July 21 was the hottest day ever registered globally, according to preliminary data published on Tuesday by the EU's climate monitor.

The Copernicus Climate Change Service (C3S) said the global average surface air temperature of 17.09 degrees Celsius (62.7 degrees Fahrenheit) on Sunday was the warmest in their record books, which go back to 1940.

"The Earth has just experienced its warmest day," the monitor said in a statement.

The new daily high was just 0.01C above the previous record temperature of 17.08C registered on July 6, 2023.

"On July 21st, C3S recorded a new record for the daily global mean temperature," said C3S director Carlo Buontempo in a statement.

"We are now in truly uncharted territory and as the climate keeps warming, we are bound to see new records being broken in future months and years," he added.

Copernicus said the daily record could be breached again in coming days before temperatures are expected to drop off, though there could be fluctuations in the weeks ahead.

Every month since June 2023 has eclipsed its own temperature record, and the latest daily high comes as heatwaves bake parts of the United States and Europe. 

Record temperatures in Southern and Eastern Europe 

Southern Europe was among the regions with the hottest weather in the past few days. 

An unrelenting heatwave blanketed swathes of southern and eastern Europe, with dozens of cities on red alert as scorching temperatures fuel wildfires, strain power grids, and make daily life unbearable.

The mercury hovered near or above 40 degrees Celsius in many countries.

Greece, which recorded its earliest-ever heatwave this summer, withered through two weeks of temperatures at around 40C.

Nights in the capital Athens hit 30C.

On Thursday, authorities closed the Acropolis, the country's most visited attraction, during the hottest hours for a second day in a row.

Some outdoor work, like construction and meal delivery, were also suspended.

 In Italy, zoo keepers gave animals ice blocks to ward off heat stroke as temperatures soared, while 14 cities including Florence, Palermo and Bologna were placed on red alert.

To make matters worse, swarms of locusts thriving in the hot conditions invaded fields and orchards in the eastern region of Emilia Romagna. 

"The high temperatures and the lack of rain have favoured the massive proliferation of one of the insects most feared by farmers," said Italy's main agricultural lobby Coldiretti.

In Hungary, which has been under a maximum heat warning since July 7, searing temperatures warped an airport runway while the state-run train operator urged passengers to take air-conditioned buses instead of its outdated rail cars.

Croatia and Serbia consumed a record amount of electricity as residents switched on air conditioners to beat the heat.

It followed an early start to the Balkans summer in June when a sudden heatwave saw power grids overwhelmed in Albania, Bosnia, southern Croatia and Montenegro.

Ilan Kelman from University College London said prolonged heatwaves could turn deadly if the human body was not given ample chance to cool off at night.

"This is what we need to be worried about. Temperatures are not falling at night," said the professor of disasters and health.

The past 13 months have been the hottest ever recorded, and heatwaves have already this year hit North America, Mexico, India and Thailand, to name a few.

The EU's climate monitor Copernicus said the average temperature for June across Europe was 1.57C above the 1991–2020 average, making the month the joint-second warmest on record.