'We are in uncharted territory': World records hottest day ever for the third time in just four days

The planet registered its hottest day since records began for the third time in just four days this week, deepening fears about the far-reaching changes taking place in Earth's system because of the climate emergency.

Unofficial data from U.S. researchers showed the planet's daily average temperature soared to 17.23 degrees Celsius (63.01 degrees Fahrenheit) on Thursday, surpassing two previous heat records registered in recent days.

The extraordinary feat comes shortly after the European Union's climate change service confirmed the planet observed its hottest June on record, with unprecedented sea surface temperatures and record low Antarctic sea ice.

Climate scientists are deeply concerned.

Indeed, the U.N. weather agency recently warned that the combination of ever-increasing greenhouse gas emissions and the return of El Niño is likely to mean the worst is still to come.

"The global temperature record smashed again yesterday," Bill McGuire, professor emeritus of geophysical and climate hazards at University College London, said via Twitter.

"I would say welcome to the future — except the future will be much hotter."

The University of Maine's Climate Reanalyzer, an unofficial tool that measures global air temperatures at 2 meters above the surface, has registered the temperature records. The data, which stretches back to 1979, is often used by climate scientists as a reference to the world's condition.

On Monday, the global average temperature was found to have climbed to 17.01 degrees Celsius, surpassing 17 degrees Celsius for the first time in 44 years — when the data was first collected.

The record was broken again on Tuesday, notching 17.18 degrees Celsius and remained at this record high level on Wednesday.

The previous record high came in 2016, the hottest year ever recorded, when in August of that year the metric showed the global average temperature reached 16.92 degrees Celsius.

"Global air temperatures just keep going up!" climate researcher Leon Simons said via Twitter, citing the multiple heat records observed this week.

It follows a series of mind-bending extreme weather events in recent months, with climate-fueled heat waves recorded in China, northern Africa, the western Mediterranean, Mexico and the southern U.S.

"We are in uncharted territory and we can expect more records to fall as El Niño develops further and these impacts will extend into 2024," Chris Hewitt, director of climate services at the World Meteorological Organization, said in a report published Thursday.

"This is worrying news for the planet."