Climate Hazards Have Made Half Of Known Infectious Diseases Worse

A new study has found that over half of the known infectious diseases to humans are being aggravated by climate change.

Of the 375 known human diseases that spread through pathogens, 218 are affected due to climate-related impacts, the study by a group of environment and health scientists that was published in Nature showed.

The team reviewed decades of scientific papers and traced evidence of the impacts of climate change on all pathogenic diseases.

"The numbers were jarring," the authors wrote in a post on Conversation explaining their study. "Flooding, for example, can spread hepatitis. Rising temperatures can expand the life of mosquitoes carrying malaria. Droughts can bring rodents infected with hantavirus into communities as they search for food."

The authors observed that there are 1,006 unique pathways in which climate hazards led to pathogenic diseases. And it is unlikely that the world will be able to adapt to this increased risk.

"The human pathogenic diseases and transmission pathways aggravated by climatic hazards are too numerous for comprehensive societal adaptations, highlighting the urgent need to work at the source of the problem: reducing greenhouse gas emissions," the study said.

The largest number of diseases aggravated by climate change were those that spread through a vector like mosquitoes, bats or rodents. Majority of them were associated with atmospheric warming, heavy rainfall, and flooding.

While in several cases climate hazards exclusively aggravated the disease risk, there were also instances were the impact of disease was also diminished. That said, such cases are a very small portion.

At its most basic level, infectious diseases spread when a pathogen—any disease carrying organism—comes in contact with a person. Climate events make that more likely, the authors explain.

For instance, warming weather at higher altitudes allows viruses to survive winters, in turn aggravating outbreaks such as Zika and dengue.

Habitat disruption from heatwaves, wildfires, storms and floods are associated with bringing pathogenic species closer to people. The authors cite spillovers from the Nipah and Ebola viruses to be associated with wildlife like bats and rodents moving to larger areas to forage for food.

There are also cases where climate events cause the pathogens to strengthen and become more severe. "Warming, for instance, had positive effects on mosquito population development, survival, biting rates and viral replication, increasing the transmission efficiency of West Nile virus."

Climate hazards also impair the human body's ability to fight off pathogens. Rapid and unpredictable weather changes, which are linked to higher greenhouse gas emissions, were linked to cases of reduced resistance to various diseases.

"For instance, failure of the human immune system to adjust to large changes in temperature was suggested as a likely mechanism to explain outbreaks of influenza," the study said.

The authors call for an urgent need to reduce emissions and improved understanding of the pathways in which climate impacts diseases.

"In our view, to dial back the risk, humanity will have to put the brakes on the human-caused greenhouse gas emissions fueling global warming."