Rising temperatures and subsequent changes to the climate will have a wide range of negative human health impacts, including the spread of infectious diseases. In part one of this series, we looked at how the unsustainable dynamic between humans and nature is increasing the probability of diseases emerging. Here we will assess how changing climatic conditions will exacerbate this phenomenon, as well as how environmental conditions will become increasingly favourable for infectious diseases to spread.
As with other physical climate risks, chronic or acute changes in the climate can act as a threat multiplier for infectious diseases. This gives cause for concern, with the total number of people exposed to infectious diseases projected to increase by 453-900 million by 2080, more than half of which will be accounted for by Europe. The chronic or long-term changes to the climate that are most relevant are changes in temperature, humidity and precipitation. Each of these has a positive, non-linear relationship with the spread of infectious diseases.
The Intergovernmental Panel on Climate Change (IPCC) projects that these changes will have an impact on the transmission intensity and seasonality of certain infectious diseases. However, it is difficult to draw simple causal relationships between these variables and the spread of disease. More research is required to better understand the complete set of dynamics. Furthermore, diseases may not spread in the same way due to the different vectors involved.
Vectors, particularly mosquitoes, are well adapted to warmer climates, and sensitive to small shifts in temperature. An increase in temperatures, therefore, will expand the range over which they can survive and transmit diseases such as malaria and dengue fever. According to The Lancet, a medical journal, nine of the 10 years that were most advantageous for the spread of dengue have occurred since 2000. Similarly, taking a baseline from 1950, the suitability for malaria has increased by 29.9%.
Droughts and floods, which are likely to increase in severity and frequency as the climate breaks down, will also impact disease patterns. The high levels of evaporation and demand for water during droughts increase the likelihood of the remaining water turning stagnant, forming ideal breeding grounds for mosquitoes and other vectors.
Conversely, studies in Panama have demonstrated how rat populations, another common disease vector, sharply increase following heavy rainfall and flooding. Also, there will be secondary impacts from these extreme weather events, such as changes in farmed land and increasing poverty, which will exacerbate societal vulnerabilities to infectious diseases. Shifting agricultural zones, following a decrease in productivity in many areas, will drive further interactions between humans and animals, as discussed in our previous article.
Uncertainty remains around when the coronavirus pandemic will begin to subside. When it does, it is critical that the inevitable economic stimulus has climate mitigation, adaptation and conservation at its heart. In this way, $26 trillion of economic benefits could be realised by 2030, while mitigating the impacts on health and society in the long term. Overdue infrastructure spending will certainly be a part of this, allowing for an acceleration in transitioning transport and energy systems.
However, it is important that governments reserve a portion of these stimulus packages for investing in research and development in the sectors that are more difficult to decarbonise. The Energy Transitions Commission, a think tank, has done an excellent job of drawing attention to the decarbonisation options for many of these ‘hard-to-abate’ sectors. The one sector that remains consistently overlooked is agriculture.
One option, as proposed by the Breakthrough Institute, is to increase the funding of research into alternative proteins. This would help to mitigate the impacts of the climate crisis, as the agricultural sector accounts for around 24% of global greenhouse gas emissions. At the same time, it would reduce the need to continue clearing virgin land for agriculture, which is a key driver of biodiversity loss and the emergence of infectious diseases.
As we will explore in the next few articles in this series, an effective way to mitigate climate breakdown is to reduce our consumption of animal proteins, as the rearing of animals uses land inefficiently and produces a considerable amount of greenhouse gas emissions, whilst also increasing the risk of antimicrobial resistance.