We’re only midway through spring, yet searing summer temperatures have already started baking some parts of the world.
Cities like Phoenix and Palm Springs, California, closed in on triple digits in March; Phoenix usually doesn’t reach 100 degrees Fahrenheit until May. This month, hundreds of millions of people across India and Pakistan experienced temperatures as high as 120 degrees Fahrenheit, triggering power outages and protests. The heat has also helped exacerbate conditions for thousands of wildfires in the region.
This is all part of a pattern. Last year, heat waves coursed through Africa and Europe during the spring, setting new temperature records in more than a dozen countries. Mexico experienced a series of heat waves beginning in April. A heatwave in Texas in May sent power demand to a record high for the month.
As global average temperatures climb higher, the frequency and duration of periods of extreme heat are only growing.
Climate change is leading to shorter winters, earlier springs, and earlier arrivals of extreme temperatures. Heat waves that occur early in the warm season, well before summer sets in, can also be the most dangerous.
“These early events can cause more heat-related illnesses and fatalities than later heat waves in June or July, even if temperatures are similar,” Davide Faranda, a climate scientist at the French National Center for Scientific Research studying extreme weather, wrote in an email.
There are several factors behind this. One is acclimatization. When winter ends, people are less used to high temperatures at a physiological level. When ambient temperatures are higher than body temperatures, individuals absorb more heat, which can lead to heart and lung problems, first in vulnerable people, then in everyone. Gradual exposure to heat over time can help people better withstand it, but without this familiarity, an early season heat wave can pack an unexpectedly strong punch.
Humans acclimatize through behavior as well. Drinking water helps limit the dangers of high temperatures, but someone might not be in the habit of staying adequately hydrated in the spring. A person may not recognize that heavy sweating, light headedness, and severe fatigue are symptoms of heat illness.
Even our infrastructure has an influence on this. Many buildings may still be set to heat rather than cooling when the first heat wave of the year sets in. The low availability of air conditioning in the Pacific Northwest contributed to the death toll of a severe heat wave in 2021 that killed at least 868 people.
Early season heat waves may be growing worse.
Along with an international team of researchers, Faranda analyzed the factors behind the recent heat wave across India and Pakistan. The group found that events like the severe heat wave in April 2025 are 4 degrees Celsius warmer over the past three decades than they were in the period between 1950 and 1986.
The recent scorching temperatures also took place at a time when the El Niño-Southern Oscillation, a major driver of global weather variability, was in its neutral phase. In its warm phase, it tends to drive up global temperatures, so seeing this heat wave without this additional boost adds to the evidence that climate change is a major contributor.
Precipitation also appears to be shifting in South Asia, with more spells of severe rainfall followed by drought. And as the planet continues to heat up, these trends will continue.
While many factors are unique about South Asia, other regions of the world are on the same course. The same pattern of more frequent heat waves earlier in the season is also playing out in countries like Indonesia, Malaysia, Thailand, and Vietnam, leading to similar problems.
The US is also facing an increase in the number of heat waves, with warming starting earlier in the year. It’s leading to more complications from extreme heat as well as leading to longer, more intense pollen allergy seasons.
To reduce the dangers of springtime heat, it’s important to pay attention to weather forecasts and prepare accordingly. That means avoiding direct sunlight, proactively staying hydrated, and taking breaks during high temperatures. Ease into the warm weather. It’s also essential to recognize the warning signs of heat-related complications and not to try to push past your limits.
