The European Union's Copernicus Climate Change Service (C3S) released its 2023 Global Climate Highlights report on Tuesday, backing up scientific consensus that 2023 was the hottest year on record. 

The report shows 2023 had a global average temperature of 14.98 Celsius (58 Fahrenheit). This constitutes a 0.17 C global increase, meaning 2023 overtakes 2016, the previous record-breaking year, by "a large margin."

The high average temperatures were tied to several drivers such as greenhouse gas concentrations and El Nino, a warm phase in the Pacific Ocean, according to authors.

Samantha Burgess, Deputy Director of C3S, said in a statement that "2023 was an exceptional year with climate records tumbling like dominoes. Not only is 2023 the warmest year on record, it is also the first year with all days over 1 C warmer than the pre-industrial period."

"Temperatures during 2023 likely exceed those of any period in at least the last 100,000 years," she added.

Consequences for global climate policy 

Carlo Buontempo, director of C3S, said that the findings have "profound consequences" for the Paris Agreement.

"The extremes we have observed over the last few months provide a dramatic testimony of how far we now are from the climate in which our civilization developed," Buontempo said.

Leaders from 196 countries that have signed the Paris Agreement, a legally binding international treaty on climate change, agreed to hold "the increase in the global average temperature to well below 2 C above pre-industrial levels" and pursue efforts "to limit the temperature increase to 1.5 C above pre-industrial levels."

The UN's Intergovernmental Panel on Climate Change (IPCC) has issued repeated warnings that an average temperature increase topping the 1.5 C threshold risks "unleashing far more severe climate change impacts, including more frequent and severe droughts, heatwaves and rainfall."

2023 saw unprecedented heatwaves in southern Europe, extreme drought in the Horn of Africa, record winter highs in South America and weather exacerbating wildfires in Canada. 

"Such events will continue to get worse until we transfer away from fossil fuels and reach net-zero emissions," said Ed Hawkins, climate change professor at the University of Reading, who did not contribute to the report. "We will continue to suffer the consequences of our inactions today for generations." 

Almost half of 2023 exceeded the 1.5 C limit, and some scientists predict that the Earth's average surface temperature is also likely to breach 1.5 C in 2024.

However, that would not necessarily mean that the world failed to meet the Paris Agreement target, as that would occur only after several successive years above the 1.5 C.

Warmest December on record 

At one point in 2023, the daily global temperature average briefly surpassed the pre-industrial levels by more than 2 C.

In June 2023, temperature anomalies spiked above the pre-industrial level 1.5 C for several days in a row. Eventually, nearly half the days in 2023 were more than 1.5 C higher than pre-industrial levels, as per the report.

July and August 2023 were the warmest two months on record.

December 2023 was the warmest December on record globally, with an average temperature of 13.51 C — 0.85 C above the 1991-2020 average.

Sea surface warming 

Earth's sea surface temperatures were "persistently and unusually high", the report said, reaching record levels from April to December 2023.

This was because of marine heatwaves around the globe including in parts of the Mediterranean, the Gulf of Mexico, the Caribbean, Indian Ocean, North Pacific and much of North Atlantic.

Researchers have found increased air temperatures, which transfer heat into the ocean, are making marine heatwaves more frequent 

Moreover, in the spring of 2023, the cooler oceanic phase La Nina came to an end and El Nino conditions began to develop. 

For Europe, 2023 was the second-warmest year — 0.17 C cooler than 2020.