2018 Continues Record Global Ocean Warming

ADVANCES IN ATMOSPHERIC SCIENCES, VOL. 36, MARCH 2019, 249–252 • News & Views • 2018 Continues Record Global Ocean Warming Lijing CHENG∗1 , Jiang ZHU1 , John ABRAHAM2 , Kevin E. TRENBERTH3 , John T. FASULLO3 , Bin ZHANG4,5 , Fujiang YU6 , Liying WAN6 , Xingrong CHEN6 , and Xiangzhou SONG7,8 1 International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 2 University 3 National 4 Institute 5 Center 6 National of St. Thomas, School of Engineering, Minnesota 55105, USA Center for Atmospheric Research, Boulder, Colorado 80307, USA of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China Marine Environmental Forecasting Center, Ministry of Natural Resources of China, Beijing 100081, China 7 College 8 Bureau of Oceanography, Hohai University, Nanjing 210098, China of Territorial and Spatial Planning, Ministry of Natural Resources, Beijing 100812, China (Received 24 December 2018; revised 7 January 2019; accepted 8 January 2019) Citation: Cheng, L J., and Coauthors, 2019: 2018 continues record global ocean warming. Adv. Atmos. Sci., 36(3), 249–252, https://doi.org/10.1007/s00376-019-8276-x. The increasing heat-trapping gases emitted by human activities into the atmosphere produce an energy imbalance between incoming solar radiation and outgoing longwave radiation that leads to global heating (Rhein et al., 2013; Trenberth et al., 2014; von Schuckmann et al., 2016). The vast majority of global warming heat ends up deposited in the world’s oceans, and ocean heat content (OHC) change is one of the best—if not the best—metric for climate change (Cheng et al., 2019). In 2018, continued record heat was measured in the Earth’s climate system. In fact, 2018 has set a new record of ocean heating, surpassing 2017, which was the previous warmest year ever recorded (Cheng et al., 2018) (Fig. 1). Based on the new update of the Institute of Atmospheric Physics (IAP) ocean analysis (see “Data and methods” section), the total ocean heat anomaly in 2018, relative to a 1981–2010 baseline, and for the upper 2000 m of the world’s oceans, is (19.67 ± 0.83) × 1022 J. This level of thermal energy places 2018 as the hottest year ever recorded. Figure 1 shows the progression of upper 2000 m OHC since the late 1950s. The ranking of the five warmest years (Table 1) makes the past five years the warmest years on record. This supports the provisional announcement by the World Meteorological Organization in November 2018 that “the ocean heat content was the highest or 2nd highest on record”. And the new record in 2018 confirms the perspective (Cheng et al., 2019) that ocean warming continues and has been accelerating since the 1990s (compared with 1960 to the 1980s). The heating was distributed throughout the world’s oceans, with the vast majority of regions showing an increase in thermal energy (Fig. 1). The Southern Ocean (south of 30◦ S) and Pacific Ocean showed more warming than the Atlantic Ocean and Indian Ocean (Shi et al., 2018; Swart et al., 2018). The Southern Ocean and Pacific Ocean (north of 30◦ S) were (6.91 ± 1.70) × 1022 and (5.97 ± 1.07) × 1022 J above the 1981–2010 period, respectively. In comparison, the values for the Atlantic Ocean (north of 30◦ S) and Indian Ocean (north of 30◦ S) were (4.95 ± 1.97) × 1022 and (1.84 ± 1.97) × 1022 J. The spatial pattern also indicates some imprints of internal variability in the climate system (Cheng et al., 2018). For example, in 2018, the tropical Pacific transformed from a La Niña state in the early part of the year into a weak El Niño condition later (see “Data and methods” section). The heat was recharged in the equatorial regions within 10◦ S–5◦ N (Fig. 1), leaving negative OHC anomalies in the north subtropical Pacific Ocean (5◦ –15◦ N). The Indian Ocean continued its rapid warming trend since the 1990s, partly linked to both anthropogenic forcing and the Pacific Decadal Oscillation (Li et al., 2018). Increases in ocean heat are incontrovertible proof that the Earth is warming (Fig. 1). The long-term trend of ocean heat is a major concern both in the scientific community and for the public at large. The increased temperatures cause a thermal expansion of water and a rise in sea level (Nerem et al., 2018; WCRP Global Sea Level Budget Group, 2018). The increase in ocean heat of (19.67 ± 0.83) × 1022 J in 2018 resulted in a 29.5 mm global mean sea level rise above the 1981–2010 average, and 1.4 mm above 2017. The resulting sea level rise exposes coastal freshwater supplies to saltwater intrusion, makes communities ∗ Corresponding author: Lijing CHENG Email: 250 VOLUME 36 Global ocean heat content change in the upper 2000 m 20 15 10 22 (10 J) 5 Annual mean 0 Annual mean -5 -10 Monthly mean -15 95% error bar Baseline 1981-2010 -20 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2018 ocean heat content anomaly at upper 2000m (10 9 J m -2 ) 80N 40N 0 40S 80S 60 E -4 -3 -2 120 E -1 180 120 W 0 60W 1 Baseline 1981-2010 0 2 3 4 Fig. 1. Upper panel: Change in 0–2000 m OHC from 1958 to 2018. Each bar shows the annual mean relative to a 1981–2010 baseline (positive in red and negative in blue). The green error bar indicates the 95% confidence interval, and the black line is the monthly time series. Lower panel: Annual mean OHC anomaly for the upper 2000 m in 2018 relative to a 1981–2010 baseline. Units: 109 J m−2 . Source: IAP ocean analysis. Table 1. Top five warmest years in the ocean since 1958. The OHC values in the upper 2000 m are the anomalies (units: J) relative to the 1981–2010 average. Rank Year OHC (J) 1 2 3 4 5 2018 2017 2015 2016 2014 19.67 ± 0.83 × 1022 18.76 ± 0.80 × 1022 17.99 ± 0.70 × 1022 17.47 ± 0.76 × 1022 16.22 ± 0.70 × 1022 more susceptible to storm surges, and threatens coastal infrastructure. The current sea level and its associated pattern is expected to continue and accelerate in the near future (Fasullo et al., 2018). The increase in ocean heat (Fig. 1) also affects the planet’s weather systems, by raising air temperatures and supplying more moisture; warmer air can hold more moisture at a rate of about 7% ◦ C−1 (Trenberth, 2011). In turn, this leads to increases in the intensity of storms and heavy rains (Patricola and Wehner, 2018; Trenberth et al., 2018). In 2018, the world experienced a number of major tropical storms, some of which developed very rapidly and many caused death and destruction. These included hurricanes Florence and Michael in the Atlantic, and major typhoons Jebi, Maria, Manghut and Trami in the 251 MARCH 2019 Pacific. Typhoon Mangkhut was the planet’s most intense storm of 2018, with winds of 287 km h−1 ; it caused huge damage in Hong Kong. Several of these storms caused major flooding, especially Florence in the Carolinas. Other storms also led to major flooding events in Japan in (...truncated)