The global average temperature on Friday was more than two degrees Celsius hotter than pre-industrial levels for the first time on record, Europe's Copernicus climate monitor said Monday.
Months of extraordinary heat is expected to make 2023 the hottest year in history, with droughts, massive wildfires and fierce storms ravaging swathes of the planet.
According to provisional data, global temperatures on November 17 were 2.06C above the pre-industrial average, Samantha Burgess, Deputy Head of the EU's Climate Change Service (C3S) said on X, formerly known as Twitter.
"This was the first day when global temperature was more than 2C above 1850-1900 levels," she added.
The 2015 Paris Agreement enshrined the goal of holding the increase in the global average temperature to "well below" 2C above pre-industrial levels and to aim for a safer 1.5C.
One day above 2C does not mean that the Paris threshold has been breached - the deal instead refers to change measured over decades.
Climate experts have since urged the world to aim for the lower limit to avoid major climate impacts, such as heatwaves, super hurricanes and melting ice caps.
They defined warming as "the increase in the 30-year global average" relative to the average from 1850 to 1900.
The current climate is considered to have warmed by nearly 1.2C compared to that reference period.
The first day to exceed the 2C target is part of a series of records this year: October was the warmest ever recorded globally, as was every month since June, according to Copernicus, which said that 2023 would with "near certainty" surpass the hottest year on record set in 2016.
Beyond these official records, scientists say proxy data for the climate going back further - like tree rings or ice cores - suggests the temperatures seen this year could be unprecedented in human history, potentially the warmest in more than 100,000 years.
October was 1.7C warmer than an estimate of that month's average for the pre-industrial era, Copernicus said earlier this month.
And global average temperatures since January have been the highest in records going back to 1940, the monitor added, registering 1.43C above the 1850-1900 pre-industrial average.
Leaders meeting November 30 to December 12 in the United Arab Emirates for the COP28 conference will have to respond to a damning progress report on the world's Paris pledges after major scientific studies have made clear the world is far off track.
The conference is expected to draw up the first official assessment of the Paris Agreement and, if possible, corrective measures.