Heat Storms Now Impact 85% of Earth, Reshaping Global Climate Patterns

Over the past six decades, heat waves have transformed from occasional, localized events into vast, persistent heat storms that can span much of the planet for extended periods. The scale and duration of these extreme heat episodes have increased dramatically, reshaping global weather in profound ways.

During the 1960s, the largest heat wave covered roughly 6% of the Earth’s surface, lasting 46 days across the Atlantic Ocean, parts of Latin America, and West Africa. Today, the most significant heat storm has stretched over nearly 85% of the globe, lasting an unprecedented 367 days and reaching as far as polar regions. This means almost every person on Earth has been affected by such extreme heat conditions.

Experts consulted by Reuters, including meteorologists and climate scientists, analyzed hourly temperature data since 1960, covering more than one million global grid points. Their findings led to defining a new term: "heat storm." Unlike traditional heat waves, which are defined as five or more consecutive days of unusually high temperatures, heat storms refer to exceptionally large heat waves that cover at least 1% of the Earth’s surface—about half the size of Canada—at their peak.

Heat storms were a rarity in the 1960s, averaging only five annually, but in the current decade, their frequency has soared to about 102 per year. One recent heat storm caused record-breaking June temperatures across Europe, including 42.7 degrees Celsius (108.9 degrees Fahrenheit) in Bilbao, Spain. The prolonged heat warped steel railroad tracks, led to over 10,000 excess deaths in a single week, and forced zookeepers in Belgium to cool tigers with ice-encased meat.

The largest recorded heat storm, spanning 2023 to 2024, pushed temperatures in the Philippines to 38 degrees Celsius (100.5 degrees Fahrenheit). This extreme heat created severe hardships for students in schools lacking air conditioning. Joel Arrojado, a math teacher in Manila, recounted a distressing incident where a student suffered a spontaneous nosebleed due to the heat, a common health issue during such events.

In the southern United States, the same heat storm aggravated a historic drought in Louisiana, sparking the state's worst wildfire outbreak since World War II, with nearly 600 fires reported in August alone. Two months later, smoke from a marsh fire contributed to a dense "super fog" that caused a massive highway crash involving at least 158 vehicles and resulting in seven fatalities.

Heat storms have also influenced extreme weather elsewhere. In 2023, one such event intensified a Mediterranean cyclone that unleashed heavy rainfall over Libya. The subsequent dam failures near Derna devastated neighborhoods and caused numerous fatalities. Sabreen Blil, a survivor, was seen searching through rubble for her missing family members, highlighting the human toll of these disasters.

During Saudi Arabia’s annual Hajj pilgrimage, the heat storm drove temperatures at Mecca’s Grand Mosque to a staggering 51.8 degrees Celsius (125.2 degrees Fahrenheit), leading to the deaths of over 1,300 pilgrims. At the same time, wildfires in Greece’s Dadia forest, fueled by intense heat, claimed the lives of migrants traveling through the area. Their remains remained untouched for days as even scavenger birds fled the flames.

Researchers emphasize that these far-reaching catastrophes are connected through a single heat storm event. James Renwick, a physical geography professor at New Zealand’s Victoria University of Wellington, described heat storms as causing "major disruption to global civilization," noting that heat-related deaths and resource conflicts are among their grave consequences.

This new classification of heat storms offers a clearer understanding of how rising greenhouse gas emissions are altering the planet’s climate. While scientists track global temperature increases—such as the 1.47 degrees Celsius (2.6 degrees Fahrenheit) rise above pre-industrial levels projected for 2025—this data often feels abstract to the public. Heat waves, known by terms like "ola de calor" in Spanish or "mawjat hararia" in Arabic, provide a more tangible way for people to grasp climate impacts.

However, definitions of heat waves vary globally. The U.S. National Weather Service identifies a heat wave as at least two days of unusually hot weather, while countries like Australia, France, Spain, and the U.K. set the minimum at three days. Temperature thresholds also differ based on local climate norms, so a heat wave in Anchorage, Alaska, involves much lower temperatures than in Kuwait City.

To overcome these inconsistencies, Reuters developed a method using historical temperature data from 1961 to 1990 for over one million global locations. A heat wave occurs when daily high temperatures exceed the 90th percentile of this historical range for five consecutive days. This definition applies year-round and adjusts to local climate conditions. For example, a July heat wave in Istanbul requires five days above 25.6 degrees Celsius (78.1 degrees Fahrenheit), whereas in Phoenix, Arizona, it must be above 40.3 degrees Celsius (104.5 degrees Fahrenheit).

Mapping adjacent grid points experiencing heat waves allowed identification of vast, connected areas of extreme heat, which Reuters labels heat storms when covering 1% or more of the Earth’s surface. This approach provides a precise, global perspective on how heat extremes have intensified, offering insights into the increasing risks posed by climate change.