This summer, many parts of the world have been breaking heat records one after another. Countries like the United States, Canada, Japan, South Korea, China, and Europe have been experiencing extreme heatwaves, with temperatures reaching or even surpassing 40℃ in some areas.
What exactly is causing this unusually hot summer? Experts believe that it’s not a single factor but a combination of several reasons occurring simultaneously.
According to the latest monitoring data from the National Oceanic and Atmospheric Administration (NOAA) in the United States, the El Niño phenomenon in the equatorial Pacific is continuing to develop and significantly intensify this summer.
El Niño, also known as the “Little Boy” phenomenon, refers to a climate phenomenon where the sea surface temperatures in the eastern equatorial Pacific Ocean remain abnormally warm. It typically occurs every 2 to 7 years and lasts for about 9 to 12 months.
This climate pattern is driving global land and ocean temperatures to be higher than normal on a large scale. When the sea surface temperatures in the equatorial Pacific are unusually warm, a large amount of heat energy is released into the atmosphere, causing further global warming and increasing the likelihood of extreme weather events such as droughts, heatwaves, wildfires, and heavy rainfall.
Scientists predict that this phenomenon will further intensify in the latter half of this year, with far-reaching impacts on global climate patterns. The intensity of El Niño is expected to peak in November to December this year, and the chances of it developing into a super El Niño are gradually increasing, potentially making it the strongest El Niño on record.
Under the influence of a super El Niño, the likelihood of extreme weather events will further increase. Citizens are advised to pay attention to weather warnings and alerts and beware of the potential threats posed by various extreme weather conditions.
In a region where extreme high temperatures persist for several days or even weeks, it is referred to as a “heat dome” or “heatwave,” according to the climate assessment website ClimateCheck.
While “heat dome” is not a standard scientific term, it effectively describes a high-pressure atmospheric system that pushes warm air downwards and traps it for extended periods. These extensive areas of hot air can lead to intolerably high temperatures, devastating wildfires, droughts, and other related issues.
In general, in mid-latitude regions of North America, weather systems typically move from west to east, resulting in a constant interchange of high-pressure and low-pressure systems, cold air, and warm air, leading to changing weather patterns.
Sometimes, the jet stream that controls weather movement weakens or even becomes distorted, stagnant, or fractured. When the jet stream stagnates, high-pressure systems can linger in one area for prolonged periods, making them resistant to movement. When a high-pressure system establishes and remains stagnant within the jet stream, air from high altitudes continuously sinks downward.
Normally, when the ground heats up, the warm air rises, carrying heat to higher altitudes. However, high pressure can suppress the warm air, preventing it from rising and dissipating heat. As a result, heat accumulates near the ground’s surface.
With the ongoing high temperatures, moisture in the soil evaporates rapidly. Under normal circumstances, some solar energy is used to evaporate moisture, which has a cooling effect. But when the land becomes dry, there is hardly any moisture left to evaporate, and more energy directly heats the ground, causing further temperature increases. This creates a feedback cycle: the drier the land becomes → the faster the temperatures rise → even drier conditions → hotter temperatures.
As long as the high-pressure system remains stagnant, the hot air cannot dissipate. The sun continues to heat the ground during the day, and at night, the heat is retained, setting a higher starting point for the next day’s temperatures. Consequently, heat domes can persist for several days or even weeks, resulting in prolonged periods of intense heatwaves.
In densely populated cities, large amounts of concrete, asphalt, and glass buildings absorb heat during the day and slowly release it at night.
As a result, on the same day, urban temperatures are often 2 to 5 degrees higher than in suburban areas, with some major cities possibly differing by over 8 degrees. The urban heat island effect is not a new phenomenon, but when it coincides with factors such as heat domes, the impact is magnified.
The Canadian climate information website Climate Atlas states that many cities are taking measures such as:
● Increasing parks, planting trees, and green roofs.
● Using light-colored or high-reflective materials for roofs and pavements (commonly known as “cool roofs” and “cool pavements”).
● Preserving ventilation corridors in urban planning to improve air circulation.
● Improving building energy efficiency to reduce waste heat generated by air conditioning and other equipment.