July 3 was Earth’s hottest day on record — until July 4.

The world broke an all-time heat record this week — twice. For two days in a row, the planet’s daily temperature soared to the highest ever measured by humans, according to data from the National Centers for Environmental Prediction. Earth’s thermostat touched a record 62.62 degrees Fahrenheit on Monday, then inched up to 62.92 degrees Fahrenheit (17.18 degrees Celsius) on Tuesday. Extreme heat, made more likely by climate change and the planet-warming El Niño weather pattern that just took hold, has gripped much of the United States and world in...