Across the planet, animals — and the diseases they carry — are shifting to accommodate a globe on the fritz. And they’re not alone: Ticks, mosquitos, bacteria, algae, even fungi are on the move, shifting or expanding their historical ranges to adapt to climatic conditions that are changing at an extraordinary pace.

These changes are not happening in a vacuum. Deforestation, mining, agriculture, and urban sprawl are taking bites out of the globe’s remaining wild areas, contributing to biodiversity loss that’s occurring at a rate unprecedented in human history. Populations of species that humans rely on for sustenance are dwindling and getting pushed into ever-smaller slices of habitat, creating new hotspots for diseases to jump from animals to humans.

Meanwhile, the number of people experiencing extreme repercussions of a warming planet continues to grow. Climate change displaces some 20 million every year — people who need housing, medical care, food, and other essentials that put strain on already fragile systems that are growing ever more stressed.

All of these factors create conditions ripe for human illness. Diseases old and new are becoming more prevalent, and even cropping up in places they’ve never been found before. Researchers have begun piecing together a patchwork of evidence that illuminates the formidable threat climate-driven diseases currently pose to human health — and the scope of the dangers to come.

Read more in Daily Maverick: Urgent course correction needed on climate change, economic policy and NHI

Rising temperatures

“This is not just something off in the future,” Neil Vora, a physician with the nonprofit Conservation International, said. “Climate change is here. People are suffering and dying right now.”

Research shows that climate change influences the spread of disease in a few major ways.

To escape rising temperatures in their native ranges, animals are beginning to move to higher, cooler elevations, bringing diseases with them. That poses a threat to people living in those areas, and it also leads to dangerous intermingling between animal newcomers and existing species.

Animal migration

Bird flu, for example, has been spreading with greater ease among wild animals as rising seas and other factors push nesting bird species inland, where they’re more likely to run into other species. Diseases that jump between species tend to have an easier time eventually making the leap to humans.

Warmer winters and milder autumns and springs allow carriers of pathogens — ticks, mosquitos, and fleas, for example — to remain active for longer swaths of the year. Expanded active periods mean busier mating seasons and fewer casualties over the cold winter months. The Northeastern United States has seen a massive proliferation of Lyme disease-carrying black-legged ticks over the past decade, with warmer winters playing a decisive role in that trend.

Extreme weather

Erratic weather patterns, such as periods of extreme drought and flooding, create conditions for diseases to spread. Cases of cholera, a water-borne bacterial disease, skyrocket during the monsoon season in South Asian countries when flooding contaminates drinking water, especially in places that lack quality sanitation infrastructure. Valley fever, a fungal-borne infection caused by spores that grow in the soil in the Western US, proliferates during periods of rain. The severe drought that tends to follow rain in that part of the world shrivels the fungal spores, which allow them to more easily disperse into the air at the slightest disturbance — a hiker’s boot, say, or a garden rake — and find their way into the human respiratory system. DM

To read all about Daily Maverick’s recent The Gathering: Earth Edition, click here.