Heat waves are periods of unusually high temperatures that persist for several days or longer, often accompanied by elevated humidity. These events feature temperatures significantly above average for a specific region during that time of year. While heat waves are natural occurrences within Earth’s climate system, their frequency, intensity, and duration have increased in many parts of the world.
Atmospheric Conditions
Heat waves frequently form under the influence of persistent high-pressure systems, often referred to as “heat domes.” These large atmospheric masses of sinking air create stable conditions that trap warm air near the surface. As air within the high-pressure system descends, it compresses and warms further, similar to how a bicycle pump heats up when used. This process, known as adiabatic heating, contributes to the extreme temperatures observed during a heat wave.
Clear skies are another feature associated with heat domes. The absence of clouds allows maximum incoming solar radiation to reach the Earth’s surface, which then absorbs this energy and heats up. Light or stagnant winds within these high-pressure zones prevent the dispersal of warm air, allowing it to accumulate and linger. This combination of sinking, warming air, unimpeded solar radiation, and minimal air movement traps heat, leading to prolonged extreme temperatures.
Climate Change’s Influence
Human-induced climate change plays a significant role in altering the characteristics of heat waves globally. The increased concentration of greenhouse gases, such as carbon dioxide and methane, in Earth’s atmosphere traps more heat, leading to a rise in average global temperatures. This warming establishes a higher baseline temperature from which heat waves develop, meaning typical weather patterns can now result in more extreme heat events.
Elevated baseline temperatures contribute to heat waves being more frequent, lasting longer, and reaching higher peak temperatures than they would in a cooler climate. Climate change can also influence large-scale atmospheric circulation patterns, potentially making the high-pressure systems that cause heat domes more persistent or intense. These alterations in atmospheric dynamics can exacerbate conditions favorable for the formation and longevity of heat waves.
Local Contributing Factors
Specific local environmental conditions can intensify heat waves beyond broader atmospheric and climatic influences. The urban heat island effect is a prominent example, where metropolitan areas experience higher temperatures than surrounding rural regions. This occurs because urban surfaces like asphalt roads and concrete buildings absorb and retain more solar radiation than natural landscapes. These dark, impervious materials release stored heat slowly throughout the night, preventing the urban environment from cooling effectively.
A lack of green spaces, such as parks and trees, in cities also contributes to higher temperatures. Green vegetation provides evaporative cooling through transpiration, which helps dissipate heat from the surrounding air. The absence of these natural cooling mechanisms, coupled with waste heat from human activities like air conditioning and vehicle exhaust, further elevates urban temperatures during heat waves. Topography can also play a role, as valleys or basins can trap warm air, preventing it from mixing with cooler air above. Changes in land use, such as deforestation, can reduce regional evaporative cooling, making an area more susceptible to extreme heat.