Hundreds of known infectious diseases are now worse than ever due to the climate crisis. Hazards such as flooding, heatwaves and drought have had a worsening impact on more than half of the hundreds of known infectious diseases in humans.
According to researchers, this applies to diseases including malaria, hantavirus, cholera and even anthrax. Researchers looked through the medical literature of established cases of illnesses and found 218 out of the 375 known human infectious diseases - 58% - seemed to be made worse by one of 10 types of extreme weather connected to climate change, according to a study in the Nature Climate Change journal.
Doctors dating back to Hippocrates have long connected disease to weather. Now this new study shows how widespread the influence of climate is on human health.
Researchers expanded their search to include infectious diseases and all types of human illnesses, including non-infectious sicknesses such as asthma, allergies and even animal bites. They found a total of 286 unique sicknesses of which 223 seemed to be worsened by climate hazards, nine were diminished by climate hazards and 54 had both aggravated and minimised cases, the study found.
The new study does not do the calculations to attribute specific disease changes, odds or magnitude to climate change, but finds cases where extreme weather was a likely factor among many. The study did map out the 1,006 connections from climate hazard to illness.
"If climate is changing, the risk of these diseases are changing," said study co-author Dr Jonathan Patz, director of the Global Health Institute at the University of Wisconsin-Madison. Doctors said they need to think of the diseases as symptoms of a sick Earth.
"The findings of this study are terrifying and illustrate well the enormous consequences of climate change on human pathogens," said Dr Carlos del Rio, an Emory University infectious disease specialist, who was not part of the study.
"Those of us in infectious diseases and microbiology need to make climate change one of our priorities and we need to all work together to prevent what will be without doubt a catastrophe as a result of climate change."
Study lead author Camilo Mora, a climate data analyst at the University of Hawaii, said the study is not about predicting future cases.
"There is no speculation here whatsoever," he said. "These are things that have already happened."
One example he knows first-hand. About five years ago, his home in rural Colombia was flooded - for the first time in his memory water was in his living room - and Mr Mora contracted chikungunya, a nasty virus spread by mosquito bites.
Even though he survived, he still feels joint pain years later. Sometimes climate change acts in odd ways.
Mr Mora includes the 2016 case in Siberia when a decades-old reindeer carcass, dead from anthrax, was unearthed when the permafrost thawed from warming. A child touched it, got anthrax and started an outbreak.
Mr Mora originally wanted to search medical cases to see how Covid-19 intersected with climate hazards, if at all. He found cases where extreme weather both exacerbated and diminished chances of Covid.
In some cases, extreme heat in poor areas resulted in people congregating together to cool off and be exposed to the disease, but in other situations, heavy downpours reduced Covid spread because people stayed home and indoors, away from others. Long-time climate and public health expert Kristie Ebi, at the University of Washington, said she had concerns about how the conclusions were drawn and some of the methods in the study.
It is an established fact that the burning of coal, oil and natural gas led to more frequent and intense extreme weather and research has shown that weather patterns are associated with many health issues, she said.
"However, correlation is not causation," she added. "The authors did not discuss the extent to which the climate hazards reviewed changed over the time period of the study and the extent to which any changes have been attributed to climate change."
But Dr Aaron Bernstein, interim director of the Centre for Climate, Health, and the Global Environment at Harvard School of Public Health, Dr del Rio and three other outside experts said the study is a good warning about climate and health for now and the future, especially as global warming and habitat loss push animals and their diseases closer to humans.
"This study underscores how climate change may load the dice to favour unwelcome infectious surprises," Dr Bernstein said. "But of course it only reports on what we already know and what's yet unknown about pathogens may be yet more compelling about how preventing further climate change may prevent future disasters like Covid-19."
