2023 confirmed as the hottest year on record

The Copernicus Climate Change Service (C3S), implemented by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission, has reported that 2023 was the warmest calendar year ever based on global temperature data records going back to 1850, thanks to unprecedented global temperatures from June onwards.

The Global Climate Highlights 2023 report, based mainly on the ERA5 reanalysis dataset, presents a general summary of 2023’s most relevant climate extremes and the main drivers behind them. The report found that 2023 had a global average temperature of 14.98°C — 0.17°C higher than the previous highest annual value in 2016. 2023 was also 0.60°C warmer than the 1991–2020 average and 1.48°C warmer than the 1850–1900 pre-industrial level — putting it dangerously close to the 1.5°C limit set by the Paris Agreement.

The earliest signs of how unusual 2023 was to become began to emerge in early June, when temperature anomalies relative to 1850–1900 pre-industrial level reached 1.5°C for several days in a row. Although this was not the first time daily anomalies had reached this level, this had never previously happened at this time of the year. For the rest of 2023, global daily temperature anomalies above 1.5°C became a regular occurrence, to the point where close to 50% of days in 2023 were in excess of 1.5°C above the 1850–1900 level and two days in November were more than 2°C warmer.

Each month from June to December in 2023 was warmer than the corresponding month in any previous year, with July and August found to be 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 and 1.78°C above the 1850–1900 level for the month.

Surface air temperature anomaly for 2023 relative to the average for the 1991–2020 reference period. Data source: ERA5. Image credit: C3S/ECMWF. For a larger image, click here.

A large number of extreme climate events were recorded across the globe, including heatwaves, floods, droughts and wildfires. Estimated global wildfire carbon emissions in 2023 increased by 30% with respect to 2022, driven largely by persistent wildfires in Canada. And while Australia was the only continent that did not see large areas register record temperatures, there were still deadly floods, storms and fires across the country.

2023 was also remarkable for Antarctic sea ice, which reached record low extents for the corresponding time of the year in eight months. Both the daily and monthly extents reached all-time minima in February 2023, while Arctic sea ice extent at its annual peak in March ranked amongst the four lowest for the time of the year in the satellite record.

A critical driver of the unusual air temperatures experienced throughout 2023 was the unprecedented high sea surface temperatures (SSTs), which remained persistently and unusually high. Indeed, the global average SSTs for the period between April and December were the highest for the time of year in the ERA5 dataset. These high SSTs were associated with marine heatwaves around the globe, including in parts of the Mediterranean, the Gulf of Mexico and the Caribbean, the Indian Ocean and North Pacific, and much of the North Atlantic.

The main long-term factor for high ocean temperatures is the continuing increase in concentrations of greenhouse gases — which in 2023 reached their highest levels ever recorded in the atmosphere — but an additional contributing factor in 2023 was the El Niño Southern Oscillation (ENSO). However, the report found that the transition to El Niño alone does not explain all of the increase in ocean surface temperatures at a global scale in 2023, as high SSTs outside of the equatorial Pacific contributed significantly to the record-breaking global SSTs.

“2023 was an exceptional year, with climate records tumbling like dominoes,” said Samantha Burgess, Deputy Director of C3S. “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.”

“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 civilisation developed,” added Carlo Buontempo, Director of C3S. “This has profound consequences for the Paris Agreement and all human endeavours.

“If we want to successfully manage our climate risk portfolio, we need to urgently decarbonise our economy whilst using climate data and knowledge to prepare for the future.”

Top image credit: iStock.com/peepo