The health impacts of a warming world

By Laura Watson

As Europe begins to recover from the COVID-19 pandemic, and potentially lean towards a green recovery, the immediate and longer term impacts of a warming world must be considered. While we learned in a recent blog post about the interaction between climate change and disease, climate change also poses a range of other health threats for a large part of the global population. Most of the information presented below comes from a recent review of climate change and mental health.
 
Physical implications of warming temperatures
Warmer temperatures can have many physiological impacts. It is thought that the optimum temperature for humans is around 22oC, while exposure to higher temperatures can directly impact biochemical levels in the body. For example, differing levels of heat change the amounts of key neurotransmitters, serotonin and dopamine found in the body. High temperatures can also disrupt human temperature regulation mechanisms.
 
Mental implications of warming temperatures
Beyond the physical impacts, warming temperatures can also affect mental health at differing rates and times, causing a variety of impacts. Heat stress, for instance, is typically brought about by heat waves, and is associated with anxiety and mood disorders.
 
In warmer temperatures, people experience higher levels of discomfort, which leads to an increase in aggressiveness and hostile behaviour. Empirical evidence shows that hotter cities experience higher levels of violence than cooler cities, a phenomenon which is likely compounded further by the urban heat island effect. 

However, a caveat must be issued along with these findings, because heat stress and the implications of higher temperatures can be influenced by a wide range of cultural, social, political, and behavioural factors. Another factor which adds to the complexity of investigating the relationship of temperature and mental health is the wide variation in levels of exposure to high temperatures between groups across the world, making it more difficult to assess the relationship between the two.
 
Expansion of areas and people experiencing high temperatures
The decade between 2010-19 experienced exceptionally high temperatures, and the month of May, 2020 was one of the warmest and sunniest on record. As of June 2019, Europe had experienced 5 500-year summers over the course of 15 years (meaning record breaking temperatures were experienced during those years). For a continent not expecting to experience such high temperatures, the implications were devastating. The 2003 heat wave was the most deadly, with 70,000 deaths attributed to the extremely high summer temperatures. Since then, medical services have become more prepared, but high temperatures continue to be dangerous, especially in areas less prepared for them.
 
This is compounded by the urban heat island effect, wherein urban areas are much warmer than their rural surroundings. This is caused by the energy produced by so many people concentrated in a relatively small area, as well as the way urban infrastructure tends to trap heat. People in cities frequently experience higher temperatures than forecasts predict, and night-time temperatures in cities often don’t fall as much as they would be expected to. The urban heat island effect intensifies the impact of increasing heat waves on cities with climate change.
 
Tropical economies (before COVID-19) were growing 20% faster than the rest of the world. This means that more people will be living in areas experiencing high temperatures, at the same time as the temperatures in these regions are rising. Rural to urban migration means that there will be an increased number of people exposed to high temperatures and heat stress.
 
Overall, it seems that climate change has impacts beyond the atmospheric and oceanic systems, and can affect mental and physical health in ways we are only just starting to discover.