CONTEXT

• Global warming is causing temperatures across the globe to rise significantly enough to cause disruptions
• Increase in instances of Heat waves are occurring with greater frequency and are lasting longer than ever before
• While humans have adapted and acclimatised themselves to several variations in climate, there is believed to be a limit beyond which our bodies cannot process this change

HOW DOES HUMAN BODY TACKLE HEAT?

• Human body responds to excessive heat primarily by redistributing blood flow toward the skin so heat can transfer out of the body and into the environment through sweat which evaporates on the skin, bringing body temperature down – BLOOD FLOW COOLING METHOD
• The cooling method is important for young children
• As long as the air temperature is cooler than the body’s temperature, heat dissipates through the skin to the outside environment
• When temperatures rise, the brain regulates these physiological responses, with additional input from temperature-sensitive nerve cells in the skin and throughout the body
• Cells also produce heat shock proteins, which act as “chaperones” that stabilise the structure of other proteins that high temperatures could damage
• Every cell in the body contains heat shock proteins, protecting a variety of other proteins that are critical to life, including hemoglobin, which carries oxygen to our cells
• Over short periods of time, heat shock proteins are effective and helpful in regulating body temperature, but when temperatures stay too high for too long, they lose their ability to function, and the proteins they protect start to break down – higher susceptibility to infections and a decreased response to vaccines, only a couple of the cascade of reactions that can occur as a result of the breaking down of proteins

HOW DOES HEAT IMPACT HUMANS?

Brain 

• Hypothalamus acts as a thermostat for the entire body, sensing temperatures and reacting to keep core temperatures within a healthy range
• Continuous, high temperatures prevent the hypothalamus from shutting off these cooling responses
• When the heat shock proteins break down, the body identifies them as invaders and sends out immune cells to fight them, thus keeping them from their main task of fighting infections

Skin and Gut 

• In response to heat, pores in the skin open to allow more sweat to pass through and evaporate, increasing the body’s ability to cool itself
• Lining of the gut can become leaky allowing bacteria to pass through to other parts of the body – can increase the likelihood that harmful bacteria and toxins will reach the body’s vital organs via the circulatory system

Heart and Other Muscles 

Heart rate increases to send more blood to the skin, releasing the body’s core heat into the environment – Consequently, less blood is sent to the muscles, which can constrain muscle growth, cause muscle fibers to break down, and contribute to kidney dysfunction

Dehydration 

• Not having enough water in the system thickens the blood, which can lead to increased blood clotting and heart failure from blockages in the arteries
• When sustained over time, all these responses can lead to what is known as “heat stress.”
• Body begins to break down and critical functions shut down, increasing the likelihood of damage to the heart, lungs, and kidneys as well as the risk of heat-related death

EFFECTS ON PREGNANT WOMEN AND CHILDREN

In pregnant women

• Reduced blood flow in the placenta, dehydration, and inflammation, which can trigger preterm birth
• There is evidence that during times of high temperatures, there are increased rates of stillbirth, as well as more premature and lower birth weight babies, again, linked to a greater risk of a range of poor outcomes later in life, including impaired cognition, reduced growth, and chronic health issues such as cardiovascular disease and diabetes in adulthood

In children

• Fledgling ability to achieve homeostasis
• Disrupt development through three distinct pathways:

Learning loss 

• Slower cognitive function and reduced concentration ability
• Effects on the brain can produce slower reaction times and an inability to focus and can have lasting effects on learning outcomes
• Hotter school days two, three, and even four years prior to a test correlate to lower scores

Sleep quality 

Evidence shows associations between less sleep in infancy and childhood obesity, and sleep habits in childhood may impact weight well into adulthood

Mental and behavioural health 

• Children’s brains and bodies are developing rapidly and are highly sensitive to their experiences, early childhood is a period where threats to well-being can have long-lasting effects on mental health
• Brain detects extreme heat as a threat to well-being, which activates the stress response system

NOTE

While heat affects everyone, the paper highlights how it also amplifies the effects of systemic inequities in housing, neighbourhood density, community infrastructure, and economic opportunity, contributing to an unequal burden of dangerous conditions for families from marginalised groups and with lower incomes.

TACKLING EXTREME HEAT

• Address the root causes — and inequality more broadly — will boost the impact of efforts to mitigate the effects of extreme heat on children
• Recommend policies that target emissions, immediate action to reduce harm from heat events, and adapting infrastructure to be better placed to handle the increase in heat
• Improve structural cooling options in buildings, including greening campaigns, installing air conditioning and other cooling mechanisms; providing accessible links to the power grid; and developing proper heat plans