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 Centres 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.
