The State of the Climate in 2021 report was released today by the American Meteorological Society, showing greenhouse gas concentrations, global sea levels, and ocean heat content reached record highs in 2021 despite a La Niña event taking place in the Pacific Ocean.
Compiled by NOAA’s National Centers for Environmental Information, State of the Climate in 2021 is based on contributions from over 500 scientists from around the world. It provides a detailed update on Earth’s climate indicators, extreme weather events, and other data collected by environmental monitoring stations and instruments located on land, water, ice, and in space.
Scientists, including a number of researchers at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), communicate the impacts of the Earth’s warming and changing environments in Chapter 3 of the report, “Global Oceans,” with sections including Meridional Overturning Circulation, Ocean Currents, and IPCC AR6 Assessment of the role of the oceans in the carbon cycle. AOML researchers also contributed to Chapter 4, “Tropics,” by authoring two sections of the chapter, Tropical Cyclones and Tropical Cyclone Heat Potential.
The Global Oceans chapter discusses impacts of an unusual “double dip” La Niña in 2020 and 2021. La Niña is characterized by unusually cold ocean temperatures in the eastern Equatorial Pacific that impact global weather patterns. La Niña conditions that began in mid-2020 continued into mid-2021, then warmed slightly for a couple of months before returning to cold La Niña conditions for the remainder of the year. La Niña tends to decrease annual surface temperatures on the global scale. However, despite the La Niña conditions in 2021 the global annual surface temperature this year was still the six highest on record.
Due to a combination of melting land ice and ocean warming, for the 10th-consecutive year, global mean sea level reached a new record high in 2021. During the period 1993-2002, the sea level increased at an average rate of 2.1 mm per year, while between 2013 and 2021 it increased at a rate of 4.4 mm per year due to loss of ice mass from glaciers and ice sheets. The ocean has stored about 91% of the energy gained by Earth’s climate system over the past half century, and global ocean heat content continues to increase, from the surface to depths greater than 4000 meters, reaching a new record high in 2021. Additionally, approximately 57% of the ocean surface experienced at least one marine heatwave in 2021, which is defined as sea surface temperatures in the warmest 10 percent of all recorded data for a particular location for at least five days.
The ocean absorbs around 23% of the anthropogenic carbon dioxide in the atmosphere leading to increased acidity (lower pH). Open ocean surface pH has declined globally over the last four decades and is now the lowest it has been for at least 26,000 years. As the pH of the ocean decreases, its capacity to absorb carbon dioxide from the atmosphere also declines.
The Tropics chapter focuses on the first negative Indian Dipole event since 2016. As previously mentioned, La Niña conditions were present in the central and eastern equatorial Pacific Ocean during most of 2021. In July, a negative Indian Ocean dipole event became established, with above-average temperatures in the east Indian Ocean and below-average temperatures in the west. La Niña impacts climate patterns around the globe, while the phase of Indian Ocean dipole primarily affects the weather of the surrounding continents in the Southern Hemisphere.
Additionally, the Tropics chapter documents the 97 named tropical cyclones observed during the Northern Hemisphere and Southern Hemisphere storm seasons. This number was well above the 1991–2020 average of 87 tropical cyclones due to favorable ocean and atmospheric conditions. The North Atlantic hurricane basin recorded 21 named storms, the third most active year recorded for the basin, behind the record years of 2020 when 30 cyclones occurred and 2005 when 28 cyclones occured.
Chapter 3 “Global Oceans” was co-edited by Rick Lumpkin, the Director of AOML’s Physical Oceanography Division, and Greg Johnson (NOAA’s Pacific Marine Environmental Laboratory). AOML authors are Francis Bringas, Shenfu Dong, Gustavo Goni, Rick Lumpkin, Renellys Perez, Claudia Schmid, Denis Volkov, and Rik Wanninkhof. Chapter 4 “Tropics” was edited by Howard Diamond (NOAA) and Carl Schreck (NC State), with AOML authors Stanley Goldenberg, Gustavo Goni, and Francis Bringas contributing to the chapter.
Research and synthesis by researchers from AOML and other institutions appearing in the 2021 State of the Climate report contributes to the body of research documenting our changing climate and can be used to inform further research, policy decisions, and management actions.