As if these developments weren’t already bad for climate science, the ocean carbon sink took a major blow. It sequestered approximately 10% less carbon (CO₂) in 2023 than what the experts expected. This decline is due to unprecedented high sea surface temperatures. The largest impacts are from the northern hemisphere’s extratropical latitudes and a strong El Niño event. Our ocean carbon sink has long been key to making climate change less bad by absorbing staggering amounts of CO₂. This year, it managed to sequester almost 1 billion tons of CO₂!
Now all those climatic variables are working together, leading to an unprecedented decline. This trend is highly concerning for the future effectiveness of the ocean as a climate mitigation tool and carbon sink. The ocean takes up around 90% of the additional heat from the greenhouse gases we’ve put into the atmosphere. This important role as nature’s climate change sponge continues to be increasingly threatened.
Factors Contributing to the Decline
The second explanation, the large drop in CO₂ absorbing power, can be mostly attributed to the increasing sea surface temperatures during all of 2023. The North Atlantic was a region of very strong warming directly affecting the ocean’s carbon uptake potential. Temperature anomaly spike was most severe in extratropical areas. Warm surface waters and other conditions combined to weaken the ocean’s capacity to absorb CO₂.
As we noted recently the North Atlantic has been unusually warm. At the same time, the tropical Pacific was experiencing very high temperatures due to the strong El Niño event this year. This phenomenon pushed warm surface water back toward the coast of South America, disrupting the balance of ocean currents and temperatures even more. That’s because El Niño is typically a big driver of the ocean’s natural carbon absorption. In 2023, it was so strong that it reversed currents, creating conditions that lowered CO₂ solubility and heightened outgassing.
The interplay between these extreme hot temperatures and other compensating forces were key to shaping how the ocean responded. Three overriding influences—temperature driven escape of CO₂, water column stratification and processes on the biological pump—dictated the carbon fate in 2023. The temperature-induced outgassing was especially intense in the North Atlantic, largely offsetting any CO₂ uptake that was happening in the tropics.
Implications for Future Carbon Absorption
The results for 2023 should strongly alarm everyone about the future ability of the ocean carbon sink to function at all. Researchers caution that if the worst trends persist, the ocean could absorb much less of our CO₂ in the years to come. This would have disastrous consequences for international climate change policy and wields unprecedented power to obstruct U.S. The ocean is the original carbon sink, taking up on average one-fourth of anthropogenic CO₂ emissions in the past several decades and moderating atmospheric CO₂ concentrations.
Without the ocean’s ability to act as a long term carbon sink we would be facing atmospheric CO₂ concentrations much greater than today’s. This would almost certainly lead to global temperatures surpassing redlines, including the well-known 1.5-degree warming threshold. Reduced absorption capacity is an even greater hurdle. We desperately need to do further research and think creatively about how to restore the world ocean’s health and its capacity to sequester carbon.
Now, researchers are sounding the alarm on protecting our marine ecosystems and studying how they react to climate change. Long-term resilience of the ocean carbon sink depends on strong conservation measures and bold global climate action.
Understanding Ocean Dynamics
The intricate interplay of factors influencing the ocean’s carbon absorption abilities highlights the importance of ongoing observation and analysis. The reduced dissolved inorganic carbon (DIC) levels in near-surface layers during 2023 indicate that both natural processes and anthropogenic factors are influencing ocean chemistry at unprecedented rates.
Climate analyses models predict that as global temperature continues to increase, ongoing changes in ocean stratification could result in even greater declines of CO₂ absorption. The biological pump is largely dependent on marine organisms to sequester carbon. It too is deeply impacted by these changes, forming a climate feedback loop that stands to exacerbate current climate issues.
New research to understand these complex dynamics tells a different story. A tug of war ocean. The outgassing of CO₂ increases with higher temperatures while reducing levels of dissolved CO₂. They can trigger compensatory processes that temporarily halt or even reverse increases in carbon uptake. As demonstrated this year in 2023, these stabilizing forces can be easily overwhelmed by larger warming trends.
