Longest Heatwaves Of The Last Century
It will be 102°F in Phoenix this week. Historically, the average temperature this time of year is around 70°F. This kind of sharp deviation is no longer an edge case.
In 2024, Phoenix recorded 70 days at or above 110°F. In central Australia, conditions are similarly extreme. In India, thermometers in major cities have reached 120°F on some days — a danger compounded by severe air pollution. According to Prevention Web, Delhi experienced its most extreme heatwave on record in 2024, with a peak temperature potentially reaching 52.9°C (127°F), though India’s Meteorological Department has questioned that figure.
Extreme heat can kill quickly. Once the internal body temperature climbs above 104°F — which can happen within 10 to 20 minutes of exposure — the situation becomes life-threatening, according to CNN. The WHO estimates that approximately 489,000 heat-related deaths occurred annually between 2000 and 2019, and the world has only grown hotter since.
Climate Crisis 247 examined the longest heatwaves of the past 100 years, drawing on data from Weather.gov dating back to 1869, as well as sources including Geographical, Yale Climate Connections, History, World Energy Data, Live Science. To qualify, a heatwave had to consist of consecutive days with maximum temperatures exceeding 100°F, concentrated within a single city, region, or defined geographic area such as Death Valley. Even a single day below that threshold disqualified a streak.
These are the seven periods of the longest heatwaves in the last century (we included dates as far back as 1913):
Marble Bar, Western Australia (1923–1924): 160 consecutive days above 100°F, from October 31, 1923, to April 7, 1924. Most records recognize this as the world’s longest such streak.
Mecca, Saudi Arabia (2010): 227 consecutive days above 100°F, from March 31 to November 12, 2010.
Phoenix, Arizona, USA (2024): 113 consecutive days with highs above 100°F. The previous city record was 76 days, set in 1993. Phoenix has grown progressively hotter — just two years prior, the southwestern US was enduring what NPR described as its driest period in at least 1,200 years.
Death Valley, California, USA (1917): 40 consecutive days at or above 120°F, from July 9 to August 17, 1917. Death Valley also holds the record for the hottest single day ever recorded: 134°F on July 10, 1913.
Phoenix, Arizona, USA (2023): 31 consecutive days with highs at or above 110°F in July — a city record for that threshold.
Russia (2010): Approximately six weeks of severe heat across western Russia, including Moscow, from late June to mid-August, with at least 31 days exceeding 100°F. According to Oxford researchers, the event caused an estimated 55,000 deaths, a 25% drop in annual crop production, and more than $15 billion in economic losses.
United Kingdom (1976): Roughly ten weeks of exceptional heat, with temperatures surpassing 100°F at several locations across the country, accompanied by a prolonged drought — some areas went 45 days without rain.
The world is getting hotter, and faster. According to NOAA and NASA data, the five hottest years on record are 2024, 2023, 2016, 2020, and 2019 and 2017 (tied). The CBC reports that Environment and Climate Change Canada forecasts 2026 will likely rank among the four hottest years ever recorded.
Oxford research suggests warming will accelerate: nearly half the global population — some 3.79 billion people — could be living with extreme heat by 2050 if warming reaches 2.0°C above pre-industrial levels, a scenario climate scientists consider increasingly likely.
The Council on Foreign Relations has warned that the situation could worsen further. As the authors of a recent CFR paper explain, global warming can trigger environmental shifts that release additional greenhouse gases, creating a feedback loop of rising temperatures and accelerating emissions.
