Terrestrial ecosystems are a key part of climate change mitigation strategies, as they absorb approximately one-third of anthropogenically emitted carbon. The capacity of terrestrial systems to continue to absorb anthropogenic CO2 and the extent of this absorption are an active research question that is important for mitigation plans and carbon budget estimates. Recent evidence However, they suggest limitations in the potential for terrestrial carbon sequestration and therefore mitigation potential. While models generally suggested a gradual decline in this sequestration over time with future climate change, 2023 brought an unexpected and dramatic collapse.

The year 2023 was marked by the surprising collapse of natural carbon sinks, which was reflected in a very high rate of CO2 growth. The terrestrial biosphere absorbed almost no net carbon that year, partly due to emissions from fires in Canada and drought in the Amazon. The impacts were not limited to land; the marine carbon sink in non-polar regions also declined in 2023, largely due to high surface temperatures, which in turn affected CO2 solubility. Overall, 2023 was an exceptional year, as El Niño conditions brought warmer temperatures and drier conditions to some parts of the world, negatively affecting biomass and facilitating increased emissions from forest fires.

It is worrying that The weakening of El Niño in 2024 did not bring the expected relief, which would allow the biosphere to recover. The global increase in hot and humid conditions in 2024 also led to large terrestrial carbon losses, and 2025 continues with persistent hot conditions. For example, June 2025 was the third warmest June on record globally, behind 2023 and 2024. These abrupt changes in the response of terrestrial carbon sinks are concerning, especially because the models could not predict themThis has serious implications for current mitigation strategies, which in many countries rely heavily on the land sector.

The effectiveness of restoration efforts aimed at reducing CO2 is compromised by high temperatures, fire risk, and drought. In addition, there is competition with agriculture and other land uses, which reduces the land available for reforestation efforts and their potential carbon impact. The impacts are already visible, for example, carbon sequestration in European forests has fallen more than expected, putting at risk the 2030 emissions reduction targets for the transition to net neutrality.

Carbon uptake by the terrestrial biosphere is by the balance of many different processes across ecosystems and scales that are difficult to fully account for in models. These processes include feedbacks that reduce the capacity for uptake, but also processes that could contribute to sustained uptake. In particular, the availability of nutrients such as nitrogen and phosphorus has been identified as a potential constraint on vegetation biomass that could strongly influence the future direction of terrestrial carbon uptake. However, plants have strategies to mitigate nutrient limitation that are currently not well integrated into models. Preliminary estimates suggest that better accounting for nutrient uptake could increase estimates of terrestrial carbon uptake.

In addition to natural feedback loops, Deforestation still the main contributor to the decline in terrestrial carbon absorption, despite recent initiatives such as the Glasgow Declaration and signs of declining deforestation rates in many countries. Deforestation, in addition to its impact on carbon sinks, also has consequences for local warming and heat-related mortality. Although forest regrowth offsets some of the emissions, limiting deforestation and protecting existing forests are critical, as deforestation and degradation undermine the resilience of remaining forest cover and carbon stocks.

These unexpected events in the natural world's ability to mitigate some of the impacts of climate change, demonstrated by the unprecedented failure of terrestrial carbon sequestration in 2023, highlight the importance of monitoring carbon dynamicsWe need long-term records like those from Mauna Loa, as well as satellite infrastructure and flux tower measurements. These data are urgently needed to monitor carbon cycle responses and benchmark mitigation efforts in an era when models are increasingly struggling to predict and simulate events and carbon impacts. JRi

The study was published in the journal Nature