With the COP26 summit taking place over the next 12 days, climate change is currently at the forefront of discussions around the globe.

Although these summits take place every year, many experts believe this year’s COP has a unique urgency. Six years on from the Paris Agreement, world leaders, negotiators, government representatives, businesses and campaigners are coming together to create an updated plan of how to limit global warming by 1.5 degrees.

Slowing down climate change by phasing out coal, curtailing deforestation, switching to electric vehicles and investing in renewable energy is vital for a plethora of reasons. Arguably, the most important of which is limiting negative health outcomes.

Climate change is the biggest health threat facing humanity

Climate change and global health and inextricably linked, in fact, according to the World Health Organization (WHO), climate change is the biggest health threat facing humanity.

This is because climate change causes rising temperatures, rising sea levels, extreme weather and increasing carbon dioxide levels, all of which can have an effect on our health.

Previous studies have documented these health impacts, including an increase in infectious diseases, respiratory disorders, heat-related morbidity and mortality, undernutrition due to food insecurity, and adverse health outcomes due to increased socio-political tension and conflicts.

In fact, climate change is expected to cause approximately 250,000 additional deaths per year, which are disproportionately felt by the most vulnerable and disadvantaged in society. This includes ethnic minorities, poor communities, older populations, and those with underlying health conditions.

Warmer weather increases heat-related diseases

A study recently published in the Lancet Regional Health – Americas journal highlights how rising temperatures threaten our health. The study found that 7.4 per cent of all hospitalisations for renal disease can be attributed to an increase in global temperature. In Brazil, where the study was focused, this equated to more than 202,000 cases of kidney disease between 2000 and 2015.

The researchers looked at more than 2.7 million hospitalisations for renal diseases recorded during the 15-year study period and found that for every 1°C increase in daily mean temperature, there is an almost one per cent increase in renal disease, with those most impacted being women, children under the age of four and those aged 80 and over.

Heat waves can also have serious health effects on older populations and those with underlying health conditions. This was seen during the 2003 heatwave in Europe, which claimed approximately 35,000 lives according to the United Nations (UN).

Poor air quality is associated with respiratory problems

As average temperatures rise across the globe, air quality is to suffer. Many areas across the globe will see increased concentrations of ozone and particulate matter which are associated with various health problems, including diminished lung function, increased hospital admissions and A&E visits for asthma, and premature deaths.

Rising temperatures also cause longer and stronger pollen seasons which can trigger asthma attacks and allergies, as well as cause frequent droughts that can lead to wildfires, releasing dangerous pollutants into the air.

Young children, people with asthma and respiratory conditions, older adults and people with compromised immune systems are more at risk of being harmed, with scientists estimating that additional deaths due to air pollution could range from 1,000 to 4,300 nationally per year by 2050.

Climate change threatens food security

Global warming can affect food production as crop yields decline due to changes in rainfall, severe weather events (such as droughts) and increasing competition from weeds and pests.

Livestock and fish production are also expected to decline, pushing up prices and therefore restricting the number of people who can access such products. The Centers for Disease Control and Prevention (CDC) predict that this will cause people to turn to nutrient-poor but calorie-rich foods to avoid enduring hunger, “with consequences ranging from micronutrient malnutrition to obesity.”

Food quality, or the nutritional value of some foods, is also projected to decline. This is because elevated atmospheric carbon dioxide causes protein levels to deplete in many crops, such as barley, sorghum, and soy. Furthermore, if soil nitrogen levels drop then we will see reduced levels of nutrients in some crops including calcium, iron, zinc, vitamins and sugars.

Farmers are also expected to use more herbicides and pesticides because of increased growth of pests and weeds, meaning farmers, farmworkers and consumers will all be increasingly exposed to these substances, which can be toxic.

Diarrheal diseases are more common when temperatures are higher

Those living in poorer countries are also particularly susceptible to diarrheal disease, caused by exposure to pathogens in water and food. Air and water temperatures, precipitation patterns, extreme rainfall events, and seasonal variations (all caused by climate change) are all known to affect disease transmission.

In general, diarrheal diseases are more common when temperatures are higher, and have also been found to occur more frequently in conjunction with both unusually high and low precipitation.

Children and the elderly are most at risk of serious adverse outcomes, and those exposed to inadequately or untreated groundwater (usually in poorer regions of the globe) will be among those most affected.

Extreme weather events can cause mental health problems 

Climate change not only has an effect on physical health, but can also impact mental health. For example, extreme weather events (such as hurricanes, floods and heatwaves) have been known to induce mental health problems. This was demonstrated in research following Hurricane Katrina, which found high levels of anxiety and post-traumatic stress disorder among people affected.

Additionally, some studies suggest that patients with mental health problems are particularly susceptible to heat, with research finding that suicide rates rise with high temperatures. This suggests potential impacts from climate change on depression and other mental illnesses.

Furthermore, patients with severe mental illness, such as schizophrenia, are at risk during hot weather because their medication can interfere with temperature regulation or even directly cause hyperthermia.

People must "fully understand" the connection between the environment and their own health

Although it remains difficult to accurately estimate the scale and impact of many climate-sensitive health risks, it is clear that the effects of climate change on health are far-reaching and complex.

Vulnerable populations such as ethnic minorities, poor communities, older populations, and those with underlying health conditions are particularly at risk from these adverse health effects, and unless action is urgently taken, these people will remain especially vulnerable to the effects of climate change.

However, there is hope that the COP26 summit will stimulate pertinent discussions about the link between global warming and health and bring about tangible change. 

As Dr Maria Neira, Director of Public Health, Environmental and Social Determinants of Health at WHO, said: "The moment people fully understand the connection between our environment and their own health today, not just the future generations, and we put it in a positive light, I think we can move mountains."