Climate change is expected to weaken humans, supercharge pathogens, and push both to a closer level.
A new study shows that extreme weather conditions, ocean changes and soil upheavals have already contributed to the spread of more than 200 pathogens.
Three graphs show how extreme climate and environmental changes help spread the disease.
The first outbreak of the Nipah virus, a deadly disease spread by bats, may have started with a fire.
In 1997 and 1998, catastrophic wildfires erupted across Indonesia, punctuating a protracted drought and, many scientists suspect, pushing fruit bats from their forests to Malaysia. There, it is said, the increased bat population was attracted to fruit trees in pig farms.
Pig farmers soon began to develop fevers, headaches, sore throats, vomiting and swelling of the brain. People in Singapore who ate Malaysian pork also developed symptoms. Overall, more than 300 people fell ill and more than 100 died. To curb the disease, more than 1 million pigs have been culled and pig farming has been permanently banned in some regions.
Nipah virus is just one of 218 infectious diseases that have spread most widely among humans due to climatic extremes – floods, droughts, heat waves, hurricanes, ocean chemistry, sea level rise or other sensitive environmental conditions. to climate change – according to a study published in the journal Nature Climate Change on August 8.
“I can tell you that story with bats, I can tell you that story with birds, I can tell you that story with rats, mice, deer. And I can tell you about viruses and bacteria. And I can tell you through heat waves, floods, fires, even hurricanes, things that actually force those species to move, ”Camilo Mora, a data scientist at the University of Hawaii Manoa who led the study, told Insider.
By evaluating historical records of infectious diseases dating back to the Roman Empire, Mora’s team cataloged cases of climatic extremes that facilitated the spread of 58% of known human pathogens.
“I wasn’t expecting such a high number,” Mora said.
This is likely to be undercounted, he added, as it only includes instances documented in published articles. While not all of these cases can be attributed to current human-caused climate change, 80% of the articles are relatively recent, published in the past 20 years. They are based on a mountain of evidence that the extreme changes brought about by rising global temperatures help spread infectious diseases through three main pathways.
Route 1: Extreme weather conditions and land disintegration spread diseases by pushing animals and people closer
In Siberia in 2016, an anthrax outbreak was traced to a decades-old reindeer carcass unearthed by melting permafrost. It is an extreme case of climate change that creates new contacts between humans and infectious diseases, but the phenomenon is widespread.
Extreme weather events, which are becoming more frequent and severe with climate change, can displace animal and bird populations, bringing them closer to humans. The Nature study found that vector-borne diseases, those transmitted by animals and insects, were the most aggravated by climatic extremes.
Land use changes, such as deforestation, can bring animal populations to places where people live or bring humans to animal territory. In the eastern United States, studies suggest that dividing forest land for development has led to greater overlap between humans and ticks, facilitating the spread of Lyme disease.
Even extreme weather conditions can put humans in close contact with each other. Hurricanes and cyclones often lead to outbreaks of cholera, norovirus, and other deadly diseases. Such outbreaks were well documented in the aftermath of Hurricane Katrina. Floods can expose people to waterborne diseases such as vibriosis. A 1995 analysis even found that the spread of leprosy in Malawi was not associated with population density, but with rainfall.
Route 2: Extreme heat and rain can overload pathogens
Mosquitoes thrive in high temperatures and heavy rainfall, which create standing water where they can lay their eggs. Spreading diseases, such as malaria, West Nile virus, and chikungunya, thrive as climate change raises temperatures and heavy rainfall events in many parts of the globe.
The same pathogens can become stronger even in extreme conditions. Warming oceans are creating breeding waters that are fertile for vibro bacteria, which show signs of increased virulence with heat, allowing them to cause more serious disease.
Extreme heat waves, for example, can kill many infectious viruses, bacteria, fungi, and the creatures that spread them. Whatever survives, however, is adapted to extreme heat, including the fever our body produces to kill pathogens.
“Those that survive will survive 42 degrees Celsius, which means that when they come and infect us, one of the main mechanisms for us to fight these diseases and pathogens is not effective at all,” Mora said.
Route 3: Extreme weather weakens infrastructure and makes humans prone to disease
Humans and their infrastructures are more vulnerable to the devastating impacts of disease when they are compromised by extreme weather conditions. Smoke from fires, for example, can irritate the lining of the lungs, cause inflammation, inhibit the immune system, and make people more vulnerable to respiratory diseases such as COVID-19.
Extreme weather events such as heat waves can affect access to healthcare, making it difficult or dangerous for people to leave their homes or destroying necessary infrastructure. Just this summer, the heat melted airport roads and asphalts, warped railways and caused power outages.
People affected by rapid weather variability or extreme events such as hurricanes or fires could be stressed, leading to elevated cortisol levels that weaken their immune systems. Malnutrition, which is expected to become more prevalent as climate change hits bread baskets around the world, has a serious negative impact on the immune system.
Adapting infrastructure, contingency planning and healthcare to these new extremes can reduce the spread of disease. But the Nature study concludes that pathogens driven by climate threats “are too numerous for global social adaptations.” Instead, the authors write, their findings highlight “the urgency to work at the source of the problem: reduction [greenhouse gas] emissions “.
“Keep in mind that this isn’t some strange alien causing climate change,” Mora said, adding, “It’s the contribution of the little things you and I do, multiplied by nearly 8 billion people.”
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