Oceanic measurements of carbon dioxide continue to decrease, as reported in this year's ocean carbon data atlas

SOCAT annual update for 2024 released

The release of this year’s Surface Ocean CO₂ Atlas (SOCATv2024) on June 19th revealed that the number of oceanic measurements of the climate change-driving greenhouse gas, carbon dioxide (CO₂), has continued to decrease, following a downward trend since 2018. The number of observations submitted to this annual update is as low as the more limited observing efforts from a decade ago, as seen in the graph below. The lack of data is especially evident in the subtropical and tropical regions of the Northern Hemisphere (south of 20°N latitude) and across the entire Southern Hemisphere.

SOCAT-fCO2-chart-by-year — The number of highly accurate (<5 µatm) surface ocean fCO₂ (fugacity of CO₂) values each year. Colors represent which version of SOCAT each measurement was released with.

The large geographical gaps in ocean carbon observations reduces the accuracy of climate assessments that use SOCAT data, such as the Global Carbon Budget. The annual release of the SOCAT data product is crucial to quantifying ocean CO₂ uptake – a critical ecosystem service that naturally removes ~25% of anthropogenic CO₂ from the atmosphere, offsetting the impacts of climate change caused by human-produced greenhouse gases. This absorption of CO₂ by the ocean means that relatively less carbon ends up in the atmosphere, reducing the greenhouse gas “blanket” that surrounds and warms the planet. While this ability of the ocean to act like a carbon-absorbing sponge is critical, it still has negative consequences, like ocean acidification, which can impact marine life and the people who depend on it.

“Without SOCAT, quantifying how much CO₂ the ocean uptakes would not be possible. It has been instrumental in developing tools to assess that uptake for the scientific community around the world who are invested in ocean carbon and climate science.”
– Dr. Denis Pierrot, NOAA oceanographer and member of the SOCAT global group

For instance, these estimates are important to global stakeholders, including WMO’s Global Greenhouse Gas Watch and the UNFCCC Global Stocktake, who use these estimates to calculate the Global Carbon Budget and to assess progress towards achieving the long-term goals of the Paris Climate Agreement. SOCAT is also endorsed by the UNESCO-IOC/SCOR International Ocean Carbon Coordination Project, the Surface Ocean Lower Atmosphere Study, the Integrated Marine Biogeochemistry and Ecosystem Research, and the Global Ocean Obs e rving System (GOOS).

Image of global map with ocean carbon data — *Surface ocean CO₂ from ships, drifters and autonomous surface platforms and moorings for all data in SOCAT version 2024.*

An international effort to collect data

SOCAT is an open access community-led international synthesis of surface ocean CO₂ measurements collected from ships, moorings, and autonomous surface vehicles (ASVs) across the global ocean. Over 100 members of the international ocean carbon community contribute data to SOCAT, including NOAA Global Ocean Monitoring and Observing Program (GOMO) supported scientists.

fCO2_measurements_2022-2023 — The number of fCO₂ surface ocean measurements (year months with 1° x 1° gridded) collected in 2022 and 2023 that were included in SOCATv2024.

One of the major networks of instruments collecting ocean carbon measurements for SOCAT is collectively known as the Surface Ocean CO₂ Reference Observing Network (SOCONET). A large portion of SOCONET utilizes ships of opportunity, where CO₂ sensors are installed on commercial ships to passively collect measurements as they transit the ocean from one port to the next. This opportunistic sampling allows collection of data not only from more locations across the surface ocean, but also more frequently as these ships usually repeat their routes. This is in contrast to research vessels that are commissioned specifically to sail once (or infrequently) along a specific route at a particular time. Additionally, SOCONET was recently formally recognized as a GOOS emerging network in acknowledgement of the importance of SOCONET to national and international climate studies and mitigation goals.

Unfortunately, there have been challenges to sustain funding of data processing for this international project which relies on voluntary efforts of a relatively small international team of scientists and industry collaborators. The ripple effects of fewer commercial ships operating during the COVID-19 pandemic combined with funding shortfalls resulted in a declining number of samples and, consequently, reduced data coverage.

Furthermore, the global south has always been relatively undersampled due to fewer commercial shipping demands, as seen in the map above. An estimated 90% of the human population lives in the Northern Hemisphere, reflecting a greater shipping demand, higher seagoing traffic, and thus more sample collection. Filling these Southern Hemisphere data gaps will require innovative solutions, such as an augmented fleet of ASVs like Saildrones and gliders.

NOAA is making strides towards filling observational gaps

The Biden-Harris Administration recently invested $2.1M from the Bipartisan Infrastructure Law (BIL) to expand SOCONET by installing a new generation CO₂ sensors on the NOAA Ship Ronald H. Brown and several U.S. academic research vessels (UNOLS), including the US Coast Guard Cutter Healy, deployed in climate-critical regions such as the Arctic and Southern Oceans. Carbon dioxide sensors will also be installed on Saildrone ASVs deployed during the Atlantic hurricane season to better constrain CO₂ flux during extreme conditions. These funds will also be used to support and improve future SOCAT products.

saildrone — An autonomous Saildrone glides across the ocean measuring oceanic carbon dioxide. Photo credit: Saildrone.

NOAA makes significant contributions to SOCAT

This latest release of SOCAT (version 2024) on June 19th contains 38.6 million, quality-controlled, in situ surface ocean fCO₂ (fugacity of CO₂) measurements collected between 1957 and 2023 with an estimated accuracy of better than 5 μatm. The GOMO-supported contribution to this effort is currently the largest coordinated program providing surface water CO₂ data to SOCAT from ships of opportunity and ASVs. NOAA also provides critical support of data management activities and community engagement. GOMO-funded scientists contributing to SOCAT include: Kevin O’Brien and Linus Kamb (NOAA PMEL & University of Washington), Simone Alin (NOAA PMEL), Nick Bates (Bermuda Institute of Ocean Science & Arizona State University), Alex Kozyr (NOAA NCEI & University of Maryland), Denis Pierrot (NOAA AOML), Adrienne Sutton (NOAA PMEL), Rik Wanninkhof (NOAA AOML), Colm Sweeney (NOAA GML), Leticia Barbero (NOAA AOML), David Munro (NOAA GML & University of Colorado Boulder), Brendan Carter (NOAA PMEL) and Richard Feely (NOAA PMEL). NOAA labs, Cooperative Institutes, and universities have been critical in carrying out this work, including the NOAA Pacific Marine Environmental La b & Cooperative Institute for Climate, Ocean, and Ecosystem Studies; the NOAA Atlantic Oceanographic and Meteorological Lab & Cooperative Institute for Marine and Atmospheric Studies; the Global Monitoring Laboratory & Cooperative Institute for Research in Environmental Sciences; and the Bermuda Institute of Ocean Sciences (BIOS) and Arizona State University. This program is managed by GOMO program managers Kathy Tedesco and Alyse Larkin, with support from Knauss Fellow Kyla Kelly.