the radiant energy of the Sun within the atmosphere of the earth and raise the surface temperature.¹

Health Impact

Global warming has health impacts and has emerged as a public health challenge.² ‘Protecting health from climate change’ focuses on the adverse effects on health posed by global climate variability and change. There is a threat to international public health from extreme weather-related disasters to the wider spread of vector borne diseases.

The Montreal Protocol of 1987 gave new directions in protecting the planet by phasing out chlorofluorocarbons (CFCs) and related compounds that were causing the depletion of UV-absorbing ozone.³

Human activities are associated with deforestation and the burning of fossil fuels. They cause a change in the concentration of atmospheric constituents or properties of the earth's surface that facilitate absorption or scattering of radiant energy.⁴ There is a marked increase in the production of anthropogenic greenhouse gases such as carbon dioxide, methane, and nitrous oxide that have made the air warmer. There is the emission of noxious particles and pollutant gases such as sulfur dioxide, carbon monoxide, and nitrous oxides. Higher atmospheric temperatures cause rapid water evaporation of surface water, increasing humidity, and higher levels of precipitation, resulting in heat waves, hurricanes, floods, and droughts and their attendant physical effects.⁴ There is a corresponding increase in the number of victims and their injuries, hospitalizations, and financial losses.⁵

Surface Temperature

During the past hundred years (from 1906 to 2005), the global average surface temperature has risen by 0.75°C, and the global sea level has risen on average by approximately 2 mm per year. The concentration of carbon dioxide (CO₂ ), the chief cause of the greenhouse effect, has risen from 280 parts per million (ppm) to 360 ppm since the beginning of the industrial revolution, mostly due to the burning of fossil fuels. The rate of climate change has increased in recent times more than in any period in the last millennium.⁶

The United Nations Intergovernmental Panel on Climate Change (IPCC) established by the United Nations Environmental Programme (UNEP) and the World Meteorological Organization (WMO) has predicted that if current trends continue, sea level will rise between 18 and 59 cm and global temperature will increase between 1.8 and 4.0 °C  by the end of this century. The unhindered use of fossil fuel in the future is likely to increase the concentration of CO₂ by 2100 and it will be in the range from 540 ppm to 970 ppm. The decrease in snow cover, the melting of the polar ice caps, the receding glaciers, and the thermal expansion of seawater have already resulted in a detectable rise in sea level. It has serious implications for the health of coastal people. It puts the town and city areas under water, makes the sewage systems inoperable, salinates the rice growing areas, and affects hygiene and health.

Any small alteration in global temperatures can cause relatively large changes in the frequency of extreme temperatures. High temperatures are associated with increased deaths of elderly and persons with preexisting diseases. Heat waves causing higher average ambient air temperatures not only increase mortality from cardiovascular, cerebrovascular, and respiratory diseases but also cause air pollution.

Extreme temperature causes physical injury. There is poor nutritional status and an increased incidence of respiratory and diarrhoeal diseases due to overcrowding, disruption of water supplies, and the sewage system. Increasing the evaporation of water from the oceans will increase the probability of floods. The immediate effects of flooding are an increase in the number of injuries and drownings. The medium-term effects are an acute shortage of clean drinking water, and infection from contaminated water often leads to an increased incidence of cholera and hepatitis A. In the long term, the destruction of croplands by salination and the wiping out of harvests results in undernutrition.

El Nino

The El Nino event caused the shift of warm equatorial water from the western to the eastern Pacific Ocean. This occurs periodically every 3 to 7 years, leading to extremely dry conditions, droughts, and devastating f ires in many regions of the world and torrential rains and flooding in other regions.⁷ There is an increased incidence of communicable diseases such as cholera and hepatitis A due to the drinking of contaminated water, leptospirosis due to contact with contaminated water from rodent excreta, respiratory infections due to the overcrowding of flood survivors, or mold overgrowth in f looded houses.⁴

Global climate change brings about changes in the hydrological cycle (floods and droughts). Droughts affect food production. Its consequences are mostly indirect, leading to poor nutritional status, starvation, and undernourishment. Water is scarce, and very little is left over for washing and hygiene is poor. Droughts affect food production. Its consequences are mostly indirect, leading to poor nutritional status, starvation, and undernourishment. There is an increased incidence of diarrhoeal diseases, micronutrient deficiencies, scabies, conjunctivitis, and trachoma. under nourishment, increased susceptibility to infection. Higher soil temperatures can promote fungal growth. Dry conditions are associated with wildfires and smoke. Rising sea levels inundate low-lying areas, leading to environmental exodus and salinate the land.

Ozone

There is an increase in ground-level ozone formed chemically from temperature-dependent precursor pollutants (nitrogen oxide, volatile organic compounds from power plant emission, and automobile exhaust, in the presence of light and higher temperatures. Ozone decreases lung function, irritates the conjunctiva and mucosa of the upper respiratory passages, and induces asthma and pulmonary oedema.⁸ A rise in local air pollution and warm weather together act as risk factors for the increased incidence of chronic obstructive pulmonary disease (COPD).

Experimental studies have shown that a higher concentration of carbon dioxide leads to an increase in the production of pollens and ragweed (Ambrosia artemisiifolia). Doubling the levels of CO₂ from 300 to 600 ppm is likely to cause a four-fold increase in the level of this highly allergenic pollen.₉ Global warming leads to an increase in the concentration of radon in the lower layers of the atmosphere.₁₀ Radon being a source of alpha radiation, this radioactive gas is likely to increase the occurrence of bronchogenic carcinoma.

Diseases

Global warming associated with rainfall, humidity, waterlogging, and active photosynthesis of vegetation is changing the ecology of many arthropod vectors that transmit diseases to humans. There is the emergence or resurgence of a variety of infectious diseases. Among them, diseases that are indirectly transmitted rank first. These diseases require either a vehicle for transfer from host to host (e.g., water- and food-borne diseases) or an intermediate host or vector as part of its life cycle. Most vector-borne diseases involve arthropod vectors (e.g. mosquitoes, flies, ticks, or fleas). Being cold blooded insects, any slight temperature change can have a potentially large biological effect on the transmission of diseases. Warmer temperatures increase mosquito, sandfly, and tick vector overproduction, biting, and transmission of diseases such as malaria, dengue, leishmaniasis, Rift Valley fever causing hemorrhagic fever syndrome, and tick-borne Lyme disease.¹¹ The hot summer months facilitate the spread of West Nile virus through bites of mosquitoes across the Western hemisphere. Unsafe domestic water storage practices in unusually warm and dry conditions facilitate viral development, such as chickungunya, in Aedes mosquitoes.

Since the anopheles mosquitoes have no control over their temperature regulation system, a rise in humidity or ambient temperature can have a sustained influence on their activity, dispersal, and spread. The tropical zones in which malaria has the potential to spread will grow through climate change. Malaria is a highly climate-sensitive tropical disease.  Dengue fever spread by the mosquito, Aedes aegypti has already widened its geographical boundaries in tropical regions. Aedes is strongly influenced by climate, including variables in temperature, moisture, and solar radiation. Any small increase in temperature that facilitates viral introduction into a susceptible human leads to an increased chance of an epidemic. The spread and activities of sandflies, vectors of leishmaniasis, are strongly influenced by ambient temperature. There is an explosion in the mouse population after heavy rainfall, and they may increase the chances of an outbreak of Hantavirus pulmonary syndrome. Extreme flooding with an increased population of rodents can lead to an outbreak of leptospirosis.

Successful stabilization of carbon dioxide emissions, vector control programme, relocation of the human population, and vaccination are to be undertaken to control such diseases.

Heavy rain can increase the risk of outbreaks of waterborne diseases. Fecal contamination of drinking water has led to epidemics of cholera. The discharge of excess wastewater directly into surface water bodies contaminates drinking water and leads to infections with Escherichia coli and Campylobacter jejuni.¹² The contamination of drinking water by a protozoan, Cryptosporidium parvum, can occur, which can lead to increased morbidity and mortality.¹³ This is especially noted in developed countries.  Warming of the Great African Lakes has been considered a possible cause of an increased risk of cholera outbreaks on the land in its vicinity.¹⁴ Neisseria meningitidis, the pathogen of meningococcal meningitis, is carried by dust particles and occurs during dry seasons. The El Nino effect that causes a prolongation of dry periods leads to a wider spread of pathogens in African countries, and its epidemics strike every 5 to 10 years.¹⁵ Due to the El Nino event, even the winter temperatures in Lima, Peru have increased by more than 5.0°C above normal and it has been observed that for every degree centigrade rise in air temperatures above normal, there is an increase in hospital admissions for childhood diarrhoea by 8%.¹⁶

Climate change in the coming years threatens the human population with health hazards by disrupting water and food supplies and increasing the spread of vector-borne diseases. It has called for the reduction of greenhouse gas emissions, by reducing fossil fuel combustion, the development of renewable energy technology, the establishment of stations equipped with remote sensing (RS) and geographic information systems (GIS) to monitor sea level rise and extreme weather conditions. Other actions include education programs in public healthcare and ongoing preventive measures and control measures for diseases that are spread by vectors or are caused by poor nutrition.⁵

Health risks form one of many sectors expected to be affected by climate and ecological changes. To optimize prevention capabilities, upstream environmental approaches must be part of any intervention, rather than assaults on individual agents of disease.¹⁷

The draft of the Kyoto Protocol in 1997 by the UN Framework Convention on Climate Change (UNFCCC) has called on industrialized nations to implement an effective strategy to reduce emissions and stabilize greenhouse gas concentrations in the atmosphere.¹⁸ It is the first step to stop the warming of the atmosphere of the Earth. The replacement of fossil fuels with renewable energy sources brings about stability in the greenhouse effect and indirectly alleviates its effects on public health. It needs a sincere global effort by all nations to prevent the disaster predicted 157 years ago. Otherwise, the statement of American author Charles Dudley Warner, ‘Everybody talks about the weather, but nobody does anything about it’ remains unchanged.

Through increased cooperation, the World will be better prepared to cope with climate-related health challenges. The actions include strengthening surveillance and control of infectious diseases, ensuring safe use of diminishing water supplies, and coordinating health actions in emergencies.

Conflict of Interest

None