This is the opening scene—ground zero—in the 1995 film Outbreak, in which an Ebola-like virus ultimately lands on U.S. soil and becomes an unstoppable killer. In the film, the virus is connected directly to the deforestation of the land enacted by western military: a local health care worker tells a U.S. army virologist, played by Dustin Hoffman, that the local “juju man” believes “the gods were awoken by their sleep by the man cutting down the trees where no man should be, and the gods got angry; this is their punishment.”
In 2011, Steven Soderbergh’s Contagion looked anew at the same issues of global infection, and here too, the filmmakers came to the same conclusion: the source of the killer virus is (spoiler alert) also industrial deforestation. In the 21st century edition, a multinational bulldozes a grove of palm trees in China for some unnamed purpose, destroying the nest of some local bats. Those bats end up flying over a pig farm, dropping a piece of infected fruit into the pen. The pig eats the fruit, the humans eat the pig, and the next thing you know, the contagion is spreading.
These, and other, pop culture characterization of Ebola-like viruses place the blame for the spread of the disease squarely on the shoulders of globalization and man’s careless despoiling of the environment. It’s not just Hollywood that believe that we are the cause of our own potential demise.
“Humans are the major driver of emerging diseases,” says Jonathan Epstein, an epidemiologist at the non-profit EcoHealth Alliance who studies Ebola and other infectious disease. “Things like agricultural expansion and deforestation…and certainly travel and trade — these are things that manipulate our environment and allow pathogens to get from animal hosts to people and then travel around the world.”
In a study published in 2012, researchers asked national infectious disease experts in 30 different countries whether or not they thought climate change would affect infectious disease patterns in their countries. The majority agreed.
Nevertheless, it’s unclear whether these beliefs are driven by good science, or, as Malcolm Gladwell argued way back in 1995, a guilt-driven “idea of disease as a punishment for wickedness.”
It’s true that West Africa, where the latest and most catastrophic Ebola outbreak is currently raging, has faced unequivocal environmental changes in recent years. The International Food Policy Research Institute published a report in 2013, finding that in Sierra Leone (the epicenter of the outbreak), climate change has resulted in “seasonal droughts, strong winds, thunderstorms, landslides, heat waves, floods, and changed rainfall patterns.”
And there is, according to the World Health Organization, a recent global increase in infectious diseases that seems to correspond with rising global temperatures. But determining whether there is a direct causative relation between the two is a hazy business.
One issue at play is food scarcity. The Ebola virus is known to spread into human populations through contact with an infected animal. The virus can live for years in animal populations (such as bats and monkeys) without harming the animals, becoming dangerous to humans only when humans prepare and eat infected bush meat. Poorer populations, living in resource-strapped areas, are the most likely to become stricken with the virus—because they’re the ones most likely to rely on bush meat to feed their families. And according to the 2013 IFPRI report, “poor communities suffer the most from climate change impacts.” It’s not hard to extrapolate from there and estimate that as these communities become more and more needy, they will encroach further into the wild in search of food. These changes in human behavior will likely impact the natural environment.
“We we see more incursion into the forest, we might see more exposure to Ebola,” says Stephen Morse, an infectious disease and epidemiology expert at Columbia University. “But it’s unclear whether there would be a net positive or net negative.”
Morse believes that the only way to make an educated guess at how climate change will impact future Ebola outbreaks is to undertake nuanced microclimate analyses of the specific African regions that have been affected in the past. And even that might not say all that much, given that Ebola and other emerging diseases seem to pop up in new parts of the continent every few years.
On the other hand, research does suggest strongly that warming global temperatures will make vector-borne diseases like malaria more common, mostly because the vectors that carry those diseases — like mosquitoes — thrive in warmer climates.
In the past few century, the temperatures of the oceans have risen significantly, at an average of 0.13 degrees Fahrenheit per decade. And it turns out cholera thrives in warm water; research has shown that rising sea temperature seem to be connected to rising incidences of cholera. Further, as temperatures rise, the polar ice caps will continue to melt, leading to rising sea levels. The most dire prognosticators warn that low-elevation coastal zones
This is particularly problematic in developing countries. Globalization has led to significant change in the demographics in these parts of the world; in Africa, more and more people are moving out of the rural areas and into the growing cities. That, in turn, has had some serious public health consequences that look to worsen in coming years.
“As you move towards these megacities and mega populations on coastal areas, you wind up with huge vulnerability to infectious outbreaks because of inadequate sanitation and water,” says Stephen Morrison, the director of the Center for Strategic & International Studies’ Global Health Policy Center. “And then if you have flooding, those coastal environments will be more at risk because of climate change. You’ll be at a higher risk of the kind of infectious outbreaks like cholera.”
And the reality is that both malaria and cholera have had — and are expected to continue to have — a much bigger impact on public health than Ebola (unless the current outbreak becomes a truly once-in-a-lifetime, Hollywood-style pandemic). The WHO estimates about 110,000 deaths due to cholera every year; malaria killed an estimated 627,000 in 2012 alone. Meanwhile, since the first Ebola case was identified in 1976 there have been only 1,600 Ebola-related deaths.
That, though, is not exactly good news for human populations. Because though modern society’s impact on the Earth’s environment may not result in an explosion in Ebola, it seems that it will almost certainly drive up rates of these other, far more dread diseases.