OBSERVER: 2023 - A year of unprecedented heat and climate extremes

Earlier this year, the Copernicus Climate Change Service (C3S) Global Climate Highlights 2023 Summary confirmed 2023 as the warmest year on record, with global temperatures reaching an alarming 1.48 degrees Celsius above preindustrial levels. This unprecedented rise in temperature, underscored by a series of extreme weather events, from devastating droughts and wildfires to marine heatwaves, signals an urgent call for action. Analysing the ERA5 dataset, the report highlights the significant impact of shifts from La Niña to El Niño conditions and the continuous increase in greenhouse gas concentrations, driving home the critical need for global decarbonisation efforts and the strategic use of climate data to navigate the challenges of a warming world and safeguard our future. 

Record-breaking temperatures 

2023 has witnessed an unparalleled surge in global temperatures, setting a new record with an average annual value of 14.98°C, surpassing the previous high in 2016 by 0.17°C. This increase has been consistent, with temperatures from June to December each month being warmer than any corresponding month in past records. The boreal summer, spanning June to August, was notably the warmest season ever recorded. 

The daily temperature records offer a vivid depiction of the ongoing warming trend, marking the first time in recorded history in which every day of a year exceeded pre-industrial levels by 1°C. The frequency of days crossing the 1.5°C threshold approached 50%, with two days in November above the 2°C mark, illustrating the continued impacts of climate change. 

Analysis by C3S using the ERA5 dataset, which including climate records dating back to 1940, confirms these findings, aligning with several other global temperature datasets and indicating that 2023 was the warmest year since 1850, the year records started being collected. The ERA5 dataset shows that 2023 was not only 0.17°C warmer than 2016 but also 0.60°C above the 1991-2020 average, and a staggering 1.48°C warmer than the pre-industrial levels of 1850-1900. The report also highlights the likelihood of a 12-month period ending in January or February 2024 exceeding the 1.5°C threshold above pre-industrial levels. 

The exceptional warmth of 2023 was evident across the entire year, with each month from June to December setting new records for warmth. July and August were the warmest months on record, contributing to the boreal summer being the warmest season ever documented. September 2023 stood out with a temperature deviation of 0.93°C above the 1991-2020 average, the largest deviation for any month in the ERA5 dataset. October, November, and December each recorded a temperature 0.85°C above the average, ranking them among the highest deviations observed. 

In revealing this significant warming trend that exceeded the records set in 2016 and the pre-industrial average by a never-seen-before margin, the Global Climate Highlights Summary underscores the extraordinary nature of the climate phenomena observed throughout the year and marks a critical point in the current and future challenges stemming from climate change. 

Factors influencing the unusual warmth

The transition from La Niña to El Niño conditions significantly influenced the global temperature rise in 2023. This shift contributed to the record-breaking sea surface temperatures (SSTs) observed from April through December. The North Atlantic, in particular, recorded exceptionally high temperatures, which played a pivotal role in the global warmth experienced. Additionally, the reduced extent of Antarctic sea ice further exemplified the unusual climatic conditions of the year. These factors, combined with the general trend of global warming, underscore the complex interplay of natural variability and human-induced climate change driving the planet towards unprecedented warmth.

The year-to-year increase in global-average temperature was considerable from 2022 to 2023 and can be partly attributed to a shift from La Niña conditions in 2020–2022 to El Niño conditions in 2023. However, warm ocean temperatures outside the tropical Pacific were also a factor, especially in the North Atlantic, contributing to record-high global sea surface temperatures. These warmer waters were associated with marine heatwaves in various places like the Mediterranean, Gulf of Mexico, Caribbean, Indian Ocean, North Pacific, and much of the North Atlantic. The reduction in marine sulphur aerosols from shipping due to the phasing out of high-sulphur marine fuels in 2020, is also expected to have had a marginal impact on the global average temperature increase, underscoring the myriad of factors influencing the year's exceptional warmth.

Greenhouse gas concentrations continue to rise

Meanwhile, the concentration of greenhouse gases continued its upward trajectory, exceeding those observed in recent history. In 2023, carbon dioxide concentrations reached 419 ppm, and methane concentrations reached 1902 ppb. Preliminary analyses of satellite data revealed an increase from 2022 of approximately 2.4 ppm for carbon dioxide and 11 ppb for methane. The report goes on to make the shocking revelation that further analysis based on measurements from ice cores and other additional data sources indicate that the atmospheric CO2 concentrations were higher in 2023 than any other time in the last 2 million years. The observed increasing concentration of these greenhouse gases underscores their significant role in driving global warming and highlights the urgency of mitigating emissions.

The climate outlook for 2024

Current data and forecasts suggest that 2024 is shaping up to be another record-breaking year in terms of global temperatures. Forecasts from the UK Met Office and Barcelona Supercomputing Centre indicate that 2024 could be even warmer and that more unprecedented temperatures such as those observed in 2023 could be recorded, with a reasonable probability that global average temperatures will exceed the 1.5°C threshold above pre-industrial levels. This expectation is largely due to the historical pattern observed with El Niño events, during which their effect on global mean temperatures tends to be larger in the year following their peak.  

The most recent seasonal forecast from Copernicus Climate Change Service published on February 10, 2024 indicates that the El Niño event has likely peaked and will continue to decay over a six-month forecast period. By the middle of the year 2024, La Niña conditions are predicted more likely than a continuation of El Niño. Further ahead, the recent long-range forecast from the European Centre for Medium-Range Weather Forecasts (ECMWF) suggests that La Niña or neutral conditions are the likely pattern. 

The shift towards La Niña conditions implies a potential cooling effect on the global average temperature, contrasting with the warming trend observed during El Niño. However, it is important to note that this natural variability is superimposed on the long-term warming trend caused by human-induced increases in greenhouse gases. In fact, recent La Niña years have been warmer than El Niño years from earlier decades, underscoring the dominant influence of anthropogenic global warming. The La Niña year of 2020, for example, tied with 2016—a year which started with a significant El Niño—as the all-time-record-high global surface temperature. Therefore, while the forecasted transition to La Niña may moderate the rate of temperature increase in the short term, it will not counteract the overarching trend of global warming while the ongoing rise in atmospheric concentrations of greenhouse gases are expected to continue driving the global average temperature upwards.

Reflecting on the report’s findings, Carlo Buontempo, Director of Copernicus’ Climate Change Service, said: “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. 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.”