Another Record: Ocean Warming Continues through 2021 despite La Niña Conditions

ADVANCES IN ATMOSPHERIC SCIENCES, 2022 • Original Paper • Another Record: Ocean Warming Continues through 2021 despite La Niña Conditions Lijing CHENG*1,2, John ABRAHAM3, Kevin E. TRENBERTH4, John FASULLO4, Tim BOYER5, Michael E. MANN6, Jiang ZHU1,2, Fan WANG2,7, Ricardo LOCARNINI5, Yuanlong LI2,7, Bin ZHANG2,7, Zhetao TAN1,2, Fujiang YU8, Liying WAN8, Xingrong CHEN8, Xiangzhou SONG9, Yulong LIU10, Franco RESEGHETTI11, Simona SIMONCELLI12, Viktor GOURETSKI1, Gengxin CHEN13, Alexey MISHONOV5,14, and Jim REAGAN5 1International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 2Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China 3University of St. Thomas, School of Engineering, Minnesota 55105, USA 4National Center for Atmospheric Research, Boulder, Colorado 80307, USA 5National Oceanic and Atmospheric Administration, National Centers for Environmental Information, Silver Spring, Maryland 20910, USA 6Department of Meteorology & Atmospheric Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA 7Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China 8National Marine Environmental Forecasting Center, Ministry of Natural Resources of China, Beijing 100081, China 9College of Oceanography, Hohai University, Nanjing 210098, China 10National Marine Data and Information Service, Tianjin 300171, China 11Italian National Agency for New Technologies, Energy and Sustainable Economic Development, S. Teresa Research Center, Lerici 19032, Italy 12Istituto Nazionale di Geofisica e Vulcanologia, Sede di Bologna, Bologna 40128, Italy 13South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China 14ESSIC/CISESS-MD, University of Maryland, College Park, MD 20742, USA (Received 19 December 2021; revised 8 January 2022; accepted 10 January 2022) ABSTRACT The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year’s record value by 14 ± 11 ZJ (1 zetta J = 1021 J) using the IAP/CAS dataset and by 16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Niño-Southern Oscillation (ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans, and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation. Key words: La Niña, ocean heat, ocean warming, attribution, observation Citation: Cheng, L. J, and Coauthors, 2022: Another record: Ocean warming continues through 2021 despite La Niña conditions. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-022-1461-3. * Corresponding author: Lijing CHENG Email: © The Author(s) 2022. This article is published with open access at link.springer.com 2 RECORD OCEAN WARMING IN 2021 Article Highlights: • The world ocean, in 2021, was the hottest ever recorded by humans. • The warming pattern is mainly attributed to increased anthropogenic greenhouse gas concentrations, offset by the impact of aerosols. • Ocean warming has far-reaching consequences and should be incorporated into climate risk assessments, adaptation, and mitigation. 1. Introduction The increased concentrations of greenhouse gases in the atmosphere from human activities trap heat within the climate system and result in massive changes in the climate system. As a result, outgoing energy from the Earth system is not balancing the incoming solar radiation, thus creating Earth’s Energy Imbalance (EEI) in the climate system (Trenberth et al., 2014; von Schuckmann et al., 2016a, 2020a; Wijffels et al., 2016; Johnson et al., 2018; Cheng et al., 2019a). The oceans store over 90% of EEI, leading to an increase of ocean heat content (OHC), which currently provides the best estimate for EEI (Hansen et al., 2011; IPCC, 2013; Rhein et al., 2013; Trenberth et al., 2016; Abram et al., 2019). Ocean warming leads to increased ocean vertical stratification, thermal expansion, and sealevel rise. These processes provide a compelling means to quantify climate change (Cheng et al., 2018). This study provides the first analysis of recent OHC changes through 2021. Two international data products include those from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences (CAS) (Cheng et al., 2017) and the National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA) (Levitus et al., 2012). Both datasets corrected systematic errors and then used thorough mapping methods to convert discrete ocean measurements into a comprehensive picture of the ocean. Both global and regional analyses of OHC changes are provided in this study. 2. Data and Methods The IAP/CAS and NCEI/NOAA analyses are based on available in situ observations from various measurement devices held in the World Ocean Database (WOD) of the NCEI/NOAA. Data from all instruments are used, including eXpendable BathyThermographs (XBTs), profiling floats from Argo, moorings, gliders, Conductivity/Temperature/Depth devices (CTDs), bottles, and instruments on marine mammals (Boyer et al., 2018). The XBT biases are corrected according to Cheng et al. (2014) for IAP/CAS and Levitus et al. (2009) for NCEI/NOAA. Model simulations guide the mapping method from point measurements to the comprehensive grid in the IAP/CAS product. At the same time, sampling errors are estimated by sub-sampling the Argo data at the locations of the earlier observations (a full description of the method is in Cheng et al., 2017). The Argo Program is part of the Global Ocean Observing System. The Argo observing network achieved a near-global upper-2000 m coverage since about 2005 (Argo, 2020). Argo data are made freely available by the International Argo Program and the contributing national programs (http://www.argo.ucsd.edu; http://argo.jcommops. org). In addition to these observations, the Community Earth System Model Version 1 (CESM1) Large Ensemble (LENS; Kay et al., 2015) data are used to explore the influence of different forcings (aerosols, greenhouse gasses, industrial aerosols, biomass ae (...truncated)