Pandemics and the climate crisis — understanding their connection, and what it means for human identity

Even those who are unfamiliar with Spider-man are probably familiar with the advice given to him: “With great power comes great responsibility.” Although we know that we carry responsibility, we can feel quite powerless in the face of the two major crises the world currently faces.

We are still in the middle of a global pandemic, and at the same time are starting to experience the consequences of global warming. For almost two years now, we have witnessed disturbing footage of overburdened intensive care units on the news and intensely followed numbers on incidence or death rate as well as new guidelines and vaccination developments. At the same time, we have seen images of wildfires in the United States and Canada that were out of control for weeks, dramatic video footage of the floods in Japan and Europe, and of the devastation of the Atlantic hurricane Ida.

While some Christians interpret this double threat as a clear sign of the end-times, others lean back and disregard it as an unfortunate coincidence, a time that also shall pass. Sadly, both reactions can result in personal as well as communal passivity. Therefore, I want to ask: Is there something about their connection that we, as Christians, need to understand? And, if so, what should that understanding prompt us to do?

Where do pandemics come from?

As a virologist, I am more familiar with viruses than the climate crisis. So, let’s go back to some of the latest newly emerging infectious diseases in humans and think about where they came from.

Within the last twenty years, we had to face three major outbreaks of coronaviruses in the human population. Coronaviruses, like many other viruses, are known also to circulate in other species and to have a reservoir in bats. If a virus crosses the species barrier, it infects an immunologically naïve human and can in this way quickly cause a widespread outbreak. Because bats and humans are quite different, it usually needs an intermediate host for the virus to successfully adapt to the human cell. For the SARS coronavirus in 2003, the intermediate host was probably a Civet cat; for the 2013 MERS coronavirus, the intermediate host was a camel; and for SARS-CoV-2, we are not sure yet since it could be detected in a range of different mammals. But in the end, all three viruses jumped species through direct interactions of humans with these animals and were then transmitted from human to human.

Similar scenarios are true for other epidemics and pandemics. Newly emerging influenza viruses have been transmitted to humans through a range of different species. In 2009 an influenza H1N1 virus crossed the species from swine to humans. This virus is now known as the “swine flu”. A range of avian influenza viruses also crossed species to humans in the last twenty years — in 2002, 2013, 2014, and 2018. Similarly, for Ebola viruses, we know that there is a reservoir in bats and that, every once in a while, the virus can be transmitted either directly or indirectly to humans. Indirect transmission is increasingly likely through contact with other infected animals, who picked up infected material dropped by bats, or through the consumption of bushmeat.

Overall, there were a significant number of newly identified emerging infections in the last thirty years or instances where a disease has spread to a new area. It is estimated that approximately 60 per cent of all infectious diseases and 75 per cent of emerging infectious diseases in humans are caused by Zoonoses — or cases in which viruses jumped species from their animal reservoirs and adapted to our cell machinery and immune system.

Pandemics and climate change

What does all this have to do with climate change? I want to argue that the underlying causes of pandemics and climate change are the same. Industrialisation, globalisation, and an increase in the world’s population are putting pressure on our climate and the ecosystems around us. While it is for other experts who study the changes in the world’s climate to explain how a globalised world puts pressure on the climate, virologists can also see the consequences. Consider the following examples.

Reduced species diversity within ecosystems increases the chance for viruses to quickly adapt to a new host. The higher the diversity, the more limited viruses are in this ability.

Destroying ecosystems forces animals into different habitats — and their viruses with them. Deforestation and exploitation of nature will therefore come with an increased risk for viruses to cross the species barrier.

The way we organise our food production increases the risk of virus adaptation and transmission. We need to think afresh about our animal markets or animal husbandry.

Over the last two years, we have talked a lot about biological factors that influence the transmission of viruses — such as the acquisition of specific mutations. We also talked about human social and behavioural factors, including treatment options, vaccination, or social distancing measures. The bottom line is that both pandemics and climate change are profoundly affected by human behaviour and decision making.

Global warming and the spread of viruses

Interestingly, research has also shown that the spread of infectious diseases is not only determined by biological as well as human social and behavioural factors, but also by environmental factors. This means, that global warming will affect the spread of viruses. One reason is that the climate crisis will have an impact on the habitats of different species and their geographic distribution.

An obvious example is the case of arboviruses. These viruses can replicate efficiently in different hosts and use these so-called vectors as a mode of transportation —the best known instances of which are mosquitoes, ticks, sandflies, or biting midges. There are more than 500 known arboviruses, of which around 100 can cause disease in humans and several types of mosquitoes are known to be able to spread them. If these vectors migrate to new areas, this will necessarily change where a particular virus spreads. Famous examples of relevant human pathogenic viruses include Dengue virus, Zika virus, West Nile virus, and Chikungunya virus.

Researchers are trying to forecast the implications of climate change for these viruses as a key component of public health preparedness. Changing temperatures will produce different patterns of shifts under climate change for different types of mosquitos and the risk of transmission will increase substantially for most of Europe.

Global warming and the ocean

Global warming will not only affect the geographic distribution of different species but also the way different ecosystems work. We know that the ocean is a major player in the climate. The oceans comprise more than 70 per cent of the surface of the Earth and have the capacity to store more than one thousand times the heat compared with the atmosphere. They serve as the main reservoir and distributor of heat and salt, regulate and modulate evaporation and precipitation, and contribute to the formation, distribution, and melting of sea ice. Furthermore, the oceans are the primary storage medium for, and absorb large quantities of, the greenhouse gas CO₂ (around 37,000 gigatonnes).

Therefore, oceans are not only affected by the climate, they are also a key player that regulates the climate. Hence, climate change will have a range of consequences for marine ecosystems, and through the ocean, will affect all other ecosystems as well.

Yet surprisingly little is known about how climate change will affect viruses in the oceans. Viruses do not only infect mammals and mosquitos, but all species on this planet — including bacteria. In the ocean, viruses are about fifteen-fold more abundant than archaea and bacteria, equivalent to the carbon in around 75 million blue whales. They are thought to play important roles in the availability and cycling of nutrients and influence community structure. They are also an important provider for gene transfer, the evolution of aquatic organisms, and (re)packaging of genetic information. Cyanobacteria produce approximately 50 per cent of the Earth’s oxygen. Interestingly, they are often infected by viruses, many of which contain genes that encode core photosynthetic proteins, and that are expressed and have an evolutionary history that is distinct from that of their hosts. In this way, viruses might make an essential contribution to the vital production of oxygen.

Climate change will directly affect virus hosts in the ocean in various ways, and we currently cannot estimate the consequences this will have on virus abundance and diversity, or on the functions they fulfil. Marine viruses could have a wide range of effects on climate change, but we can still only inadequately estimate the extent. Whatever the effect is, it will probably also differ between oceanic regions or latitudes, and might even be contrasting. Viruses are not usually considered in models concerning the effects of climate change and we cannot yet predict whether the viruses will exacerbate or smooth the effect of climate change on marine ecosystems. A better understanding of the biology of viruses within the oceans would enhance our ability to predict and adapt to the consequences of such changes.

The viruses that shaped the world

I hope these examples have shown how closely pandemics and the current climate crisis are connected. Since viruses can infect every single species on this planet, and even cross species barriers, they are a link between all ecosystems. And this means they are also linking us to all ecosystems. The importance of this is reflected in the increasing efforts of the One Health movement. But viruses have done more. They have shaped the world in which we live, and they have also shaped us.

Viruses have been around since the beginning. Starting as replicative elements (and therefore virus precursors) they might even have been a prerequisite to life. In their co-evolution with their host, they will have shaped the way cellular systems work and developed. They have put pressure on all cellular processes and provided new genetic material. One study estimates that viruses have driven close to 30 per cent of all adaptive amino acid changes in the part of the human proteome conserved within mammals.

Many historic infections throughout the course of evolution remained with us because some virus families can integrate their genetic material into our genomes. The viruses that integrate into our germline will be inherited by future generations. Sequencing the human genome revealed that over 40 per cent of mammalian genomes consist of these so-called retroelements. In some cases, we know that our cells recycled integrated genetic material from viruses that is now involved in important tasks. Proteins that are coded by these genes can be used to fulfil important functions. Famous examples are proteins like syncytin-1, which plays a pivotal role in the formation and function of the placenta, or Rag1/2 proteins which are important for the development of an adaptive immune response. Since viruses also carry many regulatory sequences, it is thought that they can potentially be used to coordinate networks of responses within cells.

Overall, viruses teach us that not only pandemics and global warming are linked, but that all ecosystems are connected through viruses, and that viruses are a major force that shaped the way our world works today.

“Intimate interconnectedness”

There are, of course, many more things to learn about viruses, and much more that still needs discovering. But what do we make of what we already know? The mechanisms of pandemics and global warming point us to several profound biological and theological truths.

First, as humans, we are part of a complex and interconnected world. We are not separated from what is happening on our planet, but just as exposed and involved as every other species. Humans are part of creation, but yet somehow responsible for stewarding it.

Second, both biology and theology show that our behaviour is not without consequences and that our decisions matter. We are not only given responsibility, but also understanding of the biological processes with which we are interacting. We can consciously choose to study them in more depth and gain a better understanding.

Third, both theology and biology point us to a healthy humility in which we not only understand our responsibilities, but also our limitations. Both biology and theology warn us to not overestimate our capabilities. The reality is that the world is complex and that there is much more to be discovered. True humility in both biology and theology means that we need to accept that there is a difference between knowledge and wisdom, and that, despite having a large amount of knowledge, there is still a great deal that we cannot assess.

Fourth, we share a communal history with all other species, yet we are all different.

In many ways both the climate crisis and the current pandemic call on our responsibility. This can feel incredibly demanding, perhaps even overwhelming. At the same time, both global warming and emerging virus infections can be a reminder of our true identity as created beings in need of wisdom and salvation. We can change the world with small decisions every day. We can also allow our hearts to be changed when we ponder the implications and gifts of a complex world and the evolutionary process.

How could this change our perception of our human identity or the origin and definition of life in the first place? And would a change in heart and understanding of our human identity even help us steward ecosystems? Forty years ago, John B. Cobb wrote:

Christian theology as a whole suggests, in principle, a global perspective. That is, Christians recognize that they are called to consider the totality of God’s creation and especially the planet earth. But as long as the intimate interconnectedness of the parts is not deeply realized, the habit of identifying and solving problems in terms of very limited contexts prevails.

Viruses are offering us deep insights into our interconnectedness with the world in which we live, and God is gifting us with this knowledge and trusting us with the responsibility that comes with it. How should we tackle both pandemics and the climate crisis from this perspective? How will this change our actions and our prayers? How will this shape the way we engage with biology and theology — as a scientist? as a theologian? as layperson?

Dr Mirjam Schilling is a virologist at the University of Oxford and a DPhil student in theology (Science and Religion) studying the theological aspects of viruses under Alister McGrath.