The year 2021 began with an episode of cold phase El Niño Southern Oscillation (ENSO) episode, also known as La Niña, across the central and eastern tropical Pacific Ocean, which had developed in August 2020. As seen in the graph below, ENSO can have an effect on global temperatures. La Niña episodes tend to cool global temperatures slightly, while the warm phase ENSO (also known as El Niño) tends to boost global temperatures. Although the monthly global temperatures were above average throughout the year, February 2021 was the coldest month of 2021 for the globe. The global temperature departure for February 2021 was +0.64°C (+1.15°F) — the coolest February since 2014. However, after the month of February, temperatures were at 0.80°C (1.44°F) or higher for the remaining months of 2021.
The year culminated as the sixth warmest year on record for the globe with a temperature that was 0.84°C (1.51°F) above the 20th century average. The years 2013–2021 all rank among the ten warmest years on record. The year 2021 was also the 45th consecutive year (since 1977) with global temperatures, at least nominally, above the 20th century average. Of note, the year 2005, which was the first year to set a new global temperature record in the 21st century, currently ties with 2013 as the 10th warmest year on record and 2010 ranks as the ninth warmest on record. Overall, the global annual temperature has increased at an average rate of 0.08°C (0.14°F) per decade since 1880 and over twice that rate (0.18°C / 0.32°F) since 1981.
The 2021 Northern Hemisphere surface temperature was also the sixth highest on record. However, the land portion of the Northern Hemisphere had a temperature that was 1.54°C (2.77°F) above average and the third highest in the 142-year record. Only the years of 2016 (second warmest) and 2020 (warmest) were warmer. Meanwhile, the Southern Hemisphere had its ninth warmest year on record.
(out of 142 years)
|Land||+1.35 ± 0.14||+2.43 ± 0.25||Warmest||6th||2020||+1.58||+2.84|
|Ocean||+0.65 ± 0.16||+1.17 ± 0.29||Warmest||7th||2016||+0.80||+1.44|
|Land and Ocean||+0.84 ± 0.15||+1.51 ± 0.27||Warmest||6th||2016||+0.99||+1.78|
|Land||+1.54 ± 0.16||+2.77 ± 0.29||Warmest||3rd||2020||+1.74||+3.13|
|Ocean||+0.81 ± 0.16||+1.46 ± 0.29||Warmest||7th||2020||+0.99||+1.78|
|Land and Ocean||+1.09 ± 0.15||+1.96 ± 0.27||Warmest||6th||2020||+1.27||+2.29|
|Land||+0.86 ± 0.11||+1.55 ± 0.20||Warmest||12th||2019||+1.29||+2.32|
|Ocean||+0.54 ± 0.16||+0.97 ± 0.29||Warmest||7th||2016||+0.70||+1.26|
|Land and Ocean||+0.59 ± 0.15||+1.06 ± 0.27||Warmest||9th||2016||+0.77||+1.39|
The 1901–2000 average combined land and ocean annual temperature is 13.9°C (57.0°F), the annually averaged land temperature for the same period is 8.5°C (47.3°F), and the long-term annually averaged sea surface temperature is 16.1°C (60.9°F).
Ten Warmest Years (1880–2021)
The following table lists the global combined land and ocean annually averaged temperature rank and anomaly for each of the 10 warmest years on record.
1 = Warmest
Period of Record: 1880–2021
|Year||Anomaly °C||Anomaly °F|
The following information was compiled from previous NCEI monitoring reports and public reports by National Hydrometeorological Services (NHMSs; peers of the U.S. National Weather Service).
The year was characterized by much-warmer-than-average 2021 temperatures across much of the globe, with record-high annual temperatures across parts of northern Africa, southern Asia, southern South America, as well as across parts of the Atlantic and Pacific Oceans. Meanwhile, cooler-than-average temperatures were limited to parts of the central and eastern tropical Pacific Ocean. However, no land or ocean areas had a record-low temperature for 2021.
North America had its seventh warmest year on record with a temperature that was 1.40°C (2.52°F) above average. Nine of North America's 10 warmest years have occurred since 2001, with the year 1998 among the 10 warmest years on record. The year 2021 also marks North America's 25th consecutive year with temperatures, at least nominally, above average. The yearly temperature for North America has increased at an average rate of 0.13°C (0.23°F) since 1910; however, the average rate of increase is a little more than twice as great (0.29°C / 0.52°F) since 1981.
The year began with much-above-average temperatures across much of northern North America, resulting in a near-record warm January. However, weather patterns quickly changed by the following month as a strong negative Arctic Oscillation was present during the first half of February, allowing cold Arctic air to reach to the mid-latitudes. Much of North America had temperatures that were at least 3.0°C (5.4°F) below average. Overall, the February 2021 temperature departure for North America was -1.34°C (-2.41°F) — North America's coldest February since 1994. The following months of March and June through October ranked among North America's top 10 warmest for each respective month. Of note, June 2021 was North America's warmest June on record with a temperature that was 2.0°C (3.6°F) above average, surpassing the previous record set in 2016 by 0.33°C (0.59°F). The months of September and October ranked as North America's third and second warmest, respectively.
- Please see the U.S. national annual report for information on the 2021 climate conditions across the U.S.
- Really cold Arctic air moved towards the mid-latitudes during the first half of February. According to the Government of Canada, the Prairies had maximum temperatures that were as high as -34.0°C (-29.2°F) and nighttime wind chills between -45°C to -55°C (-49°F to -67.0°F), setting many new record temperatures going back to 50 years. The extreme cold temperatures caused ruptures in water mains and cracked rail lines and set records for energy demand.
- During the last week of June, an extreme heat wave affected much of the northwestern contiguous U.S. and western Canada with maximum (daytime) temperatures surpassing 38.0°C (100°F), which is not typical for the region. Maximum temperatures were at least 16.0°C (28.8°F) above average across the region. According to the World Meteorological Organization, Lytton, British Columbia, Canada, set a new national maximum temperature record for three consecutive days. The latest record was 49.6°C (121.3°F) set on June 29, which is a maximum temperature more typical of summer temperatures in the Middle East. The intense heat was blamed for close to 800 reported deaths and hospitalizations related to the heat across Western Canada. In the U.S., preliminary reports stated that the heat affected crops such as berries and wheat.
- The Hawaiian region's yearly temperature was the coolest since 2012, despite it being above-average.
- The Caribbean region had its eighth warmest year on record. Nine of the region's 10 warmest years have occurred since 2005.
- Mexico set a new August maximum temperature record on August 3, 2021. The station in Mexicali, located in northwestern Mexico, recorded a maximum temperature of 50.4°C (122.7°F). This surpassed the previous record for the month that was set only last year (2020) when temperatures soared to 50.2°C (122.4°F) in Ejido Nuevo Leon (northwestern Mexico).
The year 2021 was South America's sixth warmest year on record at 1.09°C (1.96°F) above average. The year 2021 also marked South America's 45th consecutive year with temperatures, at least nominally, above average. Nine of South America's 10 warmest years have occurred since 2012. The year 1998 also ranks among South America's 10 warmest years on record. The yearly temperature for South America has increased at an average rate of 0.14°C (0.25°F) per decade since 1910; however, the average rate of increase is nearly double that value (0.23°C / 0.41°F) since 1981.
Much of South America had above-average monthly temperatures during the year. The months of April and August through December each had a monthly temperature that ranked among the top 10 warmest for their respective months. Of note, September was South America's warmest September on record with a temperature departure of +1.86°C (+3.35°F). Compared to all months, the South America September temperature departure was the second highest in the 1,344 monthly record and only 0.05°C (0.09°F) shy of tying the record high departure of 1.91°C (3.44°F) set on August 2015. The country of Argentina had its second warmest September since national records began in 1961. According to Argentina's Servicio Nacional Meteorológico, minimum temperatures were above average during the month, with several locations setting new minimum temperatures on record.
- Argentina's national temperature for 2021 ranked among the top six warmest years on record, with a national temperature departure of 0.5°C (0.9°F) above average. The year 2021 was the 11th consecutive year with a temperature above average.
The year 2021 was Europe's ninth warmest year on record at 1.28°C (2.30°F) above average. The year 2021 also marked the 25th consecutive year with temperatures, at least nominally, above average. Europe's 10 warmest years have all occurred since 2007. Europe's annual temperature has increased at an average rate of 0.15°C (0.27°F) per decade since 1910; however, it has tripled to 0.45°C (0.81°F) since 1981.
Following a record warm year (2020), 2021 was characterized by above-average monthly temperatures throughout the year. Although Europe's April 2021 temperature was above average, it was Europe's coldest month of the year and it was the coldest April since 2003. Similarly, May 2021 was Europe's coldest May since 2004. Several European countries had their coldest April or May in at least 10 years. However, by June 2021, much-above-average temperatures engulfed much of Europe, resulting in Europe's second warmest June on record. Only June 2019 was warmer. In July, much-above-average temperatures were present across much of eastern and northern Europe, giving way to the third warmest July on record. By the end of the year, monthly temperatures were still above average, but didn't rank among the 10 warmest for each respective month.
- Parts of western and central Europe experienced really cold temperatures during the first week of April, with several locations setting new low minimum temperatures. Of note, there were several locations across Slovenia that had their coldest April temperature in over 100 years. The weather station in Nova Vas, southern Slovenia, recorded a minimum temperature of -20.6°C (-5.1°F) — a new all-time national record for April, exceeding the previous record of -20.4°C (-4.7°F) set on April 9, 1956 at Pokljuka. Vegetation across these areas was damaged due to the really cold temperatures.
- During the second week of August, an intense heat wave impacted parts of southern Europe and northern Africa, with some locations observing maximum (daytime) temperatures of 45.0°C (113.0°F) or higher. According to preliminary reports, Sicily, Italy saw maximum temperatures rise to 48.8°C (119.8°F) on August 11, 2021, which would become, if verified, Europe's highest maximum temperature on record. This new value would surpass the current record of 48.0°C (118.4°F) that was set in two different cities in Greece on July 10, 1977. Also, of note was the temperature of 49.0°C (120.2°F) set in Tunis, the capital of Tunisia. Once verified, this would be Tunis' highest maximum temperature for the month of August, surpassing the previous record of 46.8°C (116.2°F) set in 1982.
- Austria, as a whole, had its coldest year since 2010, with a temperature that was 0.1°C (0.2°F) below the 1991–2020 average. However, it ranked among the 25 warmest years since Austria's records began in 1768.
With a yearly continental average temperature of 1.33°C (2.39°F) above average, Africa had its third warmest year (tying with 2019) in the 112-year record. Only the years of 2010 (second) and 2016 (warmest) were warmer. Africa's 10 warmest years have all occurred since 2005. This was also Africa's 45th consecutive year with temperatures, at least nominally, above average. Africa's annual temperature has increased at an average rate of 0.13°C (0.23°F) per decade since 1910; however, it has more than doubled to 0.29°C (0.52°F) since 1981.
Monthly temperatures were above average for Africa during 2021. The months of January and April through December ranked among the 10 warmest for their respective months. Of note, January, June, and November were each record warm.
Asia had its seventh warmest year on record, with a temperature departure of 1.60°C (2.88°F) above the 1910–2000 average. Asia's 10 warmest years have occurred since 2007. This was also the 34th consecutive year that Asia had above-average temperatures. Asia's trend during the 1910–2021 period was +0.17°C (+0.31°F) per decade; however, the 1981–2021 trend is twice the longer-term trend (+0.37°C / +0.67°F).
The year began with much of the northern half of Asia observing temperatures that were at least 3.0°C (5.4°F) below average, while the southern half had above-average January temperatures. The January 2021 temperature for Asia was above average at +0.32°C (+0.58°F), marking Asia's coldest January since 2012. The months of February and March were characterized similarly to January, where much of the northern half of Asia had below-average temperatures, while much of the southern half had above-average temperatures. By May and the summer months, much-warmer-than-average temperatures were present across much of the continent. The months of May, June, and August were each second warmest on record for their respective months, while July was Asia's warmest July on record.
- Hong Kong had its warmest year on record with a mean temperature that was 24.6°C (76.3°F).
- During the last two weeks of February, a warm spell affected East Asia with several locations experiencing new maximum temperature records. According to reports, Beijing, the capital of the Republic of China, had a maximum temperature of 20.8°C (69.4°F) on February 20, 2021, which was the highest maximum temperature recorded in February. However, that record only lasted one day since the record was yet again broken the following day when temperatures soared to 25.6°C (78.1°F). This was also the earliest a maximum temperature of 25.0°C (77.0°F) was set in Beijing. Climatologically, Beijing's average maximum temperature in February is 4.0°C (39.2°F). Korea also set a new national February temperature when the city of Pohang had a maximum temperature of 24.9°C (76.8°F). This was 0.4°C (0.7°F) higher than the previous record set in 2004.
Oceania had an above average temperature of +0.67°C (+1.21°C). Despite it being a warmer-than-average year, it was the coldest year since 2012. Oceania's 10 warmest years have occurred since 1998, while the five warmest year have all occurred since 2005. The year 2021 also marked the 37th consecutive year with temperatures above average across Oceania. The 1910–2021 trend for Oceania was +0.12°C (+0.22°F) per decade; however, the trend is close to twice that during the 1981–2021 period (+0.20°C / +0.36°F per decade).
Although the year began with an above-average temperature for Oceania, the months of January through April had a temperature that was the coldest for their respective month since at least 2015. However, the Southern Hemisphere winter months of July and August were the only months to rank among the four warmest for their respective month. November was Oceania's coldest month in 2021, with a temperature below average and Oceania's coldest November since 1999. However, the year ended on a warm note, with December ranking as the eighth warmest December on record.
As indicated by the Global Percent of Normal Precipitation and Precipitation Percentiles maps below and as is typical, many stations were wet for the year, while many stations were dry. Also, as discussed below, extreme precipitation and drought events occurred across the world.
Significantly below-average annual precipitation occurred across parts of the western contiguous U.S., southern South America, northern Africa, the Middle East, and across some Pacific Islands. Significantly above-average annual precipitation occurred across northern South America, eastern Europe, western and eastern Australian coast, as well as parts of southern Asia.
- See the U.S. National Annual Climate and U.S. Annual Drought reports for additional information on drought and notable precipitation extremes across the U.S. during 2021.
- Tropical cyclone Eloise made landfall in Mozambique near Beira as an equivalent Category 1 hurricane in the Saffir-Simpson scale on January 23. The storm affected the region with high winds and heavy rain that triggered severe floods in the region. According to Mozambique's National Institute of Meteorology, Beira received 250 mm of rain in 24 hours, which is close to the region's monthly average precipitation total for the month of January. Over 175,000 people were affected by Eloise and more than 8,000 homes were damaged or destroyed, according to UN's Reliefweb. Before making landfall in Mozambique, Eloise also affected Madagascar as a tropical storm with strong winds and copious rain.
- Cyclone Seroja formed in the eastern Indian Ocean basin early in the month and crossed the coast of Western Australia on April 11. Seroja brought copious rain and strong winds to the region. Several locations had their highest daily rainfall on record. Seroja also affected Indonesia, causing historic floods and landslides in parts of the region.
- In the contiguous U.S., drought affected much of the West, the High Plains, the South, and the Great Lakes region, as well as the Southeast. As of 28 December 2021, over 89% the western U.S. was entrenched in moderate to exceptional drought. According to the June 29 U.S. Drought Monitor, an unprecedented heat wave affected much of the northwestern contiguous U.S. and western Canada at the end of the month, helping deteriorate drought conditions by increasing evaporative demand, drying out soils and vegetation, as well as straining water resources. In fact, the Northern Rockies and Plains region had its driest June in the 127-year record. Across western Canada, the warm and dry conditions during the end of the month contributed to the development of numerous wildfires in the region. Of note, the village of Lytton, British Columbia, Canada, had a devastating wildfire that forced the evacuation of residents and almost 90% of Lytton had burned to the ground.
- The Atlantic hurricane basin had an above-average activity this year with 21 named storms — the third highest number of named storms on record. Of note, Tropical Storm Claudette, which made landfall in Louisiana, U.S., on June 19, brought torrential rains, floods, and spawned a few tornadoes in the southeastern region. Claudette contributed to the wetter-than-average conditions across the southeastern contiguous U.S., especially across Alabama and Mississippi, which had their second and fifth wettest June on record. Before becoming a tropical storm, the disturbance that later became Tropical Storm Claudette brought heavy rain to parts of eastern and southern Mexico, prompting mudslides and overflowing rivers. Parts of eastern Mexico had twice their June normal precipitation.
- Several locations across southern Europe had a drier-than-average July. The dry conditions combined with very warm temperatures helped with the development and spread of dangerous wildfires in the region by the end of the month. According to media reports, destructive wildfires affected parts of southern and southwestern Turkey, forcing residents to evacuate. Devastating wildfires also affected parts of northeastern Spain. For the month as a whole, Spain had below-average July precipitation, receiving only 57% of normal July precipitation. Meanwhile, parts of western Europe had torrential rains that caused deadly floods during July 13–15, with some locations receiving at least twice their normal monthly precipitation in only three days. According to preliminary reports, over 140 fatalities across western Germany and Belgium were attributed to the devastating floods. The high flood levels were also responsible for damaging homes in the affected regions.
- According to the World Meteorological Organization, Zhengzhou, in the Henan province, China, received 382 mm (15.0 inches) — a little over half of its average annual precipitation of 641 mm (25.2 inches) — in only six hours on July 20 and more than 640 mm during a short period of four days. The copious rain prompted dangerous floods and over 20 fatalities were attributed to the heavy rain.
- Drier-than-average conditions engulfed much of Argentina during the month. According to Argentina's Servicio Nacional Meteorológico, about 75% of the Paraná basin was in moderate to exception drought, which encompasses about 70 million ha. Also, about 75% of the Paraguay river basin was also suffering some type of drought as of August 3. Precipitation total for southern Argentina was 200 mm below the 1981–2010 average during the three-month period of May through July. Lack of snow across Patagonia was also reported, with some locations reporting their lowest values since 2000.
- Tropical Storm Fred formed in the Atlantic basin on August 9. Fred passed south of Puerto Rico; however, the storm's outer rain bands brought heavy rain to parts of the island, with some locations receiving over 5 inches. The rains helped improve drought on the island. By August 11, tropical storm Fred made landfall in Hispaniola. According to media reports, the copious rain prompted the overflow of rivers, displacing over 4,000 people from affected areas. Families were left without power and access to water. As soon as Fred made landfall in Hispaniola, it was downgraded to a tropical depression. Once in the Gulf of Mexico, Fred regained its strength and made landfall in Florida's Panhandle as a tropical storm, weakening once again to a tropical depression shortly after landfall. However, Fred's remnants caused torrential downpours across the southeastern contiguous U.S. Parts of western North Carolina had over 12 inches (305 mm) of rain.
- Hurricane Grace made landfall twice over Mexico. The first time it was a Category 1 hurricane and made landfall in the Yucatan Peninsula on August 18. As soon as it made landfall, it weakened to tropical storm. Once it was back in the warm waters of the Bay of Campeche, it rapidly intensified to Category 3 — becoming a major a hurricane with sustained windspeeds of 125 mph (205 km h1). Grace became one of the strongest hurricanes to make landfall in eastern Mexico. The storm caused widespread damages in Mexico, causing floods and landslides, uprooted trees, brought power lines down, and damaged homes and schools.
- Hurricane Ida was a dangerous Category 4 hurricane when it made U.S. landfall in Louisiana on August 29, 2021 — the same day that Hurricane Katrina did 16 years before. Before impacting portions of the southern and northeastern U.S., Ida also caused significant damage to parts of Cuba, by destroying homes and bringing down power lines.
- Typhoon Conson was an equivalent Category 1 hurricane in the Saffir-Simpson scale at its strongest intensity. Conson made landfall across central Philippines on September 6, bringing strong winds and heavy rain that prompted floods in low-lying communities. A few days later, Typhoon Chanthu, an equivalent Category 5 hurricane in the Saffir-Simpson scale, made landfall on the Batanes Islands, northern Philippines, on September 11. Chanthu was responsible for destroying infrastructures across the Batanes Islands, as well as toppling poles and trees, causing power outages. Chanthu also affected Taiwan, with torrential rains and strong storm surges of up to 7 m (23 feet).
- In the North Indian Basin, Cyclone Gulab made landfall in southeastern India on September 26. Gulab brought torrential rains to parts of India, causing significant damages, such as toppling power lines, flooding roads, and damaging homes. By September 28, Gulab weakened significantly over land. However, once it reemerged in the Arabian Sea, the system strengthened once again, reaching an equivalent Category 1 hurricane intensity. Gulab made landfall on Oman on October 3, prompting dangerous floods.
- Drought conditions have severely impacted central and southern Brazil this year, resulting in one of the worst droughts for the nation in centuries. According to reports, the lack of rain has resulted in water scarcity, increased fire activity, and crop losses. The rainfall deficit also impacted the energy sector since hydroelectric reservoirs are low or empty, prompting the Brazilian government to encourage its residents to consume less energy. On September 27, strong winds caused a dust storm over San Pablo, reducing visibility drastically.
- Hong Kong had very wet conditions during October 2021, receiving over six times the monthly normal of 100.9 mm (4.0 inches). The heavy rain can be attributed to the tropical cyclones Lionrock and Kompasu. Overall, this was Hong Kong's second wettest October on record.
- In early October, copious amounts of rain fell across northern Italy, causing floods and landslides. It was reported that Liguria (northwestern Italy) had received 181 mm (7.1 inches) in one hour and over 900 mm (35.4 inches) in a 24-hour period. A medicane, which is similar to a tropical cyclone located in the Mediterranean, brought torrential rain to parts of Algeria, Tunisia, and southern Italy at the end of the month. The heavy rain prompted severe floods and damaged over 100 homes.
- In British Columbia, Canada, record rainfall amounts fell in mid-November, causing dangerous floods and landslides. According to Environment Canada, a total of 100.4 mm (3.9 inches) fell on November 14 in Abbotsford, exceeding the previous record of 48.9 mm (1.9 inches) that was set in 1998. forced people to evacuate their homes and blocked roads. The copious rain also prompted rivers to overflow.
- Typhoon Rai was a strong and destructive typhoon that made landfall across southern Philippines on December 16. The typhoon brought strong winds and torrential rainfall and wreaked havoc across the region. According to preliminary reports, close to 400 people died and over 1,000 were injured due to the storm. After crossing the Philippines, Rai continued to move westward towards the South China Sea. Once Rai is on warm ocean water again, it re-itensified to an equivalent Category 5 storm, becoming the first super typhoon in the South China Sea in the month of December since 1961 (Source: Hong Kong Observatory).
Global Precipitation Climatology Project (GPCP)
The following analysis is based upon the Global Precipitation Climatology Project (GPCP) Interim Climate Data Record. It is provided courtesy of the GPCP Principal Investigator team at the University of Maryland.
The Global Precipitation Climatology Project (GPCP) monthly data set is a long-term (1979-present) analysis (Adler et al., 2018) using a combination of satellite and gauge information. An interim GPCP analysis completed within 10 days of the end of the month allows for use in climate monitoring and, in this case, an examination of the completed year (2021).
The estimated mean global precipitation for 2021 is estimated from the GPCP Monthly analyses as 2.66 mm d-1, just below (-.03 mm d-1) the 40-year climatological mean of 2.69. The mean values for ocean and land are 2.84 (-.06) and 2.28 (+.04) mm d-1, respectively. This kind of distribution is typical of La Niña and the year 2021 was dominated by La Niña SST conditions in the central Pacific (mean Niño 3.4 Index of -0.7C). La Niña produces a global mean below the climatological value and an overall negative (positive) ocean (land) anomaly number as the tropical rainfall shifts slightly toward the land areas in the tropics.
The mean precipitation map for 2021 (Fig. 3-top panel) shows the usual maxima of the tropics and mid-latitudes and dry zones in the sub-tropics and generally looks very similar to the long-term climatology (not shown). However, there are significant anomalies for 2021 from the long-term (1979–2020) as seen in the middle panel of Fig. 3. Along the Equatorial zone an intense positive anomaly covers most of the Maritime Continent and surrounding waters and a very strong negative anomaly feature with values beyond -3 mm d-1. Further east positive anomalies dominate the norther part of South America and the Atlantic ITCZ. These features are typical of La Niña conditions in general. This is confirmed by the La Niña composite (Fig. 3, bottom panel) constructed by taking the mean of annual precipitation anomaly fields for the years where the annual mean Niño 3.4 region SST index is in the one-third lowest (coolest) part of the range of SST values.
There is a striking correlation between anomaly features for 2021 and those in the composite (which does not include 2021), which are smoother (multiple years) and somewhat smaller in magnitude. This is true across the tropical Pacific, where the patterns are very alike and even extending into the mid-latitude parts of that ocean in both hemispheres. Stretching southeastward from the anomaly couplet in the tropical western Pacific, features extend to 60°S with the dry zone reaching the southern tip of South America, with the positive anomaly reaching the Straits of Magellan. With these features showing up in this year's and the composite anomaly fields indicates the long-distance influence of central Pacific ocean conditions. The Indian Ocean also reflects the La Niña effect with positive anomalies in the east and dry conditions in the west, extending into eastern Africa, but with positive anomalies over South Africa.
These tropical La Niña features in 2021 helped to fuel frequent flood conditions, for example, in Indonesia and Malaysia and surrounding countries and northern South America and eastern Brazil. The dry anomalies were associated with continuing dry and drought conditions over much of the southern half of South America and eastern Africa, even though South Sudan had serious floods and a weak 2021 and La Niña composite positive feature.
Over North America and surrounding oceans on both sides present a more complicated pattern, at least compared to the La Niña composite. The La Niña composite has a dry feature over the eastern Pacific extending across all the southern states with positive anomaly across Canada; however, the pattern for 2021 has a corresponding feature in the eastern Pacific, but over the continent things are very different. Although dry conditions are evident in south/central states, elsewhere things are very variable with some relief from the long-term drought in parts of the west coast. Opposite to the composite dry conditions dominate over Canada in 2021. The 2021 pattern across the tropical Atlantic also is not typical of La Niña, which is usually is associated with increased hurricane activity remained relatively dry.
As seen in the composite, La Niña usually means additional rainfall to Australia, but the anomaly map for 2021 there shows a mixed pattern with general dry conditions in the outback, but expected abundant rainfall in the southeast and along the northern coast.
La Niña conditions and Niño 3.4 Index values were not constant during the year. Figure 4 shows the anomaly maps for three-month periods during 2021. The Niño 3.4 Index varied during the year going from relative strong La Niña conditions early in the year to moderate conditions in the middle months (Index ~ -0.5) and back to a stronger La Niña situation (Index ~ -1.0) over last months of the year. This variation during the year is reflected in the seasonal anomalies in the tropics (Fig. 4) showing stronger La Niña-type patterns in the early and late months and weaker, but still discernible, such patterns in mid-year. Over Africa and South America the typical La Niña patterns vary during the year but are generally consistent during the year. Australia has varied patterns during the year. North America shows precipitation deficits dominating the southwest and west in the first half of the year, with varying surpluses to the east. Across Canada there is fairly consistent dryness, except in the last quarter of the year.
Although the GPCP global total precipitation is nearly constant and has no significant trend over the 40+ years of analysis, and mainly small variations, mainly related to ENSO effects, there are very significant regional trends (not including 2021), as seen in the top panel of Fig. 5. The trend pattern shows strong increases along the Pacific ITCZ, in the tropical Atlantic and Indian Ocean, with decreases over the sub-tropical oceans. This correspondence generally fits with the "wet getting wetter, dry getting drier" scenario. Features of the same sign as in the trend map are noted generally in the features in the 2021 anomalies (repeated in bottom panel of Fig. 5), indicating a 2021 reinforcement of the 40-year trend. Over the latitude band from 50°N-50°S the area-weighted correlation between the trend field and the 2021 anomaly field is +0.32, the positive correlation indicating that general reinforcement in 2021 of the longer-term changes occurring in the global precipitation pattern. Over North America this relationship is only weakly evident for 2021, despite the general La Niña conditions.
Ocean Heat Content
Ocean Heat Content (OHC) is essential for understanding and modeling global climate since > 90% of excess heat in the Earth's system is absorbed by the ocean. Further, expansion due to increased ocean heat contributes to sea level rise. Change in OHC is calculated from the difference of observed temperature profiles from the long-term mean.
|Basin||0-700 meters | Rank (1955-2021)|
|Entire Basin||Northern Hemisphere||Southern Hemisphere|
|Source: Basin time series of heat content|
The annual global ocean heat content (OHC) for 2021 for the upper 2000 meters was record high in 2021, exceeding the previous record set in 2020. The seven highest OHC have all occurred in the last seven years (2015–2021). During 2021, the heating was distributed throughout the world's oceans, with record-high heat across the North Atlantic Ocean, the North Pacific Ocean, and Mediterranean Sea.
The ocean heating is irrefutable and a key measure of the Earth's energy imbalance: the excess greenhouse gases in the air trap more heat inside the climate system and drives global warming. More than 90% of the heat accumulates in the ocean because of its large heat capacity, and the other heating is manifested in warming the atmosphere, warming and drying land, and melting land and sea ice. There are no reasonable alternatives aside from the human emissions of heat-trapping gases (IPCC 2001, 2007, 2013, 2020; USGCRP 2017).
For additional information on the 2021 OHC, please see the paper titled Another Record: Ocean Warming Continues through 2021 despite La Niña Conditions.
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