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Greenhouse gas concentrations, global sea levels and ocean heat content reached record highs in 2021, according to the 32nd annual State of the Climate report, despite a double-dip La Niña event taking place in the Pacific Ocean.
Ocean climate change,
varies with La Niña, yet,
warming trends are clear.
PMEL researchers, Richard Feely, Greg Johnson and John Lyman, contributed to sections on ocean heat content, salinity, and the IPCC Sixth Assessment Report of the role of the oceans in the carbon cycle in the Global Oceans chapter. Greg Johnson continues to serve as an editor for the Global Oceans chapter along with Rick Lumpkin (NOAA AOML). Jim Overland and Muyin Wang contributed to the section on Arctic surface air temperature and the late Kevin Wood contributed the sea ice section.
The Global Oceans chapter discusses impacts of an unusual “double dip” La Niña in 2020 and 2021. The year 2021 started and ended with La Niña conditions - the cool phase of the El Niño-Southern Oscillation (ENSO) climate pattern. The Arctic chapter discusses the continued complex environmental changes in the Arctic. Air and ocean temperatures in the Arctic are intrinsically linked with sea ice and are directly connected to the biological productivity of the region. In the winters, drivers such as ENSO and the stratospheric polar vortex affect regional conditions and sub-seasonal variability. These processes add to the complexity of annually assessing the state of the Arctic, despite numerous examples of observed broadscale directional change across the region.
Notable findings from 2021 include:
Earth’s greenhouse gases were the highest on record. The major atmospheric greenhouse gas concentrations — carbon dioxide, methane and nitrous oxide — each rose once again to new record highs during 2021. The global annual average atmospheric carbon dioxide concentration was 414.7 parts per million (ppm). This was 2.3 ppm greater than 2020 amounts and was the highest measured in the modern observational records as well as the highest in at least the last million years based on paleoclimatic records.
Ocean heat and global sea level were the highest on record. The ocean sequesters the vast majority of the excess energy trapped in the Earth's system by greenhouse gases and other factors; estimated at more than 90% over the past half-century. Global ocean heat content, measured from the ocean’s surface to a depth of more than 6,000 feet, continued to increase and reached new record highs in 2021. For the 10th consecutive year, global average sea level rose to a new record high and was about 3.8 inches (97.0 mm) higher than the 1993 average — the year that marks the beginning of the satellite measurement record.
La Niña conditions lowered sea surface temperatures. La Niña conditions that began in mid-2020 continued for most of 2021. The annual global sea surface temperature in 2021 was lower than both 2019 and 2020 due in part to La Niña, but was still 0.52 of a degree F (0.29 of a degree C) higher than the 1991–2020 average. Approximately 57% of the ocean surface experienced at least one marine heatwave during 2021.
The Arctic was cooler overall, but some records were set. The Arctic had its coolest year since 2013, but 2021 was still the 13th warmest year in the 122 year record. Extreme heat events occurred during the summer. While the Arctic minimum sea ice extent was the 12th smallest extent in the 43 year record, the amount of multiyear ice — ice that survives one or more summer melt seasons — remaining in the Arctic was the second lowest on record. This indicates the Arctic’s sustained transition to a younger, thinner ice cover, which is more likely to experience complete melting in the future.
The 32nd international annual report of the world’s climate was published in the Bulletin of the American Meteorological Society (AMS) and includes contributions from more than 530 scientists in over 60 countries. It provides the most comprehensive update on Earth’s climate indicators, notable weather events and other data collected by environmental monitoring stations and instruments located on land, water, ice and in space.
The full report is available from Bulletin of the American Meteorological Society
Modified from NOAA press release published on August 31st, 2022 and Climate.gov story by NOAA National Centers for Environmental Information