TY  - JOUR
AU  - Blunden, J.
AU  - Boyer, T.
TI  - State of the Climate in 2020
JO  - Bulletin of the American Meteorological Society
VL  - 102
IS  - 8
SN  - 1520-0477
CY  - Boston, Mass.
PB  - ASM
M1  - FZJ-2021-03342
SP  - S1 - S475
PY  - 2021
AB  - In 2020, the dominant greenhouse gases stored in Earth’s atmosphere continued to increase. The annual global average carbon dioxide (CO2) concentration at Earth’s surface was 412.5 ± 0.1 ppm, an increase of 2.5 ± 0.1 ppm over 2019, and the high-est in the modern instrumental record and in ice core records dating back 800,000 years. While anthropogenic CO2 emissions were estimated to decrease around 6%–7% globally during the year due to reduced human activities during the COVID-19 pan-demic, the reduction did not materially affect atmospheric CO2 accumulation as it is a relatively small change, less even than interannual variability driven by the terrestrial biosphere. The net global uptake of ~3.0 petagrams of anthropogenic carbon by oceans in 2020 was the highest in the 39-year record and almost 30% higher than the 1999–2019 average. Weak El Niño-like conditions in the eastern equatorial Pacific Ocean in early 2020 cooled and transitioned to a moderate La Niña later in the year. Even so, the annual global surface tem-perature across land and oceans was among the three highest in records dating to the mid- to late 1800s. In Europe, 17 countries reported record high annual mean temperatures, contributing to  the  warmest  year  on  record  for  the  European  continent.  Elsewhere, Japan, Mexico, and Seychelles also experienced re-cord high annual mean temperatures. In the Caribbean, Aruba, Martinique, and St. Lucia reported their all-time monthly maximum temperatures.  In  the  United  States,  Furnace  Creek  in  Death  Valley, California, reached 54.4°C on 16 August—the hottest temperature measured on Earth since 1931, pending confirma-tion. North of 60°N, the annual mean temperature over Arctic land areas was 2.1°C above the 1981–2010 average, the highest in the 121-year record. On 20 June, a temperature of 38°C was observed  at  Verkhoyansk,  Russia  (67.6°N),  provisionally  the  highest temperature ever measured within the Arctic Circle. Near the opposite pole, an atmospheric river—a long, nar-row region in the atmosphere that transports heat and moisture from sub-tropical and midlatitudes—brought extreme warmth from sub-tropical and midlatitudes to parts of Antarctica during austral summer. On 6 February, Esperanza Station recorded a temperature of 18.3°C, the highest temperature recorded on the  continent,  surpassing  the  previous  record  set  in  2015  by  1.1°C. The warmth also led to the largest late-summer surface melt event in the 43-year record, affecting more than 50% of the Antarctic Peninsula. In August, daily sea ice extent in the waters  surrounding  Antarctica  shifted  from  below  to  above  average, marking the end of persistent below-average sea ice extent since austral spring 2016.In  the  Arctic,  when  sea  ice  reached  its  annual  maximum  extent in March, thin, first-year ice comprised ~70% of the ice; the thickest ice, which is usually more than four years old, had declined by more than 86% since 1985 to make up just 2% of total ice in 2020. When the minimum sea ice extent was reached in  September,  it  was  the  second  smallest  except  for  2012  in  the 42-year satellite record. The Northern Sea Route along the Siberian coast was open for about 2.5 months, from late July through mid-October, compared to less than a month typically.Glaciers across the global cryosphere lost mass for the 33rd consecutive  year,  and  permafrost  temperatures  continued  to  reach  record  highs  at  many  high  latitude  and  mountain  locations. In the Northern Hemisphere, lakes froze three days later and thawed 5.5 days earlier on average. In Finland, the average duration of lake ice was 42 days shorter. Record high spring temperatures in central Siberia drove rapid snow melt that contributed to the lowest June snow cover extent across Eurasia in the 54-year record.As is typical, some areas around the world were notably dry in 2020 and some were notably wet. The Middle East experi-enced  an  extreme  drought  during  autumn,  with  most  places  reporting  no  precipitation  in  October.  In  South  America,  the  Bolivian lowlands suffered one of its most severe droughts on record  during  autumn.  Drought  also  spanned  the  Chaco  and  Pantanal in Bolivia, Paraguay, and southern Brazil. The Paraguay River  shrank  to  its  lowest  levels  in  half  a  century.  A  decadal  “mega drought” in south-central Chile continued through its 11th year, with extreme conditions in the most populated areas. Argentina reported its driest year since 1995. In North America, drought continued to prevail in the West. The lack of moisture in drought-stricken regions often pro-vide ideal conditions for fire. Total fire emissions in the western United States in 2020 were almost three times higher than the 2003–10 mean. The Arctic experienced its highest fire year in terms of carbon emitted into the atmosphere, surpassing the record set in 2019 by 34%, with most of the fires occurring in Arctic Asia. In the tropics, the Amazon saw its highest fire  activity since 2012, while fire activity in tropical Asia—including Indonesia—was  one  of  the  lowest  on  record,  related  to  wet  conditions as La Niña evolved during the fire season. The 2020 Southwest Asian Monsoon season (June–September) was the wettest since 1981, also coincident with the emergence of  La  Niña.  The  Meiyu  rainy  season,  which  usually  occurs  between July and August over the Yangtze and Huaihe River Valleys  of  China,  was  extended  by  two  months  in  2020.  The  May–October total rainfall averaged over the area was the most since the start of the record in 1961. Associated severe flooding affected about 45.5 million people.A widespread desert locust infestation during 2019–20 impacted equatorial and northern East Africa, as heavy rains and prevailing winds were favorable for breeding and movement of swarms across Kenya, Ethiopia, northeastern Somalia, Uganda, South Sudan, and northern Tanzania. The massive infestation destroyed  thousands  of  square  kilometers  of  cropland  and  pasture lands, resulting in one million people in need of food aid in Ethiopia alone. Extremely heavy rains in April also trig-gered widespread flooding and landslides in Ethiopia, Somalia, Rwanda, and Burundi. The Lake Victoria region was the wettest in its 40-year record. Across the global oceans, the average ocean heat content reached a record high in 2020 and the sea surface temperature was the third highest on record, surpassed only by 2016 and 2019. Approximately 84% of the ocean surface experienced at least one marine heatwave (MHW) in 2020. For the second time in the past decade, a major MHW developed in the northeast Pacific, covering an area roughly six times the size of Alaska in September. Global mean sea level was record high for the ninth consecutive  year,  reaching  91.3  mm  above  the  1993  average  when  satellite  measurements  began,  an  increase  of  3.5  mm  over 2019. Melting of the Greenland Ice Sheet accounted for about 0.8 mm of the sea level rise, with an overall loss of 293 ± 66 gigatons of ice.A total of 102 named tropical storms were observed during the  Northern  and  Southern  Hemisphere  storm  seasons,  well  above the 1981–2010 average of 85. In the North Atlantic, a record  30  tropical  cyclones  formed,  surpassing  the  previous  record  of  28  in  2005.  Major  Hurricanes  Eta  and  Iota  made  landfall along the eastern coast of Nicaragua in nearly the same location within a two-week period, impacting over seven million people across Central America. In the western North Pacific, Super Typhoon Goni was the strongest tropical cyclone to make landfall  in  the  historical  record  and  led  to  the  evacuation  of  almost 1 million people in the Philippines. Very Severe Cyclonic Storm Gati was the strongest recorded cyclone to make landfall over Somalia. Bosaso, in northeast Somalia, received 128 mm of  rainfall  in  a  24-hour  period,  exceeding  the  city’s  average  annual total of 100 mm.Above  Earth’s  surface,  the  annual  lower  troposphere  temperature  equaled  2016  as  the  highest  on  record,  while  stratospheric temperatures continued to decline. In 2020, the stratospheric winter polar vortices in both hemispheres were unusually  strong  and  stable.  Between  December  2019  and  March  2020,  the  Arctic  polar  vortex  was  the  strongest  since  the  beginning  of  the  satellite  era,  contributing  to  record  low  stratospheric ozone levels in the region that lasted into spring. The anomalously strong and persistent Antarctic polar vortex was linked to the longest-lived, and 12th-largest, ozone hole over the region, which lasted to the end of December.
LB  - PUB:(DE-HGF)16
DO  - DOI:10.1175/2021BAMSStateoftheClimate.1
UR  - https://juser.fz-juelich.de/record/894657
ER  -