The world's average temperature reached a new high on Monday 3 July, topping 17 degrees Celsius for the first time.
US researchers said the new record was the highest in any instrumental record dating back to the end of the 19th century.
Scientists believe a combination of a natural weather event known as El Niño and mankind's ongoing emissions of carbon dioxide are driving the heat.
Last month has also been confirmed as the world's warmest June yet recorded.
Scientists at the US National Centers for Environmental Prediction said that the world's average temperature had reached 17.01C on 3 July, breaking the previous record of 16.92C that had stood since August 2016.
Since the start of this year, researchers have been concerned about rising temperatures on land and at sea.
Record spring heat in Spain and many countries in Asia have been followed by marine heatwaves in places that don't normally see them, such as the North Sea.
This week China continued to experience an enduring heatwave with temperatures in some places above 35C, while the southern US has also been subject to stifling conditions.
Monday's high is the warmest since satellite monitoring records began in 1979. Experts also believe it is the highest since widespread instrumental records began towards the end of the 19th century.
Researchers believe that the new global high is a combination of the naturally occurring El Niño event and ongoing emissions of carbon dioxide.
The El Niño Southern Oscillation, or ENSO, as it is properly called, has three different phases: Hot, cold or neutral. It is the most powerful fluctuation in the climate system anywhere on Earth.
"The average global surface air temperature reaching 17C for the first time since we have reliable records available is a significant symbolic milestone in our warming world," said climate researcher Leon Simons.
"Now that the warmer phase of El Niño is starting we can expect a lot more daily, monthly and annual records breaking in the next 1.5 years."
Monday's record temperature comes as the month of June was confirmed as the hottest June in the global record. Average temperatures across the planet were 1.46C above the average in the period between 1850 and 1900.
The UK also recorded its hottest June while the impact of high temperatures is also being felt at the world's extremes. In Antarctica, the July temperature record was broken with a reading of 8.7C taken at Ukraine's Vernadsky Research base.
Scientists believe that more records will be shattered as the summer goes on and El Niño gains strength.
"Chances are that July will be the warmest ever, and with it the hottest month ever: 'ever' meaning since the Eemian which is some 120,000 years ago," said Karsten Haustein, from the University of Leipzig.
"While Southern Hemisphere temperatures will drop a bit in the next few days, chances are that July and August will see even warmer days yet given that El Niño is now pretty much in full swing".
BBC
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