We are witnessing impacts of climate changes in a variety of ways. Almost every day, in one or other part of the globe, more frequent and intensifying weather and climate events are observed, including storms, extreme heat, floods, droughts and wildfires. This year, as summer continues in the Northern Hemisphere, we are facing the relentless and devastating power of extreme heat waves. Our country is literally burning. Delhi touched a record temperature of close to 500 C. There were reports of forest fires, of buildings going up in flames, of electrical equipment burning.

Surprisingly, even leaves are being burnt to a crisp. In fact, the heat wave is a national emergency. Above all, it remains a fact that the extraordinary Indian summer could be a warning message to the world. In Saudi Arabia, the extreme heat wave turned the sacred Haj pilgrimage into a perilous journey. In the US over 80 million people are under heat alert. The Balkans and the Mediterranean regions are also reeling under blistering effects of heat waves. What is a matter of serious concern is that the World Meteorological Organisation has predicted that future years will likely surpass current temperature records. The world is on the boil and all this will only get worse, not just in India but across the world. Global warming has put humans in a situation which could metaphorically be compared with the boiling frog syndrome.

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A frog is put in a vessel of water and the vessel is slowly heated. As the temperature of the water rises, the frog is able to adjust its body temperature accordingly. Thus, the frog keeps on adjusting with increase in temperature. But just when the water is about to reach boiling point, the frog is not able to adjust anymore. At that point, the frog tries to jump out of the vessel, but in vain because the frog has lost all its strength in adjusting with the rising water temperature. Eventually, the frog is boiled alive. The tale is often told as a metaphor for the inability or unwillingness of people to react or to be aware of the sinister threats that arise gradually rather than suddenly. Global temperature has not increased suddenly. It has changed gradually.

Our situation is a bit like the proverbial frog. The syndrome teaches us that unlike the frog, had we taken appropriate decisions vis-à-vis timely actions we could have escaped the fate faced by the frog. We are quite aware of the fact of gradual rises in global temperature, dire consequences of global warming and have also heard prophecies of experts. But we have ignored these, as Cassandra’s prophecies were ignored that led to the fall of Troy. In his address at the UN Climate Change Conference UK 2021, then British Prime Minister Boris Johnson aptly said: “Humanity was caught napping by coronavirus. But for climate change, nobody can say we have not been warned.

And nobody can say we are not now capable of making the preparations.” Notwithstanding our awareness, global warming continues relentlessly. We have to accept that heat is here to stay and will only get worse. Hence we need to understand how much heat humans can tolerate. Scientists believe that this range is 400 C to 500 C. But it depends on how temperature ~ acclimatized our bodies are; on whether the heat is dry or wet ~ accompanied by high levels of moisture (H2O vapour) in the air, which makes it more unbearable, and, of course, on the condition we live in. Weather and climate hazards affect our health both directly and indirectly, increasing the risk of death, non-communicable diseases, the emergence and spread of infectious diseases, and health emergencies. Since the 19th century, human activities have increased greenhouse gases ~ predominantly carbon dioxide, methane, and nitrous oxide ~ in the Earth’s atmosphere and have resulted in global warming (greenhouse effects).

Fundamentally, climate shocks and growing stresses such as changing temperature and precipitation patterns, droughts, floods, and rising sea levels degrade the environmental and social determinants of physical and mental health. All aspects of health are effected by climate change, from clean air, water and soil to food systems and livelihood. WHO data shows around 2 billion people lack safe drinking water and 600 million suffer from food-borne illness annually. Climate stressors heighten water and food-borne disease risks. In 2020, around 700 million faced hunger, predominantly in Africa and Asia. Floods not only have direct effects but also increase the risk of microbiological water pollution. Global warming affects water heating and transmission of water-borne pathogens. The high sea surface temperature and sea level rising may cause waterborne infections and toxin-related illness such as cholera and shellfish poisoning.

Higher temperature may also facilitate the introduction of new pathogens, vectors, or hosts (food chain). Without preventive measures, deaths from vector-borne diseases, currently over 7 lakh annually, may rise. The transmission of infectious diseases through vectors is very complex, particularly when humans or livestock are not the only reservoir. But it is abundantly clear that the key elements in the epidemiology of vectorborne diseases include the ecology and the behaviour of the host, the ecology and behaviour of the carrier, and the level of immunity of the population. Pathogens transmitted by vectors are particularly sensitive to climate change because they spend a good part of their life cycle in a cold blooded host invertebrate whose temperature is similar to the environment.

So, a warmer climate facilitates favourable conditions for the survival and completion of the life cycle of the vector, going as far as to speed it up as in the case of mosquitoes. It has been observed that in warmer areas the percentage of maturation of insects from larval form to adult form increases and the time required for maturation also decreases. Mosquitoes are now found worldwide, except in regions permanently covered by ice. There are about 3,500 species of mosquitoes, almost three quarters of which are present in tropical and sub-tropical wetlands. Mosquitoes typical of temperate regions have had to develop strategies to survive the winter, as well as pathogens that can be transmitted.

In tropical regions, similarly, adaptation was needed to survive at the time of prolonged drought. However, in both cases, these adaptive mechanisms have also affected the reasonability of transmission. Globally, in 2022, there were an estimated 249 million malaria cases and 608,000 deaths in 85 countries. The African Region carries a disproportionately high share of the global malaria burden. Zika virus is primarily transmitted by the bite of an infected mosquito from the Aedes genus, mainly Ades aegypti, in tropical and subtropical regions. Recently, this virus has emerged as a ‘public health emergency of international concern’, according to WHO. Ticks are responsible for the transmission of both viruses and bacteria.

Rising temperature accelerates the cycle and of the development, production of eggs, and the density and distribution of their population. It has already been established that rise in temperature could lead to change in the population of Ixodes ricinus, a vector of viral infections such as ticks–borne encephalitis and Lyme disease in Europe. A mysterious chronic kidney disease ~ CKDu ~ which is characterised by progressive loss of kidney function is usually reported among those suffering from diabetes, hypertension and kidney inflammation. But scientists have so far not been able to pinpoint what causes CKDu. Now researchers have established that heat stress and dehydration are the major driving forces of this mysterious chronic kidney disease.

Some people are more vulnerable than others to the effects of climate change on health. In fact, climate-sensitive health risks are disproportionately felt by the most vulnerable and disadvantaged, including women, unborn babies, children, ethnic minorities, poor communities, migrants or displaced persons, older populations, and those with pre-existing medical conditions. Climate change has been described by the WHO as the biggest threat to health in the 21st century ~ it affects our health and wellbeing in many ways. It makes many existing diseases and conditions worse.

The Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) concluded that climate risks are appearing faster and will become more severe sooner than previously expected, and it will be harder to adapt with increased global heating. Research shows that around 3.6 billion people already live in areas highly susceptible to climate change. Between 2030 and 2050, climate change is expected to cause approximately 2.5 lakh additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress alone.

We should remember some hard facts: no one is safe from climate change risks, global heating of even 1.50 C is not considered safe, and every additional tenth of a degree of warming will take a serious toll on people’s lives and health. To make the planet liveable, it is also imperative that every individual contributes to safeguarding the present as well as the generations to come from the perils of climate change. As Al Gore, the Nobel Peace Laureate, said: “I cannot stand the thought of leaving my children with a degraded earth and a diminished future.”

(The writer is a retired IAS officer)