Description: 〈jats:title〉Abstract〈/jats:title〉 〈jats:p〉—J. BLUNDEN, T. BOYER, AND E. BARTOW-GILLIES〈/jats:p〉 〈jats:p〉Earth’s global climate system is vast, complex, and intricately interrelated. Many areas are influenced by global-scale phenomena, including the “triple dip” La Niña conditions that prevailed in the eastern Pacific Ocean nearly continuously from mid-2020 through all of 2022; by regional phenomena such as the positive winter and summer North Atlantic Oscillation that impacted weather in parts the Northern Hemisphere and the negative Indian Ocean dipole that impacted weather in parts of the Southern Hemisphere; and by more localized systems such as high-pressure heat domes that caused extreme heat in different areas of the world. Underlying all these natural short-term variabilities are long-term climate trends due to continuous increases since the beginning of the Industrial Revolution in the atmospheric concentrations of Earth’s major greenhouse gases.〈/jats:p〉 〈jats:p〉In 2022, the annual global average carbon dioxide concentration in the atmosphere rose to 417.1±0.1 ppm, which is 50% greater than the pre-industrial level. Global mean tropospheric methane abundance was 165% higher than its pre-industrial level, and nitrous oxide was 24% higher. All three gases set new record-high atmospheric concentration levels in 2022.〈/jats:p〉 〈jats:p〉Sea-surface temperature patterns in the tropical Pacific characteristic of La Niña and attendant atmospheric patterns tend to mitigate atmospheric heat gain at the global scale, but the annual global surface temperature across land and oceans was still among the six highest in records dating as far back as the mid-1800s. It was the warmest La Niña year on record. Many areas observed record or near-record heat. Europe as a whole observed its second-warmest year on record, with sixteen individual countries observing record warmth at the national scale. Records were shattered across the continent during the summer months as heatwaves plagued the region. On 18 July, 104 stations in France broke their all-time records. One day later, England recorded a temperature of 40°C for the first time ever. China experienced its second-warmest year and warmest summer on record. In the Southern Hemisphere, the average temperature across New Zealand reached a record high for the second year in a row. While Australia’s annual temperature was slightly below the 1991–2020 average, Onslow Airport in Western Australia reached 50.7°C on 13 January, equaling Australia's highest temperature on record.〈/jats:p〉 〈jats:p〉While fewer in number and locations than record-high temperatures, record cold was also observed during the year. Southern Africa had its coldest August on record, with minimum temperatures as much as 5°C below normal over Angola, western Zambia, and northern Namibia. Cold outbreaks in the first half of December led to many record-low daily minimum temperature records in eastern Australia.〈/jats:p〉 〈jats:p〉The effects of rising temperatures and extreme heat were apparent across the Northern Hemisphere, where snow-cover extent by June 2022 was the third smallest in the 56-year record, and the seasonal duration of lake ice cover was the fourth shortest since 1980. More frequent and intense heatwaves contributed to the second-greatest average mass balance loss for Alpine glaciers around the world since the start of the record in 1970. Glaciers in the Swiss Alps lost a record 6% of their volume. In South America, the combination of drought and heat left many central Andean glaciers snow free by mid-summer in early 2022; glacial ice has a much lower albedo than snow, leading to accelerated heating of the glacier. Across the global cryosphere, permafrost temperatures continued to reach record highs at many high-latitude and mountain locations.〈/jats:p〉 〈jats:p〉In the high northern latitudes, the annual surface-air temperature across the Arctic was the fifth highest in the 123-year record. The seasonal Arctic minimum sea-ice extent, typically reached in September, was the 11th-smallest in the 43-year record; however, the amount of multiyear ice—ice that survives at least one summer melt season—remaining in the Arctic continued to decline. Since 2012, the Arctic has been nearly devoid of ice more than four years old.〈/jats:p〉 〈jats:p〉In Antarctica, an unusually large amount of snow and ice fell over the continent in 2022 due to several landfalling atmospheric rivers, which contributed to the highest annual surface mass balance, 15% to 16% above the 1991–2020 normal, since the start of two reanalyses records dating to 1980. It was the second-warmest year on record for all five of the long-term staffed weather stations on the Antarctic Peninsula. In East Antarctica, a heatwave event led to a new all-time record-high temperature of −9.4°C—44°C above the March average—on 18 March at Dome C. This was followed by the collapse of the critically unstable Conger Ice Shelf. More than 100 daily low sea-ice extent and sea-ice area records were set in 2022, including two new all-time annual record lows in net sea-ice extent and area in February.〈/jats:p〉 〈jats:p〉Across the world’s oceans, global mean sea level was record high for the 11th consecutive year, reaching 101.2 mm above the 1993 average when satellite altimetry measurements began, an increase of 3.3±0.7 over 2021. Globally-averaged ocean heat content was also record high in 2022, while the global sea-surface temperature was the sixth highest on record, equal with 2018. Approximately 58% of the ocean surface experienced at least one marine heatwave in 2022. In the Bay of Plenty, New Zealand’s longest continuous marine heatwave was recorded.〈/jats:p〉 〈jats:p〉A total of 85 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, close to the 1991–2020 average of 87. There were three Category 5 tropical cyclones across the globe—two in the western North Pacific and one in the North Atlantic. This was the fewest Category 5 storms globally since 2017. Globally, the accumulated cyclone energy was the lowest since reliable records began in 1981. Regardless, some storms caused massive damage. In the North Atlantic, Hurricane Fiona became the most intense and most destructive tropical or post-tropical cyclone in Atlantic Canada’s history, while major Hurricane Ian killed more than 100 people and became the third costliest disaster in the United States, causing damage estimated at $113 billion U.S. dollars. In the South Indian Ocean, Tropical Cyclone Batsirai dropped 2044 mm of rain at Commerson Crater in Réunion. The storm also impacted Madagascar, where 121 fatalities were reported.〈/jats:p〉 〈jats:p〉As is typical, some areas around the world were notably dry in 2022 and some were notably wet. In August, record high areas of land across the globe (6.2%) were experiencing extreme drought. Overall, 29% of land experienced moderate or worse categories of drought during the year. The largest drought footprint in the contiguous United States since 2012 (63%) was observed in late October. The record-breaking megadrought of central Chile continued in its 13th consecutive year, and 80-year record-low river levels in northern Argentina and Paraguay disrupted fluvial transport. In China, the Yangtze River reached record-low values. Much of equatorial eastern Africa had five consecutive below-normal rainy seasons by the end of 2022, with some areas receiving record-low precipitation totals for the year. This ongoing 2.5-year drought is the most extensive and persistent drought event in decades, and led to crop failure, millions of livestock deaths, water scarcity, and inflated prices for staple food items.〈/jats:p〉 〈jats:p〉In South Asia, Pakistan received around three times its normal volume of monsoon precipitation in August, with some regions receiving up to eight times their expected monthly totals. Resulting floods affected over 30 million people, caused over 1700 fatalities, led to major crop and property losses, and was recorded as one of the world’s costliest natural disasters of all time. Near Rio de Janeiro, Brazil, Petrópolis received 530 mm in 24 hours on 15 February, about 2.5 times the monthly February average, leading to the worst disaster in the city since 1931 with over 230 fatalities.〈/jats:p〉 〈jats:p〉On 14–15 January, the Hunga Tonga-Hunga Ha'apai submarine volcano in the South Pacific erupted multiple times. The injection of water into the atmosphere was unprecedented in both magnitude—far exceeding any previous values in the 17-year satellite record—and altitude as it penetrated into the mesosphere. The amount of water injected into the stratosphere is estimated to be 146±5 Terragrams, or ∼10% of the total amount in the stratosphere. It may take several years for the water plume to dissipate, and it is currently unknown whether this eruption will have any long-term climate effect.〈/jats:p〉

Description: The densest waters in the deep limb of the Atlantic meridional overturning circulation (AMOC) consist of overflow waters from the Nordic Seas: Denmark Strait Overflow Water (DSOW) and Iceland-Scotland Overflow Water (ISOW). These overflow waters are then substantially modified along their pathways by the entrainment of overlying intermediate waters and are eventually exported from the sub-polar gyre as Lower North Atlantic Deep Water. Since 2014, the OSNAP array has provided new insights into the sub-polar overturning circulation, including key boundary current arrays deployed across the Reykjanes Ridge, off East and West Greenland, and along the western side of the Labrador Sea. Here, using the OSNAP array data between 2014 and 2020, we quantify the mean transports of overflow waters along the deep boundary pathways, as well as recirculation within the Labrador Sea and Irminger Basin. Changes in the water properties of ISOW and DSOW as they advect around the deep subpolar gyre are also assessed. We further examine the traditional use of potential density of 27.88 kg/m〈sup〉3〈/sup〉 as the interface between ISOW and DSOW, and assess whether water mass boundary definitions need to change with increasing distance and entrainment along the deep circulation pathways.

Description: The meridional heat transport (MHT) estimated at 26N in the Atlantic Ocean as part of the RAPID-MOCHA project is one of the prominent observable oceanic indices of the global climate. Understanding the linear relationship between the MHT and other global climate indicators is important for improving our understanding of climate dynamics and providing benchmarks for assessing earth system reanalysis products. The MHT time series exhibits significant correlation with various climate indices but the dynamical interpretation of these correlations is difficult since these indices are typically correlated among themselves. To clarify the implications of these correlations, we investigate the regression patterns between the MHT and field variables from the ERA5 monthly reanalysis dataset. We use a method that allows us to decompose these regression patterns into statistically significant spatio-temporal components that can be subsequently linked to known global climate indices. Our preliminary results suggest that up to 40% of the monthly variance of the MHT can be linearly attributed to three global modes. These modes, explaining 19, 13, and 8 percent of the MHT variance, are respectively strongly related to the Arctic Oscillation index, the Southern Oscillation index, and the Antarctic Oscillation index, which are three indices uncorrelated with each other. Yet, each of these three modes exhibits air-sea heat flux and 2-m atmospheric temperature patterns over northern hemisphere latitudes that are markedly different. This implies that the net impacts on regional climates of MHT changes at any time can vary depending on the global state of the climate system.

Description: The system of oceanic flows constituting the Atlantic Meridional Overturning Circulation (AMOC) moves heat and other properties to the subpolar North Atlantic, controlling regional climate, weather, sea levels, and ecosystems. Climate models suggest a potential AMOC slowdown towards the end of the 21〈sup〉st〈/sup〉 century due to anthropogenic forcing, which would accelerate coastal sea level rise along the western boundary and dramatically increase coastal flood risk. While the slowdown has not been observed to date, we show here that the AMOC-induced intrinsic changes in gyre-scale heat content, superimposed on the global mean sea level rise, are already influencing the frequency of floods along the United States southeastern seaboard. For the South Atlantic Bight and Gulf of Mexico coasts, using observations and an ocean state estimate, we have established a strong link between coastal sea level, the associated flood frequency, and gyre-scale dynamic sea level and oceanic heat content variability, which are largely controlled by AMOC-driven ocean heat convergence. We find that ocean heat convergence, being the primary driver for interannual sea level changes in the subtropical North Atlantic, has led to an exceptional gyre-scale warming and associated dynamic sea level rise since 2010, accounting for 30-50% of flood days in 2015-2020. The results of this study highlight the importance of accounting for natural, large-scale sea level variability in order to improve coastal sea level projections and to better assess coastal flood risk.

Description: The time series of the Atlantic Meridional Overturning Circulation (AMOC) at 26°N has been extended to December 2020 and is close to 17 years long. During the period from 2004 to 2008 the AMOC was about 2.5 Sv stronger than in the following years. Since then, there has been significant interannual variability, but the AMOC has remained relatively weak compared with the first four years of observations. The design of the array was changed in 2020 so that continuous measurements are no longer made over the mid-Atlantic Ridge and in the deep eastern basin. Instead, it is proposed to use data from quinquennial hydrographic surveys to quantify changes in these locations. Here, the extended time series is presented and the impact of the design change on the accuracy of the RAPID timeseries is examined. Other possible design changes are considered too. It is shown that, although the mid-Atlantic ridge measurements have been important in determining the mean structure of the overturning streamfunction, the impact upon the variability of the streamfunction maximum has been small. It is hoped that these changes will enable the measurement of the AMOC at 26°N to be sustained in the future.

Description: Simultaneous mooring arrays were maintained along the path of the Equatorial Undercurrent (EUC) at three longitudes (23°W, 10°W, and 0°E), from October 2007 to June 2011, as part of the CLIVAR Tropical Atlantic Climate Experiment. The measurements allow for the first time a description of the seasonal cycle and interannual variability of the EUC across the Atlantic basin. The mean transport of the EUC at 23°W is 14.3 ± 0.6 Sv, decreasing to 12.1 ± 0.9 and 9.4 ± 0.6 Sv at 10°W and 0°E, respectively. The EUC shows a changing seasonal cycle across the basin: at 23°W, the strongest EUC transport occurs in boreal fall in association with maximum easterly wind stress, at 10°W the EUC transport shows a semiannual cycle with a maximum in boreal spring and fall, while at 0°E the EUC has a single spring maximum. At all locations the EUC core exhibits a similar seasonal vertical migration, with shallowest core depths occurring in boreal spring and deepest core depths in boreal fall. The maximum core intensity occurs in boreal spring all across the basin, when the EUC is shallow, during the annual wind relaxation. The weakest EUC core intensity occurs during the boreal summer cold tongue phase, especially in the eastern part of the basin. At both 23°W and 10°W, a deep extension of the EUC occurs in boreal summer, which increases the transport in the lower thermocline and partially offsets the weaker upper EUC transport during boreal summer. No clear linkage could be established between the interannual variability of the EUC in the eastern part of the basin and the intensity of the summer cold tongue, despite evidence for such a linkage in the western part of the basin.

Description: The Atlantic meridional overturning circulation (AMOC) makes the strongest oceanic contribution to the meridional redistribution of heat. Here, an observation-based, forty-eight-month-long time series of the vertical structure and strength of the AMOC at 26.5°N is presented. From April 2004 to April 2008 the AMOC had a mean strength of 18.7 ±2.1 Sv with fluctuations of 4.8 Sv rms. The best guess of the peak-to-peak amplitude of the AMOC seasonal cycle is 6.7 Sv, with a maximum strength in autumn and a minimum in spring. While seasonality in the AMOC was commonly thought to be dominated by the northward Ekman transport, this study reveals that fluctuations of the geostrophic mid-ocean and Gulf Stream transports of 2.2 Sv and 1.7 Sv rms, respectively, are substantially larger than those of the Ekman component (1.2 Sv rms). A simple model based on linear dynamics suggests that the seasonal cycle is dominated by wind stress curl forcing at the eastern boundary of the Atlantic. Seasonal geostrophic AMOC anomalies might represent an important and previously underestimated component of meridional transport and storage of heat in the subtropical North Atlantic. There is evidence that the seasonal cycle observed here is representative of much longer intervals. Previously, hydrographic snapshot estimates between 1957 and 2004 had suggested a long-term decline of the AMOC by 8 Sv. This study suggests that aliasing of seasonal AMOC anomalies might have accounted for a large part of the inferred slowdown.