'Terrifying': Tuesday topples Monday as hottest day ever recorded on Earth

"Not a milestone we should be celebrating," said one climate scientist. "It's a death sentence for people and ecosystems."

Data from the U.S. National Centers for Environmental Prediction shows that the average global temperature reached 17.01°C, or 62.62°F, on Monday—making it the hottest day ever recorded.

The record lasted just 24 hours.

On Tuesday, the global average temperature peaked at a new all-time high of 17.18°C as regions worldwide—from Asia to Africa to the U.S. South—reeled from dangerous heatwaves.

As Bloomberg reported, "The heat this summer has already put millions of people around the world at risk."

"China is experiencing a scorching new heat wave less than two weeks after temperatures broke records in Beijing," the outlet noted. "Extreme heat in India last month has been linked to deaths in some of its poorest regions. Last week saw a dangerous heat dome cover Texas and northern Mexico, while the U.K. baked in its hottest June on record."

Earth's hottest day came after the World Meteorological Organization (WMO) declared the onset of El Niño conditions, which are marked by warming surface waters in the Pacific.

"The onset of El Niño will greatly increase the likelihood of breaking temperature records and triggering more extreme heat in many parts of the world and in the ocean," WMO Secretary-General Petteri Taalas said in a statement Tuesday. "The declaration of an El Niño by WMO is the signal to governments around the world to mobilize preparations to limit the impacts on our health, our ecosystems, and our economies."

"Early warnings and anticipatory action of extreme weather events associated with this major climate phenomenon are vital to save lives and livelihoods," he added.

Record temperatures and intensifying extreme weather, including an unprecedented wildfire season in Canada, come as world leaders are facing urgent calls to rein in fossil fuels—the primary driver of the global climate emergency—at the upcoming COP28 climate conference in the United Arab Emirates, one of the world's top oil producers.

"People around the world are already enduring climate impacts, from heatwaves, wildfires, and air pollution to floods and extreme storms," Jeni Miller, executive director of the California-based Global Climate and Health Alliance, toldThe Guardian on Tuesday. "Global warming is also exacerbating crop losses and the spread of infectious diseases, as well as migration."

"Governments must prepare to deliver a commitment at COP28 to phase out all fossil fuels, and a just transition to renewable energy for all," Miller said.

Friederike Otto, a climate scientist at the Grantham Institute for Climate Change and the Environment at Britain's Imperial College London, toldReuters that the hottest global temperature ever recorded is "not a milestone we should be celebrating."

"It's a death sentence for people and ecosystems," Otto added.