How does climate change affect extreme heat and lead to its more frequent occurrence? Record temperatures have been recorded every month since June 2023, and the speed at which these heat waves are being recorded is unprecedented.

Climate change is making heat waves longer, more intense and more frequent. Burning fossil fuels releases greenhouse gases like carbon dioxide, which trap heat in the atmosphere. Higher emissions mean more heat is trapped, which intensifies global warming and leads to more extreme weather events.

Based on 152 studies related to extreme weather conducted by scientists around the world over the past two decades, 93% confirms that human-caused climate change is increasing the likelihood and severity of heat waves.

Heat waves can trigger a chain reaction of harmful impacts. For example, they lead to droughts, fires, poor air quality, water, food and energy shortages, with devastating consequences for communities around the world. In Canada, wildfires burned 7.8 million hectares in 2023 and released 3 billion tonnes of carbon dioxide, contributing to air pollution that has reached as far as Europe and China. The released carbon dioxide can cause further heat waves and create a dangerous feedback loop.

Flooding and heat waves are often linked. High temperatures increase the risk of flooding because warmer air can hold more moisture and dry soil is less able to absorb precipitation. For example, a prolonged heat wave in India and Pakistan in 2022 contributed to devastating flooding in Pakistan and parts of India and Bangladesh.

Moreover, the impacts of extreme heat are uneven. Developing countries and lower-income communities are at greater risk of heat-related health problems or death, due to factors such as geographic location and limited access to air conditioning. According to a 2022 study, lower-income populations are 40% more at risk from heat-related illnesses than wealthier groups. This inequality will worsen as temperatures rise.

Definition and types of heatstroke

Heat waves are long periods of abnormally high temperatures, specifically defined by reference to the average historical temperatures of a given location. If the temperature exceeds the average for at least two days, we call it a heat wave.

A heat dome describes a situation where warm air is trapped under an area of high pressure, creating “domes” of warm air that increase temperatures. A high-pressure system also means low cloud cover, which intensifies the effect of solar radiation.

Impacts of extreme heat

Extreme heat has diverse, complex and uneven impacts on health, food security and the economy. Between 2000 and 2019, there were an estimated 489,000 heat-related deaths per year. Cardiovascular disease is the most common cause, but heat stress can also exacerbate other health problems, increase the risk of accidents and the transmission of infectious diseases. In 2019, heat waves contributed to the loss of 302 billion working hours, an increase of 521 billion hours compared to 2000.

Ongoing heat waves are disrupting agricultural production, reducing agricultural labor capacity, and contributing to food insecurity. Negative impacts on food security have led to increased food prices and reduced access to nutritious resources, disproportionately affecting low-income communities.

Heat waves also negatively affect water supply and quality, at a time when more water is needed for drinking and irrigation.

Government strategies and climate resilience of cities

Various governments have put in place action plans to address the risks associated with heat waves, including warnings of expected temperature extremes and initiatives to protect vulnerable communities. Early warning systems are key to informing the public about survival strategies such as hydration and sun avoidance.

There is an increasing emphasis on preventing and mitigating the impacts of extreme heat before it occurs. A key approach is the appointment of Chief Heat Officers who focus on heat mitigation measures in cities.

Examples of strengthening urban infrastructures to increase resilience to heat waves include creating "cool islands" and "green corridors", expanding green and blue infrastructure, and optimizing buildings and their air conditioning.

In the long term, it is important to reduce greenhouse gas emissions to mitigate the effects of extreme heat. There are also opportunities for economic development by adapting sectors such as transport, construction and agriculture, which can create jobs and support growth. Ultimately, heat waves represent existential threats that require a comprehensive and strategic response. (Co2AI)