Four ways climate change affects over 200 diseases

That climate change is increasingly affecting our lives is quite evident.

But now, a team from the University of Hawaii, in the United States, has released a study that shows how they impact more than 200 existing diseases.

The study, published in August this year in the scientific journal Nature, began with the aim of finding out whether climate change could have influenced the emergence and spread of Covid-19.

But it ended up being expanded during the process, and the scientists cross-referenced data with more than 70,000 scientific articles and the incidence of climate change on diseases.

Colombian Camilo Mora, professor in the Department of Geography and Environment at the University of Hawaii, led this study.

“Climate change has complicated 58% of all the diseases that exist in humanity”, says Mora. “Many diseases that already exist, but that may have been made worse.”

The scientist uses a hypothetical scenario to help explain the relationship: “I may feel strong, but suddenly the [lutador americano] Mike Tyson. I can even put up with him, but he’s going to beat me up. But if there are three more like him in this same scenario, I won’t survive.”

“Our vulnerability in this regard is great,” he adds.

During the study, the authors claim to have found 3,213 empirical examples where climate change has affected pathogenic diseases.

Among the main phenomena caused by climate change, they listed four that most influence diseases: global warming (which affects 160 diseases), increased rainfall (122), floods (121) and drought (81).

Scientists have also found more than a thousand ways in which “climate threats, through different types of transmission, have resulted in cases of pathogenic diseases.”

They grouped them into four general processes, which relate to how the pathogen (the disease-causing agent) behaves and who is infected.

Approaching pathogens with humans

This process is related to the geographic migration of species due to climate change.

Due to rains, droughts, melting glaciers and other weather events, animals and all the pathogens they carry are forced to move.

According to Mora, this is what happens to bats that live in the jungle. “Due to a fire, for example, the bat can be forced to move and approach us – and, with it, all its pathogens”.

“Their habitat is being affected, it’s like we’re expelling the animals,” he says.

This movement increases the likelihood of contact between animals and humans and, therefore, the spread of disease.

Movement of humans closer to pathogens

Climate change has also led to the displacement of human beings, both temporarily and permanently, to places where the pathogenic agents that cause us various diseases are concentrated.

The increase in hurricanes or floods, for example, produce this phenomenon. “People are forced to walk in water or in the middle of a flood, which is full of bacteria and viruses. They basically go to meet the pathogen”, says Mora.

Thus, the contact between humans and pathogens increases and, therefore, the probability of having diseases associated with them.

Drought is another phenomenon that forces people to move.

“For example, in Africa, people must migrate to where there is water. In this movement, they transport animals and their pathogens — they all gather in the same place where the water is.”

And, once again, the likelihood of infections grows due to increased contact with pathogens.

Climate change is making some diseases worse

Changing climatic conditions in some places cause organisms and pathogens to die or adapt. By natural selection, only the strongest survive. And that directly impacts diseases.

For example, explains Mora, fever is a mechanism for fighting some diseases and “generates conditions that pathogens do not like.”

But as a result of increasingly frequent heat waves, pathogens are adapting to higher temperatures.

“A heat wave of 40ºC or 42ºC kills certain pathogens, but those that survive have the ability to withstand a higher temperature than normal human fever. In this way, the pathogen is already able to oppose a person’s natural defenses”, he explains. .

This same increase in temperature accelerates the reproductive cycle of some species.

The extension of the rainy season in some areas also facilitates the reproduction of mosquitoes, which are important vectors of diseases such as chikungunya, yellow fever or dengue.

“If the ideal conditions for mosquito reproduction are extended, for example, for two months, there are more opportunities for them to reproduce”, he says.

Climate change is weakening us and weakening our defenses

This phenomenon occurs through several mechanisms.

The first one relates to infrastructure and access to it. For example, “in the event of a hurricane or flood, the collapse of infrastructure means that we don’t have access to healthcare.”

But we are also affected on a bodily level.

To cite just one of the possible effects, climate change can generate an alteration in cortisol, the hormone that is activated in the face of danger to, in turn, awaken the “defense” or “escape” mechanism.

“Our immune system is affected and if we are infected, we will be less able to fight,” says Mora.

The most ‘benefited’

The diseases, which range from diarrhea to cardiovascular diseases, encephalitis or dermatitis, have some main causes: viruses and bacteria, “those that survive the longest”, explains Mora.

Transmission occurs mainly through water, air, direct contact or consumption of food.

“We analyzed the effect of climate change on each disease, but not the magnitude, how it spreads. Because this already depends on many conditions, such as the country’s culture, socioeconomic conditions or laws and their valuation, which is difficult to calculate”, says Mora.

But he points out that quantifying these factors “removes responsibility from the real culprit”: climate change.

Regarding the diseases contained in the study, he says that he usually keeps an eye out for those that are infectious, but there are others such as allergies — one of the most common is pollen allergy —, respiratory diseases or conjunctivitis that are aggravated by climate change, and we should be attentive to them.

Although the study indicates that there are some diseases (just over 60) that in some cases have improved with the effect of climate change, “it is difficult to look for hope”.

“The amount of suffering that we see in our article is very frightening,” says Mora.

He points out that the cases studied by his team already existed, but it remains to be seen “what will happen to us” if we don’t act and politicians don’t “stop thinking only with our brains and start putting a little heart into it”.