The global temperature averaged 14.98 degrees Celsius last year, up by 0.17 degree Celsius from 2016, which was the previous warmest year on record, according to findings outlined in the 2023 Global Climate Highlights report.
From June onward, each month in 2023 experienced higher temperatures than any corresponding period in recorded history, with July and August standing out as the warmest months on record.
For the first time, each day through the past year was at least one degree Celsius above the 1850-1900 pre-industrial level for that time of year, the report said.
C3S Deputy Director Samantha Burgess described 2023 as an exceptional year "with climate records tumbling like dominoes."
"Temperatures during 2023 likely exceed those of any period in at least the last 100,000 years," she added.
A critical driver of the unusual air temperatures throughout 2023 was the unprecedentedly high sea surface temperatures (SSTs).
"Global-average SSTs rose sharply in March, with a slight dip in April and May, but continued to rise throughout the boreal summer months to reach the highest value of 21.02 degrees Celsius on Aug. 23 and 24," the report said.
The primary long-term factor contributing to elevated ocean temperatures is the continuing increase in concentrations of greenhouse gases but an additional contributing factor in 2023 was the El Nino Southern Oscillation, the report said.
Atmospheric concentrations of carbon dioxide and methane continued to rise, reaching record levels in 2023 at 419 ppm and 1902 ppb, respectively, it said.
The rise in temperatures has resulted in extreme events worldwide, including heatwaves, floods, droughts and wildfires. Notably, it has also impacted sea ice in both the Arctic and the Antarctic, according to the report.