مرحباً بكم في الأمم المتحدة 
A Hippocratic oath for the coming generations
Climate change is the biggest health challenge in the world today. It poses a steadily increasing direct and indirect threat to future generations.
Humans are facing unprecedented challenges, first and foremost related to climate change, nature loss and embedded in this also issues related to health and food security. The Lancet Countdown on health and climate change claims that ‘climate change is the greatest global health threat facing the world in the 21st century, but it is also the greatest opportunity to redefine the social and environmental determinants of health’.
The recent sixth assessment report from the Intergovernmental Panel on Climate Change (IPCC) states that the world is now hotter than it has been for 125 000 years, and current CO2 concentrations are the highest for two million years. The current emission pathway indicates a temperature increase of 3oC by the year 2100. It is not known what extremes await us, even with the 2oC increase that the more optimistic estimates suggest. At the current rate, the increase will exceed 1.5oC in a couple of decades. Even the most conservative scenarios consider a temperature increase of 2oC to be quite likely by the year 2050 – with the current level of emissions. As expected, the report also points to not only a likely increase in the extreme events we are already seeing, but also suggests that these will become more widespread: floods that happened every 1000 years will be seen every 100 years, and more areas will be exposed to them.
Ecosystems have served us extraordinarily well so far with their net carbon capture. In fact, more than half of our emissions are absorbed by ecosystem sequestration. If the ability of nature to absorb CO2 is weakened or, in the worst case, reversed, we will really have problems. One of the most frightening topics in the IPCC report is the risk of a reversal in the net terrestrial and marine CO2 uptake to a net emission to the atmosphere. We are already seeing the outlines of this in the reduced ability for CO2 uptake in tropical forests, CO2 emissions (in the worst case also methane (CH4)) from increased thawing of permafrost, wildfires and warmer and more acidic oceans. Such self-reinforcing feedback loops can lead to climatic tipping points. It is not therefore ‘only’ a matter of CO2 and the climate, but also about the loss of nature and the resulting weakening of ecosystem services such as CO2 uptake, carbon storage and flood control.
Nothing is as potentially threatening to public health as climate change. It has already directly claimed numerous victims as a result of flooding, fires and extreme heatwaves, but the IPCC report warns this is just a precursor of what is to come. The indirect effects will be even greater because the disease, water and food shortages, poorer sanitation and migration resulting from the deteriorating living conditions, extreme heat, fires and rising sea levels will in themselves constitute major social and health challenges. The term ‘climate refugee’ has already been established, and these refugees could stem from different regions for different reasons. The European Commission describes this clearly in its report Proposed Mission: A Climate Resilient Europe: ‘The COVID-19 pandemic has taught a lesson about how closely environmental, societal and human health are connected. What we have lived through and still will is a mild foretaste of the shocks that climate change may and will cause in the future.’
Apart from the severe consequences of climate disasters like floods, landslides, fires, death from heat stroke is also becoming an increasingly relevant problem, even in areas where this has never previously been seen. For example, compare the extreme temperatures up to 50°C that were recorded in Canada in early summer and subsequently on the west coast of the United States, and the record temperatures in Europe in late summer. We have already seen heatwaves that resulted in tens of thousands of deaths, and ‘wet-bulb’ temperatures’ in excess of 35°C are expected to become more frequent and widespread, leading to an exponential rise in deaths from heat stroke.
This is just one of the many factors included in the calculations of which parts of the planet will become uninhabitable under different climate scenarios. Although humans inhabits most parts of the planet with climatic extremes, the human climate niche is relatively narrow at the hot end in terms of food supply, water and temperature tolerance. It is estimated that 1–3 billion people may end up outside the habitable niche in the course of 50 years. Put bluntly, the choice is between relocation, where this is possible, and a high risk of death from heat stroke. It is also worth remembering that extreme temperatures, droughts, fires and floods also mean enormous losses for the planet’s other forms of life.
Loss of nature and climate change are closely linked, and encroachment on nature also increases the risk of pandemics. A comprehensive analysis of 6800 ecosystems on six continents shows the mechanisms that link the destruction of nature and pandemics. Ebola, AIDS and rabies, and a host of other diseases, such as MERS, SARS, influenza A (H1 N1) and the Nipah virus, can all be traced back to close contact between humans and animals. Nevertheless, a coronavirus pandemic was needed before the problem was taken seriously.
There has also been a marked increase in the number of zoonotic diseases in recent years. This is largely because humans and domestic animals are encroaching on new territory, we are chopping down existing forests and fragmenting ecosystems, which means we are having more close contact with wild animals. This promotes the spread of viruses, bacteria and other pathogens to humans, either directly or via domestic animals.
Another reason for the increase in diseases is that reduced biodiversity seems to favour a few chosen species with a particularly high potential for the spread of infection, such as rats, bats and some primates. In particular, bat populations are reservoirs for viruses that cause Ebola, Nipah virus infection, SARS – and now COVID-19 – in humans. When their natural habitats are destroyed, they are forced to seek food where humans and livestock live. This increases the risk of infection. Population numbers and consumption are common drivers of climate change and loss of nature. These problems require a systematic approach, and the challenges must also be addressed through education.
The impact of climate change on our health not only relates to the direct and indirect ramifications of climate change itself, but also the psychological effects, such as anxiety. The Greta Thunberg generation is questioning whether there is a future when the outlook seems so bleak. This raises the issue of how risk should be communicated. There is no simple recipe for this, other than following the research, as summarised in the IPCC’s reports. The situation is serious. The world and humanity will still exist, but undoubtedly at the growing expense of our physical and mental well-being. We need hope for the future, backed up with action. The window to act is shrinking, while the impact on the future is worsening. We need a policy with a thousand-year perspective – and a Hippocratic oath for those yet to be born.
By Dag O. Hessen, Professor in Bioscience at the University of Oslo and head of the Centre for Biogeochemistry in the Anthropocene (CBA) / d.o.hessen@mn.uio.no
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