At the time of this writing, the number of people infected with COVID-19 worldwide has passed one and a half million. The number of dead is nearing 100,000, and both of these numbers are increasing daily. The global economy has essentially gone into hibernation as countries lock down their populations in an attempt to slow the spread, and currently there is no end in sight for the global crisis.

COVID-19 was transmitted from animals to humans (most likely by way of bats) in Wuhan, China, according to a Scripps Research Institute study titled “COVID-19 coronavirus epidemic has a natural origin” and published March 17. But, the circumstances that enabled the global spread of the virus can be broken down into natural and distinctly unnatural components: a worsening climate crisis and human encroachment on the wilds, both of which bring humanity into contact with viral pathogens that is too close for comfort.

Calling the COVID-19 outbreak a once-in-a-lifetime event would be an understatement. Occurring 102 years after the Spanish Flu wreaked havoc across the globe, it is once-in-a-century.

But, can we expect global pandemics to remain at that frequency of occurrence?

Human Behavior as a Vector

Epidemiologists refer to agents that carry and transmit infectious pathogens to other living organisms as “vectors”. In the case of COVID-19, humans are vectors that, thanks to international air travel, the global economy, and the largely inadequate (though greatly varied) responses of governments, have transmitted the disease through movement.

“Never before have so many opportunities existed for pathogens to pass from wild and domestic animals to people,” United Nations (UN) Environmental Programme director Inger Andersen told The Guardian recently—not only by way of humanity’s insatiable appetite for travel, but via habitat loss and human encroachment.. In fact, the 2001 study “Risk factors for human disease emergence” showed that 75 percent of all emerging infectious diseases come from wildlife. Anderson agrees, noting that “Our continued erosion of wild spaces has brought us uncomfortably close to animals and plants that harbor diseases that can jump to humans.”

In this context, Professor Andrew Cunningham of the Zoological Society of London reflected, in the same article, that, “The emergence and spread of COVID-19 was not only predictable, it was predicted [in the sense that] there would be another viral emergence from wildlife that would be a public health threat.”

Indeed, certain red flags have warned us of an impending crisis like COVID-19 for years. The outbreaks of Severe Acute Respiratory Syndrome (SARS) in 2002-2003, Middle East Respiratory Syndrome (MERS) in 2012, and Ebola in 2014 each provided warnings to global governments that went unheeded in the years preceding COVID-19. The warning was this: worsening habitat destruction from development, deforestation, the climate crisis, and for-profit animal exploitation inevitably lead to humans becoming infected with “zoonoses”, or diseases transmitted from animals they would have otherwise never come into contact with.

COVID-19 is simply the next round of disease driven by deleterious human actions against the Earth.  Cunningham went so far as to say we “probably got a bit lucky” with COVID-19, given that the fatality rate for Ebola was 50 percent and the Nipah virus had a fatality rate between 60 and 75 percent. He, like many scientists, believes that there will be more pandemics in the future unless we change our behavior, including our bringing of vast numbers of wild animals into markets where they have direct contact with one another and with humans.

“With people in large numbers in the market and in intimate contact with the body fluids of these animals, you have an ideal mixing bowl for [disease] emergence,” Cunningham said. “If you wanted a scenario to maximise the chances of [transmission], I couldn’t think of a much better way of doing it.”

Science writer David Quammen sounded the alarm in his 2012 book Spillover: Animal Infections and the Next Human Pandemic, in which he called for governments and health sectors to prepare for incoming pandemics. “Beware of a new virus, maybe a coronavirus, emerging from a wild animal, maybe a bat. Those were the warnings I put into Spillover,” Quammen told Orion Magazine. His concise tips on what to expect and what needs to be done are worth repeating:

This is why Andersen said that the proper thing to do now must be to stop the loss of habitat and biodiversity loss from the ongoing expansion of human population and the economy.

She cited the wildfires that ravaged Brazil and Australia during the last year as examples of human action setting the stage for pandemics, linking the fires in the Amazon directly to Brazilian President Jair Bolsonaro’s tactics of working in the interests of the ranching and agribusiness sectors— made necessary, of course, by increasing global temperatures from the climate crisis that are factoring in to the loss of habitat.

Just as Quammen warned, Andersen says that it is precisely this continued erosion of space for wildlife that has brought us too close to the animals and plants that harbor deadly diseases that can make the jump to humans, as happened with COVID-19.

Even the World Bank has echoed these sentiments. “The origin and pathway of the coronavirus pandemic shouldn’t surprise us,” environmental specialist Daniel Mira-Salama wrote in a World Bank blog recently. “The SARS epidemic in 2003 jumped to humans from civet cats, sold in markets as pets and as a delicacy. MERS was transmitted to humans from camels in 2012. Avian influenza, Nipah virus, Ebola, HIV… all of these and many other Emerging Infectious Diseases (EIDs) originated in animals and were transmitted to humans.”

Cunningham described the current global pandemic as “a clear warning shot”, and added, “It’s almost always a human behavior that causes [pandemics] and there will be more in the future unless we change.”

But even now, many countries are continuing to weigh protecting their economies against the full-scale measures that need to be taken to actually contain the spread of the coronavirus.

By way of example, the United States has set itself up to become the basket-case of the COVID-19; even White House models show that 2.2 million Americans could have died if nothing were done, and up to 240,000 even despite the measures that have been put in place..

While the United States is taking measures to contain the virus now, it was only after months of ignoring the true scope of the threat, giving the virus time to deeply infiltrate communities across the country. Wide-scale testing still lags, and while states like Washington State have implemented lockdowns and are seeing some success in slowing the spread, states like Florida have reacted softly by comparison.

Hence, without uniformly serious response nationally, it appears inevitable that the virus will continue to spread rapidly, just as we saw in Europe early on.

Climate as a Vector

Alongside human encroachment of wildlife habitat, the other most important factor at play in how we have set ourselves up for the inevitability of pandemics is the accelerating climate crisis.

The climate crisis presents a two-pronged threat of future pandemics: by way of shifting temperatures and rainfall patterns that allow diseases and their vectors to move into regions that previously did not support their existence, and by accelerated rates of thawing that release already-incubated diseases from frozen material.

Diseases and pathogens frozen deep within Arctic permafrost are already being released as global warming forces permafrost to thaw. In August 2016, a young boy died and 20 others were hospitalized in Siberia after being exposed to anthrax released from thawing permafrost. The source was an infected reindeer carcass that had been frozen 75 years earlier, which thawed during the summer heat wave of 2016. The anthrax was released into the water and soil where other reindeer—part of the Siberian diet—grazed, thereby exposing the human population.

Scientists fear that thawing permafrost is like opening a Pandora’s Box of diseases. “Permafrost is a very good preserver of microbes and viruses, because it is cold, there is no oxygen, and it is dark,” evolutionary biologist Jean-Michel Claverie with Aix-Marseille University in France told the BBC in May 2017. “Pathogenic viruses that can infect humans or animals might be preserved in old permafrost layers, including some that have caused global epidemics in the past.”

Thawing permafrost, shifting temperature and rainfall patterns, and human encroachment on wildlife habitats have coalesced not only to create prime conditions for COVID-19, but have virtually guaranteed greater frequency and increased lethality of future global pandemics if radical changes are not made in humans’ current relationship to the planet.

A 2011 study published in the journal Global Health Action warned, “As a consequence of permafrost melting, the vectors of deadly infections of the 18th and 19th centuries may come back, especially near the cemeteries where the victims of these infections were buried.”

A NASA study from 2005 proved it was possible to revive bacteria that had been frozen for 32,000 years, and in 2007 scientists revived bacteria from Antarctica that had been frozen for eight million years.

While not all bacteria can survive a lengthy deep-freeze, many can, and those we know of bring cause for alarm, not even speaking of those we have yet to learn about.

Another endeavor, this one from 2014, managed to revive two viruses that had been in the deep freeze of permafrost in Siberia for 30,000 years. They became infectious shortly thereafter.

Claverie stated that there is a distinct probability that microbes carrying pathogens could be revived, as studies have shown, and told the BBC, “It could be bacteria that are curable with antibiotics, or resistant bacteria, or a virus. If the pathogen hasn’t been in contact with humans for a long time, then our immune system would not be prepared. So yes, that could be dangerous.”

According to the World Health Organization (WHO), there are three main ways of looking at links between infectious diseases and the climate crisis.

First, we can examine past associations between climate variability and the occurrence of infectious disease, such as dramatic increases of malaria alongside extreme weather events; for example, climate-intensified monsoons in India have brought higher rainfall and humidity, sparking dramatic malaria outbreaks.

Similarly, we can examine these early indicators of increased disease vulnerability—including temperature extremes and extreme weather events—in isolation as they continue to emerge.

By using evidence from these two studies, it is possible to create a predictive model that estimates the burden of future infectious diseases alongside projected climate scenarios. Some models show an (obviously expected) increase of malaria globally as overall temperatures continue to warm and humidity and extreme rainfall events increase.

“The malaria modeling shows that small temperature increases can greatly affect transmission potential,” the WHO stated. “Globally, temperature increases of 2-3 degrees Celcius would increase the number of people who, in climatic terms, are at risk of malaria by around 3-5 percent, i.e. several hundred million. Further, the seasonal duration of malaria would increase in many currently endemic areas.”

Other examples abound. In 2012, the United States saw the worst outbreak of the West Nile virus in the country’s history, in which 19 people in the greater Dallas, Texas, area died due to the multiplication of infected insects in warmer-than-average summer temperatures.

The danger of warming lies in its ability to amplify both infectivity and replication of viruses, researchers have found. Robert Haley, director of epidemiology at the University of Texas Southwestern Medical Center and co-author of a major study on the 2012 West Nile virus outbreak, told the media, “If everything else stays the same, you could predict that a warmer climate makes things worse.”

“The warmer the planet gets, the more pathogens and vectors from the tropics and subtropics are going to move into the temperate zones,” Daniel Brooks, an evolutionary biologist with the University of Nebraska, told The Washington Post in November of 2015. “Countries such as the United States tend to have a false sense of security, but vectors and pathogens don’t understand international boundaries. You can’t just put up a fence to keep them out.”

In short, diseases that used to be largely confined to the equatorial region are spreading northwards and southwards into regions previously uninhabitable to them—and the populations of hundreds of millions, if not billions, of humans are waiting as prime hosts.

In another example, a 2013 study showed clearly that unusually warm winters consistently tend to be followed by earlier and more intense flu seasons the following year; yet another study from this year warned that dramatic and rapid swings in weather patterns are also a contributor towards worsening flu epidemics. This should give us great pause, given that 19 of the 20 hottest years ever recorded have occurred since the year 2000, and the last six years have been the six warmest ever recorded.

Meanwhile, ocean temperatures are also increasing at unprecedented rates, wildfires and droughts of increasing severity and frequency are erasing forests around the globe, and the frozen areas of Earth are thawing and melting at ever-accelerating rates. Extreme weather events are occurring more frequently; Hurricane Harvey struck Houston, Texas in 2017, and dumped so much rain that the water actually depressed the Earth’s crust by two centimeters in that region.

Discussing these phenomena in the context of the West Nile virus, Brooks said that “biology is notoriously nonlinear and full of thresholds beyond which all hell breaks loose, at least for a while”—what now feels like a prophetic warning about COVID-19. “Think of a heart attack as an analogy. You can feel pretty good right up the point that you die.”

Even without pathogens, life on a climate-disrupted planet is going to be increasingly challenging, as food and water shortages, increasing military conflicts, and massive displacements of humanity driven by rising sea levels, droughts, and extreme weather events continue to pick up pace.

Moreover, the economic machinery of the planet continues to deforest, mine, burn, and encroach upon habitats that are carrying pathogens which, though unknown, could even be even more disastrous than COVID-19.

“I think we can say that things are going to change, and that we expect the risk to increase,” Christine Johnson, director of the EpiCenter for Disease Dynamics at the University of California, Davis’ School of Veterinary Medicine was quoted in an E&E News article this March. “But we can’t say with any certainty which diseases, in which locations and at which time.”

From this ongoing, unchecked process of climate change, the stage was set for COVID-19—and it remains set for more, and likely far worse, pandemics in the future.