Global Climate Highlights 2023 (2024)

Global temperatures: 2023 warmest year on record, close to 1.5°C above pre-industrial level

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2023 has replaced 2016 as the warmest calendar year on record. According to the ERA5 dataset, the global-average temperature for 2023 was 14.98°C, 0.17°C higher than recorded for 2016.

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The year-to-year increase in global-average temperature was exceptionally large from 2022 to 2023.It follows a transition from three years of La Niña in 2020–2022 to El Niño conditions in 2023, although other factors appear to have also played a role. Further discussion is given in the section on sea surface temperature as well as in the highlight box: Was the unusual warmth of 2023 expected.

The evolution of the daily global-average temperature shows that 2023 is noteworthy for the occurrence of the highest global temperatures on record, both in absolute terms, during July, and relative to the annual cycle, during November. Almost all days from the beginning of June were the warmest in the ERA5 data record for that particular day of the year.

All days in 2023 were more than 1ºC above the pre-industrial level

The approach of the climate system towards the 1.5°C and 2°C limits of the Paris Agreement is usually discussed for temperatures that have been averaged globally and over each year of one or more decades. Observational datasets whose coverage includes the 1850-1900 reference period have monthly resolution, however, enabling estimates to be made of the annual variation in the warming from 1850-1900 to the recent past. This provides a basis for monitoring the accumulation of daily exceedances of the warming limits using reanalysis datasets such as ERA5.

Using ERA5, this monitoring shows that all days of 2023 had global temperatures more than 1°C warmer than the 1850-1900 level for that time of year. Two days were more than 2°C warmer than 1850-1900, the first time the 2°C level has been exceeded. Close to 50% of days in 2023 were in excess of 1.5°C warmer than 1850-1900. This was the case for just over 20% of days in 2016, the previous warmest year on record. The earliest period in ERA5 with daily temperatures successively at least 1.5°C warmer than 1850-1900 is 2-15 December 2015.

Regional variations

The distribution of surface air temperature anomalies across the globe in 2023 shows a marked contrast with that of 2022. Almost all land areas experienced above-average temperatures in 2023. Annual temperatures were more than 1°C higher than the 1991-2020 average over much of Europe and North America, and over several other regions.

Marine air temperatures were also the warmest on record for several regions in 2023. This is the case for much of the North Atlantic and Caribbean, northern, tropical and southern parts of the Pacific, and parts of the South Atlantic and Indian Oceans. The air temperature anomalies for these and other regions are tied closely to anomalies in sea surface temperatures (SSTs). The only sizeable region where marine air temperatures were the coldest on record was southwest of South America. The contrast in temperatures over the tropical and southern subtropical eastern Pacific Ocean between 2022 and 2023, from coldest to close-to-warmest on record, illustrates the transition from La Niña to El Niño conditions discussed further below.

How did different regions contribute to the global temperature anomaly?

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The rise in air temperature since the mid-1970s has been about twice as large over land as over ice-free ocean, but each surface accounts for about half of the rise in global-average air temperature, as the area of the Earth’s surface covered by ocean is much larger than the area covered by land. The monthly evolution of the contribution of various regions to the global temperature anomaly in 2022 and 2023 is illustrated above. The increase in temperature anomaly from May to August 2023 was associated with a relatively large contribution from warm temperatures over the ocean. Temperatures anomalies over the tropical ocean shifted from negative in 2022 to positive in 2023, associated both with the transition from La Niña to El Niño over the Pacific Ocean and with generally warmer temperatures over the Atlantic and Indian Oceans. The particularly large anomalies in the final four months of 2023 are associated with significant contributions from both ocean and land, primarily from the tropics (especially over ocean) and the northern extratropics (especially over land).

Sea surface temperatures: transition to El Niño and record global values

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2023 has seen record-breaking SSTs around the globe, including the highest daily global SST in the ERA5 record, and every month from April through to December saw global SSTs reach record levels for the time of year. Typically, SSTs reach their highest level for the year in March and then begin to fall, before a slight increase again during July and August. In 2023, 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 in ERA5 of 21.02°C on 23 and 24 August, which is higher than the previous record of 20.95°C, set in March 2016 towards the end of a strong El Niño event. Throughout the rest of the year, global-average SSTs remained unusually high and well above the previous warmest years.

Last year also marked a shift in the El Niño Southern Oscillation (ENSO). The start of 2023 saw the end of a rare ‘triple-dip’ La Niña, where the cool phase of ENSO persisted for three years from 2020 until Spring 2023. Later in Spring, the first signs of a transition to El Niño appeared, with WMO declaring the onset of El Niño in early July. While this El Niño event continued to strengthen and contributed to the warmth of 2023, it has not been as strong as those events experienced in 2015 and 1997.

High SSTs outside of the equatorial Pacific also played an important role in the record-breaking global SSTs. This is particularly true in the North Atlantic, which has seen exceptional SSTs throughout June to December, with monthly anomalies well above average for the time of year and daily SST records broken. The previous highest daily SST for the North Atlantic was 24.81°C, set in September 2022, and on 31 August 2023 the SST reached 25.19°C. The boreal summer months saw marine heatwaves across large sectors of the North Atlantic. The warm tropical Atlantic SSTs also contributed to an above-normal hurricane season, ranking 4th for the most named storms in a year since 1950, and seeing the most named storms of any El Niño influenced year. Marine heatwaves were also observed in parts of the North Pacific and Indian Oceans, around New Zealand, in the Gulf of Mexico and the Caribbean and in the Mediterranean. These can have significant and sometimes devastating impacts on ocean ecosystems and biodiversity, and lead to socio-economic impacts.

Was the unusual warmth of 2023 expected?

Yes and no. Yes, in the sense that a year as warm as 2023 was seen as being inevitable in due course due to a combination of continued climate warming and an occurrence of El Niño. This trend could be inferred by extrapolating observation-based time series or by examining the range of possibilities indicated by climate projections used in the Sixth Assessment Report of the IPCC. More specifically, the WMO reported in 2022 that decadal forecasts estimated there was a 48% chance that the global temperature would exceed 1.5°C above the pre-industrial level in at least one year between 2022 and 2026. That chance was increased to 66% for the period 2023-2027 in an updated report published in 2023.

No, in the sense that there were additional unforeseen factors - some of which are still under scientific investigation -that contributed to the extremity of global temperatures in 2023. Forecasts from ten climate prediction centres were indicating late in 2022 that there was only a very low probability that the annual temperature for 2023 would be as high as it was.

The temperatures observed in the later months of 2023 were not only record high relative to the average for 1991-2020, but also relative to a climatological average adjusted to the present day, considering the average rate of temperature increase of about 0.2°C/decade recorded since 1979. The change in annual temperature from 2022 to 2023 was larger than any change from one year to the next in the ERA5 data record. 2023 is also unusual in that its record temperature is for a year in which the El Niño was building up rather than declining.The latter was the case in 2016 and 1998, for example. Moreover, the El Niño in 2023 was weaker than in the build-up phases of the strong 1997/98 and 2015/16 events.

This all shows that the record temperatures in 2023 are not only due to El Niño and general global warming. A comprehensive attribution for the year as a whole is not yet available, but the warmth of SSTs across the globe, the record low extent of Antarctic sea-ice and extremes over land are evident factors, even if the relative contributions of natural variability and climate change are less obvious. Several changes in forcing factors have also been identified as likely minor contributors: enhanced stratospheric water vapour due to the eruption in January 2022 of the Hunga Tonga–Hunga Haʻapai volcano, reduced aerosols due to lower sulfur dioxide emissions by shipping, and the approach of the current solar cycle to its peak.

What are the expectations for 2024? A recently released forecast for the year suggests that it could be warmer still than 2023, with a reasonable probability that the calendar year will end with an average temperature in excess of 1.5°C above the pre-industrial level according to multiple datasets. More immediate is the possibility that the twelve consecutive months ending in January and/or February 2024 will exceed the 1.5°C level according to ERA5, as January and February 2023 were not especially warm months.

Extreme events around the world

Extreme events around the world in 2023 had significant impacts on human health, ecosystems, nature and infrastructure. Among the most exceptional were flooding, wildfires, drought and extreme heat.

Impactful flooding events ranged from flash floods caused by intense rainfall, to large-scale flooding due to the passage of atmospheric rivers (such as in California in January and March, and over Chile in July), monsoon rainfall, large low-pressure systems and tropical cyclones. Cyclone Freddy impacted southeast Africa (February, March), Cyclone Mocha south and southeast Asia (May), Hurricane Hilary Mexico and the western USA (August), Hurricane Otis Mexico, (October), Storm Daniel the Mediterranean (September), and post-tropical cyclone Jasper Australia, (December), among others. In some cases, such as in the Horn of Africa during Autumn, flooding may have been exacerbated by particularly low soil moisture levels that favoured and accelerated runoff.

Many other regions across the globe suffered from prolonged lack of precipitation, in particular in North (Mexico) and South America (Amazon basin, Pantanal wetlands, Argentina, Uruguay) and western Africa. Heatwaves occurred around the world during 2023, often breaking national or local temperature records. Significant occurrences in southern Europe, North Africa, and parts of North America and Asia, were followed in seasonal progression by occurrences over parts of South America, southern Africa and Australia.

Hot and dry conditions in some regions also contributed to extensive wildfires, notably in southern Europe, Canada (in particular the Northwest Territories, and with significant contribution to global carbon emissions), South America, Australia and Hawaii, among others.

Sea ice: record low extents around Antarctic

Europe: high variability and many extreme events

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Temperatures were highly variable across Europe, especially in spring and summer when a stark contrast in conditions was observed across the continent. In both seasons, Europe as a whole saw above-average temperatures, but not record breaking; spring 2023, although clearly warmer than the two previous years, was not among the ten warmest in the data record. It saw Iberia and northeastern Europe experiencing well above-average temperatures and drier conditions for the season, whereas in a northwest-to-southeast band across Europe, temperatures were near-average and wetter-than-average conditions prevailed. May was the only month in the year with average conditions slightly below the climatological mean.

Summer was ranked fifth-warmest, with an average temperature of 19.63°C, 0.83°C above the 1991-2020 climatology, a year after the warmest European summer of 2022. June was hot and dry in northern Europe and colder than average in the south, whereas July and August were colder and wetter than average in northern Europe, while southern (July) and southwestern (August) Europe experienced heatwaves which resulted in multiple daily temperature records broken. This included marine heatwaves which affected both the Atlantic and the Mediterranean. Significant wildfires also occurred.

Particularly cold conditions occurred from October to December across Scandinavia, whereas the rest of the continent experienced above-average temperatures, making it the second-warmest autumn on record. The European-average temperature was 10.96°C, at 1.43°C above average, just 0.03°C cooler than autumn 2020.

Europe also experienced considerable storms and flooding. Significant flood events triggered by heavy, or record-breaking precipitation, occurred in Emilia-Romagna, Italy, in May; in Norway and Sweden (storm Hans) and Slovenia in August. In autumn, there were multiple storms and associated flooding including: in Greece in September (Storm Daniel, also behind devastating flooding in Libya); in October in northern and western Europe (Storm Babet); across the Iberian Peninsula (storm Aline); and across most of western Europe (Storm Ciarán). Further storms affected central (Storm Ciro) and northwestern Europe (Storms Elin, Fergus, Pia, Gerrit and Geraldine) in December.

The widespread heavy precipitation of 2023 only partly alleviated the persistent drier-than-average conditions over southern Iberia and France, part of the Alps, the eastern Balkans and a large region of eastern Europe.

Greenhouse gas concentrations: continued increase

The atmospheric concentration of the greenhouse gases carbon dioxide and methane continued to increase in 2023. Preliminary analysis of satellite data averaged over the whole atmospheric column, shows that carbon dioxide concentrations are approximately 2.4 ppm (+/- 0.4 ppm) higher in 2023 compared to 2022, while methane rose by around 11 ppb (+/- 3 ppb). This resulted in an annual average for 2023 of approximately 419.3 ppm for carbon dioxide and 1902 ppb for methane. The increase of CO₂ is similar to the increase observed in recent years.

The increase of methane remains high but is not as high as for the last three years. Atmospheric concentrations of methane had substantially grown throughout the 20th century, to stall from 2000 to 2006. Based on additional data sources, including in situ and measurements from ice cores, the atmospheric CO₂ concentrations were higher in 2023 than at any time in at least 2,000,000 years. Atmospheric concentrations of CH₄ in 2023 were higher than at any time in at least 800,000 years.

Further Reading

Footnotes

[1]When we use the term ‘temperature’ here, we mean the temperature close to the Earth’s surface, hence the term ‘surface air temperatures.’ For land surfaces, this usually refers to the air temperature at a 2m height above the surface. For the ocean, this can either refer to the same 2m air temperature, or to the temperature of the ocean or sea surface layer. This is dependent on the dataset used.

[2] This has been estimated using JRA-3Q analysis data over land and JRA-3Q background forecast data over sea, to avoid possible problems arising from biases in temperature observations from ships. This is equivalent to what is done in ERA5, which analyses surface air temperature observations only over land.

[3] The findings about global sea surface temperatures (SSTs) presented here are based on SST data from ERA5 averaged over the 60°S–60°N domain. Note that ERA5 SSTs are estimates of the ocean temperature at about 10m depth (known as foundation temperature). The results, e.g. date of the highest value in 2023, may differ from other SST products providing temperature estimates at different depths, such as 20cm depth for NOAA’s OISST.

Access to data

Time series and maps data can be accessed directly through the links provided.
Data from Copernicus are subject to the License to Use Copernicus Products (v 1.2). Datasets from other providers, which are included here, mainly for the purpose of comparison, are subject to other licences; please check with the respective provider.

C3S ERA5 1950–2022: Data | Documentation
EUMETSAT OSI SAF Sea Ice Index v2.2 Data and Documentation
C3S climate data record XCO₂ (2003-2022) Data | Documentation
C3S climate data record XCH₄ (2003-2022) Data | Documentation
GFAS V1.2 wildfire emissions Data | Documentation
CAMS near real-time data record XCO₂ V3.1 Data and Documentation
CAMS near real-time data record XCH4 available at FTP: [email protected], directory: /pub/pub/RemoTeC/PROXY_NRT_L1X/.