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A Threat to Ecological Security from Inter-Species Viral Distributions Driven by Climate Change

A scanning electron micrograph shows the Nipah virus (yellow) budding from the surface of a cell.

By Dr. Marc Kodack

Most of the security analysis on climate change effects has been focused on human systems and how people need to mitigate and adapt to those effects. However, these same effects will also create multiple opportunities for humans to become hosts for new pathogens, such as viruses, potentially significantly altering and disrupting both human systems and the ecosystems they are an integral member of (see here). A recently published study in Nature investigating how climate change is contributing to an increase in cross-species viral spread among mammals spotlights the criticality of incorporating ecological security into broader national security analyses.

While modern humans and wildlife have been interacting for several hundred thousand years in selected parts of the world, the vast global changes that have occurred because of increasing concentrations of greenhouse gasses have and will greatly alter these interactions far into the future. In the recent Nature article the researchers modeled the potential interactions among 3,870 mammalian species, including humans, as climate and land use changes (see also here) occur up to 2070. The researchers selected a subset of mammal species based on their biodiversity and the variety of viruses they carry (alternatively see here and here). The models examined the likelihood of climate change creating opportunities for viral sharing through physical contact and interaction that were absent in the past. Implications of these new interactions include effects to wildlife populations as well as local, regional, and global human health. Bats, compared to terrestrial-only species such as ungulates (horses, pigs, deer, zebras, giraffes, antelope) and rodents, have a greater ability to migrate to new areas because of their aerial mobility. Size and position in a food chain also affect mobility.

The study’s authors conclude that most mammal species will cross paths with at least one other mammal species that they have not encountered previously because of changing species distribution. While these changed interactions are global, tropical Africa and Southeast Asia will have higher rates of these new interactions. Of the 10,000 or so known mammalian viruses, new interactions may occur because of viral transfers between hosts that may also result in new viral variants that respond and adapt to their new host environment. New reservoirs of infected hosts may be created.

The scale, scope, and intensity of effects from changes in host viral load are likely to disrupt both existing natural and human systems. For human populations, their higher densities will create “novel viral sharing [opportunities and] will broadly coincide with high population density areas in 2070, especially in the Sahel, the Ethiopian highlands and the Rift Valley, India, eastern China, Indonesia, and the Philippines” (Carlson et al).

The research suggests that there is an increased probability that under climate change, human populations that encounter and interact with wild animals will be exposed to potential new virus loads carried by new hosts. It is unknown what the rate of these interactions will be over the coming decades. It is likely the rate will be uneven across the globe, surging and falling in some areas, whereas in other areas encounters may be rare. However, the consequences of the spread of new viruses as they pass from host-to-host, mutating and adapting along the way, can be globally catastrophic if variants have increased lethality to those infected. So, what are the security consequences?

In a survey of security experts, the respondents identified increased human-wildlife interactions as one of the most significant socio-ecological stressors into the 2030s. One of the socio-ecological stressors is increased interactions between humans and wildlife. Based on the Nature article’s research, these increased interactions bring along the potential for new viruses. The experts thought that the greatest security risk of these human-wildlife interactions was to global health, and more importantly to human insecurity, even when all the other socio-ecological stressors and security outcomes were considered. When bundled with other threats to human insecurity, including climate change, increasing the chances of more viruses moving into human populations degrades those population’s current conditions.

Dr. Marc Kodack is Senior Fellow at the Center for Climate and Security and former Sustainability and Water Program Manager in the Office of the Deputy Assistant Secretary of the Army for Energy and Sustainability.

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