Introduction
Authors: Boyer T. , Blunden J. , Dunn R. J. H. , Ades Melanie , Adler Robert , Adusumilli Susheel , Agyakwah W. , Ahmadpour Somayeh , Aldeco Laura S. , Alexander Michael A. , Alexe Mihai , Alfaro Eric J. , Allan Richard P. , Allgood Adam , Alves Lincoln M. , Amador Jorge A. , Amaya Dillon J. , Amory Charles , Anderson John , Andrade B. , Andreassen Liss Marie , Anneville Orlane , Aono Yasuyuki , Arguez Anthony , Armenteras Pascual Dolores , Arosio Carlo , Asher Elizabeth , Augustine John A. , Avalos Grinia , Azorin-Molina Cesar , Baez-Villanueva Oscar M. , Baiman Rebecca , Ballinger Thomas J. , Banwell Alison F. , Bardin M. Yu. , Barichivich J. , Barreira Sandra , Beadling Rebecca L. , Beauchemin Marc , Beck Hylke E. , Becker Emily J. , Beckley Brian , Bekele E. , Bellouin Nicolas , Benedetti Angela , Berne Christine , Berner Logan T. , Bernhard Germar H. , Bhatt Uma S. , Bigalke Siiri , Bissolli Peter , Bjerke Jarle W. , Blake Eric S. , Blannin Josh , Blenkinsop Stephen , Bochníček Oliver , Bock Olivier , Bodin Xavier , Bonte Olivier , Bosilovich Michael G. , Boucher Olivier , Box Jason E. , Bozkurt Deniz , Brettschneider Brian , Bringas Francis G. , Brubaker Mike , Buehler Stefan A. , Bukunt Brandon , Burgess David , Butler Amy H. , Byrne Michael P. , Calderón Blanca , Camargo Suzana J. , Campbell Jayaka , Campos Diego , Cappucci Fabrizio , Carrea Laura , Carter Brendan R. , Cerveny Randall , Cetinić Ivona , Chambers Don P. , Chan Duo , Chandler Elise , Chang Kai-Lan , Charlton Candice S. , Chen Jack , Chen Lin , Cheng Lijing , Cheng Vincent Y. S. , Chisholm Lucy , Christiansen Hanne H. , Christy John R. , Chung Eui-Seok , Ciasto Laura M. , Clarke Leonardo , Clem Kyle R. , Clingan Scott , Coelho Caio A.S. , Coldewey-Egbers Melanie , Colwell Steve , Cooper Owen R. , Cornes Richard C. , Correa Kris , Costa Felipe , Covey Curt , Coy Lawrence , Crétaux Jean-Francois , Crimmins Theresa , Crotwell Molly , Culpepper Joshua , Cunha Ana P. , Cusicanqui Diego , Datta Rajashree T. , Davis Sean , de Jeu Richard A. M. , De Laat Jos , Deb Pranab , Decharme Bertrand , Degenstein Doug , Delaloye Reynald , Derksen Chris , Diamond Howard J. , DiGangi Elizabeth , Dindyal S. , Divine Dmitry , Dokulil Martin T. , Donat Markus G. , Dong Shenfu , Dorigo Wouter A. , Drost Jensen Caroline , Druckenmiller Matthew L. , du Plessis Marcel , Duchemin Diane , Dugan Hilary , Dulamsuren Dashkhuu , Durre Imke , Dutton Geoff , Duveiller Gregory , Earl-Spurr Craig , Echeverría Garcés Paola , Ekici Mithat , Elias Chereque Alesksandra , Elipot Shane , ElKharrim M. , Epstein Howard E. , Espinoza Jhan-Carlo , Estilow Thomas W. , Estrella Nicole , Farrell Sinead , Fauchereau Nicolas , Fausto Robert S. , Feely Richard A. , Fenimore Chris , Fereday David , Fernandez Denise , Fettweis Xavier , Fioletov Vitali E. , Flemming Johannes , Florentine Caitlyn , Fogarty Chris , Fogt Ryan L. , Forbes Bruce C. , Foster Michael J. , Franz Bryan A. , Frederikse Thomas , Fricker Helen A. , Frith Stacey M. , Froidevaux Lucien , Frost Gerald V. (JJ) , Fu Shanshan , Fu Yao , Füllekrug Martin , Ganter Catherine , Gao Meng , Garforth Judith , Garg Jay , Gerland Sebastian , Gevorgyan Artur , Giglio Donata , Gille Sarah T. , Gilson John , Gleason Karin , Gobron Nadine , Godin-Beekmann Sophie , Goes Marlos , Goldenberg Stanley B. , Gómez Camacho Julio , González Hernández Yolanda , Goodman Steven , Goto Atsushi , Graham Garrett , Grimm Alice , Grooß Jens-Uwe , Gruber Alexander , Gu Guojun , Guglielmin Mauro , Hahn Sebastian , Haimberger Leopold , Hakmi S. , Hall Brad D. , Hamlington Benjamin D. , Hanna Edward , Hanssen-Bauer Inger , Harlan Merritt E. , Harnos Daniel S. , Harris I. , He Qiong , Heatta Máret J. , Heim Richard R. Jr. , Hemming Deborah L. , Hendricks Stefan , Hicks J. , Hidalgo Hugo G. , Hirschi Martin , Ho Shu-peng (Ben) , Hobbs Will , Holzworth Robert , Horton Radley M. , Hrbáček Filip , Hu Guojie , Hu Zeng-Zhen , Huang Boyin , Huang Hongjie , Hurst Dale , Ialongo Iolanda , Inness Antje , Isaksen Ketil , Ishii Masayoshi , Jacox Michael G. , Jadra Gerardo , Jain Piyush , Jersild Annika , Jeuring Jelmer , Jevrejeva Svetlana , Jia Gensuo , John Viju O. , Johns William E. , Johnsen Bjørn , Johnson Bryan , Johnson Gregory C. , Jones P. D. , Josey Simon A. , Jumaux G. , Junod Robert , Kääb Andreas , Kabidi K. , Kaiser Johannes W. , Kaleschke Lars , Kaufmann Viktor , Kazemi Amin Fazl , Keller Linda M. , Kellerer-Pirklbauer Andreas , Kendon Michael , Kennedy John , Khalatyan Yelena , Khan Valentina , Khaykin Sergey , Khiem Mai Van , Kidd Richard , Killick Rachel E. , Kim Seong-Joong , King Tyler V. , Kipling Zak , Kirchmeier-Young Megan , Klotzbach Philip J. , Knaff John A. , Kohler Jack , Koppa Akash , Korshunova Natalia N. , Kraemer Benjamin M. , Kramarova Natalya A. , Kromer Jessica , Kruger A. C. , Kumar Arun , Kuusela Mikael , La Fuente R. Sofia , Laas Alo , Labe Zachary , Lader Rick , Lait Leslie , Lakatos Mónika , Lakkala Kaisa , Lam Hoang Phuc , Lan Xin , Landschützer Peter , Landsea Chris W. , Lantz Kathleen O. , Lapierre Jeff , Lara Mark J. , Lavado-Casimiro Waldo , Lavers David A. , Lazzara Matthew A. , Leblanc Thierry , Lee Simon H. , Lee Tsz-Cheung , Leibensperger Eric , Lennard Chris , Leuliette Eric , L’Heureux Michelle , Lieser Jan L. , Liley Ben , Lin I-I , Liu Chao , Liu Yakun , Lo Y. T. Eunice , Locarnini Ricardo , Loeb Norman G. , Loomis Bryant D. , Lopez Hosmay , Lorrey Andrew M. , Loyola Diego , Lozier Susan M. , Lu Rui , Luks Bartłomiej , Lumpkin Rick , Luo Jing-Jia , Luojus Kari , Lyman John M. , Macander Matthew J. , MacFerrin Michael , MacGilchrist Graeme M. , MacLennan Michelle L. , Magee Andrew D. , Magnin Florence , Magnússon Rúna Í. , Mamen Jostein , Mankoff Ken D. , Manney Gloria , Marengo Jose A. , Marjan Mohammadi , Marouchos Andreas , Martinez Rodney , Massom Robert A. , Matsuzaki Shin-Ichiro , Matthews Tom , Mayer Michael , McBride C. , McCarthy Michael , McMahon Clive R. , McVicar Tim R. , Mears Carl A. , Medley Brooke , Meier Walter N. , Mekonnen Ademe , Menzel Annette , Merchant Christopher J. , Merio Leo-Juhani , Merrifield Mark A. , Meyer Michael F. , Meyers Tristan , Mikolajczyk David E. , Miller John B. , Minney Caitlin , Miralles Diego G. , Mishonov Alexey , Mitchum Gary T. , Moat Ben I. , Moise Aurel , Molina-Carpio Jorge , Montesano Paul M. , Montzka Stephan A. , Moody Ronald , Moon Twila A. , Mora Natali , Morice Colin , Morino Isamu , Mostafa A. E. , Mote Thomas L. , Mrekaj Ivan , Mudryk Lawrence , Muharsyah Robi , Mühle Jens , Müller Rolf , Nance D. , Neigh Christopher S. R. , Nerem R. Steven , Newman Paul A. , Nicolas Julien P. , Noetzli Jeannette , Noll Ben , Norton Taylor , Nyland Kelsey E. , O’Keefe John , Oe Mitsuho , Okunaka Yuka , Orlik Alexander , Osborn Tim J. , Overland James E. , Pálsson Finnur , Parrington Mark , Pasch Richard J. , Pascual Ramírez Reynaldo , Paterson Linda , Pellet Cécile , Pelto Mauri S. , Perez Renellys C. , Perovich Donald K. , Petersen Kyle , Petropavlovskikh Irina , Petty Alek , Pezza Alexandre B. , Pezzi Luciano P. , Phillips Coda , Phoenix Gareth K. , Pierson Don , Pinto Izidine , Pita Ivenis , Pitts Michael , Po-Chedley Stephen , Pogliotti Paolo , Poinar Kristin , Polvani Lorenzo , Porat Amos , Preimesberger Wolfgang , Price Colin , Purkey Sarah G. , Quispe Willy R. , Ramos Andrea M. , Randel William J. , Raphael Marilyn N. , Raymond Colin , Reagan James , Reid Phillip , Rémy Samuel , Ressl Hans , Ricciardulli Lucrezia , Richardson Andrew D. , Ricker Robert , Rivera Patricia P. , Robinson David A. , Robjhon M. , Rodell Matthew , Rodriguez Guisado Esteban , Rodriguez-Fernandez Nemesio , Roebeling Maarit , Rogers Cassandra , Rohini P. , Romanovsky Vladimir E. , Ronchail Josyane , Rosencrans Matthew , Rosenlof Karen , Rösner Benjamin , Rozanov Alexei , Rozkošný Jozef , Rusanovskaya Olga O. , Rutishauser This , Sabeerali C. T. , Said Ryan , Sakai Tetsu , Salinas Roberto , Sánchez-Lugo Ahira , Santee Michelle L. , Sass Louis , Sato Kanako , Sawaengphokhai Parnchai , Sayouri A. , Scambos Theodore A. , Scheller Johan H. , Schenzinger Verena , Schlegel Robert W. , Schmid Claudia , Schmid Martin , Schreck Carl J. , Schulz Cristina , Segele Z. T. , Seneviratne Sonia I. , Sensoy Serhat , Seong Ji-In , Serna Cuenca Julieta , Serreze Mark C. , Sezaki Fumi , Shao Xi , Sharma Sapna , Shi Jia-Rui , Shi Lei , Shiklomanov Nikolay I. , Shimaraeva Svetlana V. , Shinohara Ryuichiro , Shukla R. , Silow Eugene A. , Simmons Adrian J. , Smeed David A. , Smith Adam , Smith Benjamin E. , Smith Ryan H. , Smith Sharon L. , Soden Brian J. , Sofieva Viktoria , Soldo Logan , Souza Everaldo , Spence-Hemmings Jacqueline , Spillane Sandra , Sreejith O. P. , Srivastava A. K. , Stackhouse Jr.Paul W. , Stammerjohn Sharon , Stauffer Ryan , Steinbrecht Wolfgang , Steiner Andrea K. , Stella Jose L. , Stephenson Tannecia S. , Stevens Laura , Stoy Paul , Stradiotti Pietro , Streletskiy Dmitry A. , Sukianto Thea , Svendby Tove , Sweet William , Taha Ghassan , Takahashi Kiyotoshi , Takemura Kazuto , Taylor Michael A. , Tedesco Marco , Thackeray Stephen J. , Thiaw W. M. , Thibert Emmanuel , Thomalla Sandy , Thoman Richard L. , Thompson Philip R. , Thomson Laura , Thorsteinsson Thorsteinn , Tian-Kunze Xiangshan , Timmermans Mary-Louise , Timofeyev Maxim A. , Tømmervik Hans , Tourpali Kleareti , Trachte Katja , Trewin Blair C. , Triñanes Joaquin A. , Tripathy Sarat Chandra , Tronquo Emma , Trotman Adrian , Truchelut Ryan E. , Trusel Luke D. , Turner Katherine , Tye Mari R. , Uehling John , van der A Ronald , van der Linden Roderick , van der Schalie Robin , van der Schrier Gerard , Van Meerbeeck Cédric J. , van Vliet Arnold J. H. , Vazife Ahad , Verburg Piet , Vernier Jean-Paul , Vimont Isaac J. , Virasami R. , Virts Katrina , Vivero Sebastián , Volkov Denis L. , Vömel Holger , Vose Russell S. , Waigl Christine F. , Walker Donald (Skip) A. , Walsh John E. , Wang Bin , Wang Hui , Wang Muyin , Wang Ray H. J. , Wanninkhof Rik , Warnock Taran , Weber Mark , Webster Melinda , Wehrlé Adrian , Weller Robert A. , Westberry Toby K. , Widlansky Matthew J. , Wiese David N. , Wild Jeannette D. , Willett Kate M. , Williams Earle , Willis Josh K. , Wolken Gabriel J. , Wong Takmeng , Wood Kimberly M. , Woolway Richard Iestyn , Wouters Bert , Wu Francis , Yang Dedi , Yin Xungang , Yin Ziqi , Yu Lisan , Zeng Zhenzhong , Zhang Huai-min , Zhang Peiqun , Zhao Lin , Zhong Feng , Zhu Zhiwei , Ziemke Jerry R. , Ziese Markus , Zotta Ruxandra M. , Zou Cheng-Zhi 
Published: August 2024

—J. Blunden and T. Boyer

In 2023, La Niña conditions that generally prevailed in the eastern Pacific Ocean from mid-2020 into early 2023 gave way to a strong El Niño by October. Atmospheric concentrations of Earth’s major greenhouse gases—carbon dioxide, methane, and nitrous oxide—all increased to record-high levels. The annual global average carbon dioxide concentration in the atmosphere rose to 419.3±0.1 ppm, which is 50% greater than the pre-industrial level. The growth from 2022 to 2023 was 2.8 ppm, the fourth highest in the record since the 1960s.

The combined short-term effects of El Niño and the long-term effects of increasing levels of heat-trapping gases in the atmosphere contributed to new records for many essential climate variables reported here. The annual global temperature across land and oceans was the highest in records dating as far back as 1850, with the last seven months (June–December) having each been record warm. Over land, the globally averaged temperature was also record high. Dozens of countries reported record or near-record warmth for the year, including China and continental Europe as a whole (warmest on record), India and Russia (second warmest), and Canada (third warmest). Intense and widespread heatwaves were reported around the world. In Vietnam, an all-time national maximum temperature record of 44.2°C was observed at Tuong Duong on 7 May, surpassing the previous record of 43.4°C at Huong Khe on 20 April 2019. In Brazil, the air temperature reached 44.8°C in Araçuaí in Minas Gerais on 20 November, potentially a new national record and 12.8°C above normal.

The effect of rising temperatures was apparent in the cryosphere, where snow cover extent by June 2023 was the smallest in the 56-year record for North America and seventh smallest for the Northern Hemisphere overall. Heatwaves contributed to the greatest average mass balance loss for Alpine glaciers around the world since the start of the record in 1970. Due to rapid volume loss beginning in 2021, St. Anna Glacier in Switzerland and Ice Worm Glacier in the United States disappeared completely. In August, as a direct result of glacial thinning over the past 20 years, a glacial lake on a tributary of the Mendenhall Glacier in Alaska burst through its ice dam and caused unprecedented flooding on Mendenhall River near Juneau.

Across the Arctic, the annual surface air temperature was the fourth highest in the 124-year record, and summer (July–September) was record warm. Smaller-than-normal snow cover extent in May and June contributed to the third-highest average peak tundra greenness in the 24-year record. In September, Arctic minimum sea ice extent was the fifth smallest in the 45-year satellite record. The 17 lowest September extents have all occurred in the last 17 years.

In Antarctica, temperatures for much of the year were up to 6°C above average over the Weddell Sea and along coastal Dronning Maud Land. The Antarctic Peninsula also experienced well-above-average temperatures during the 2022/23 melt season, which contributed to its fourth consecutive summer of above-average surface melt. On 21 February, Antarctic sea ice extent and sea ice area both reached all-time lows, surpassing records set just a year earlier. Over the course of the year, new daily record-low sea ice extents were set on 278 days. In some instances, these daily records were set by a large margin, for example, the extent on 6 July was 1.8 million km2 lower than the previous record low for that day.

Across the global oceans, the annual sea surface temperature was the highest in the 170-year record, far surpassing the previous record of 2016 by 0.13°C. Daily and monthly records were set from March onward, including an historic-high daily global mean sea surface temperature of 18.99°C recorded on 22 August. Approximately 94% of the ocean surface experienced at least one marine heatwave in 2023, while 27% experienced at least one cold spell. Globally averaged ocean heat content from the surface to 2000-m depth was record high in 2023, increasing at a rate equivalent to ∼0.7 Watts per square meter of energy applied over Earth’s surface. Global mean sea level was also record high for the 12th consecutive year, reaching 101.4 mm above the 1993 average when satellite measurements began, an increase of 8.1±1.5 mm over 2022 and the third highest year-over-year increase in the record.

A total of 82 named tropical storms were observed during the Northern and Southern Hemispheres’ storm seasons, below the 1991–2020 average of 87. Hurricane Otis became the strongest landfalling hurricane on record for the west coast of Mexico at 140 kt (72 m s−1), causing at least 52 fatalities and $12–16 billion U.S. dollars in damage. Freddy became the world’s longest-lived tropical cyclones on record, developing into a tropical cyclone on 6 February and finally dissipating on 12 March. Freddy crossed the full width of the Indian Ocean and made one landfall in Madagascar and two in Mozambique. In the Mediterranean Sea—outside of traditional tropical cyclone basins—heavy rains and flooding from Storm Daniel killed more than 4300 people and left more than 8000 missing in Libya.

The record-warm temperatures in 2023 created conditions that helped intensify the hydrological cycle. Measurements of total-column water vapor in the atmosphere were the highest on record, while the fraction of cloud area in the sky was the lowest since records began in 1980. The annual global mean precipitation total over land surfaces for 2023 was among the lowest since 1979, but global one-day maximum totals were close to average, indicating an increase in rainfall intensity.

In July, record-high areas of land across the globe (7.9%) experienced extreme drought, breaking the previous record of 6.2% in July 2022. Overall, 29.7% of land experienced moderate or worse categories of drought during the year, also a record. Mexico reported its driest (and hottest) year since the start of its record in 1950. In alignment with hot and prolonged dry conditions, Canada experienced its worst national wildfire season on record. Approximately 15 million hectares burned across the country, which was more than double the previous record from 1989. Smoke from the fires were transported far into the United States and even to western European countries. August to October 2023 was the driest three-month period in Australia in the 104-year record. Millions of hectares of bushfires burned for weeks in the Northern Territory. In South America, extreme drought developed in the latter half of the year through the Amazon basin. By the end of October, the Rio Negro at Manaus, a major tributary of the Amazon River, fell to its lowest water level since records began in 1902.

The transition from La Niña to El Niño helped bring relief to the prolonged drought conditions in equatorial eastern Africa. However, El Niño along with positive Indian Ocean dipole conditions also contributed to excessive rainfall that resulted in devastating floods over southeastern Ethiopia, Somalia, and Kenya during October to December that displaced around 1.5 million people. On 5 September, the town of Zagora, Greece, broke a national record for highest daily rainfall (754 mm in 21 hours, after which the station ceased reporting) due to Storm Daniel; this one-day accumulation was close to Zagora’s normal annual total.