In recent years, the Earth has undergone significant changes in its ecosystems. From 2003 to 2021, the planet has become greener, as photosynthesis levels have risen. However, this positive trend on land contrasts with troubling developments in the oceans, where marine ecosystems are struggling.
A Green Surge on Land
Between 2003 and 2021, global photosynthesis has seen an increase, primarily driven by the flourishing of land-based plants. According to a new study published in Nature Climate Change, terrestrial ecosystems have expanded their role in capturing carbon, thanks to warmer temperatures that have lengthened growing seasons. This surge in photosynthetic activity on land is particularly notable in higher latitudes, where plants have benefited from the extended growing seasons.
Yulong Zhang, a research scientist at Duke University, explained that photosynthesis is a crucial process that supports nearly all life on Earth. “As the foundation of food webs, net primary production determines ecosystem health, provides food and fibers for humans, mitigates anthropogenic carbon emissions, and helps to stabilize Earth’s climate,” he said.
The Ocean’s Struggles
In contrast to the surge in terrestrial photosynthesis, marine ecosystems have faced a decline in photosynthetic activity, particularly in tropical and subtropical regions. The study found a decrease of about 0.1 billion metric tons of carbon per year in marine primary production between 2003 and 2021. The most significant declines have occurred in the Pacific Ocean, where rising sea surface temperatures have hindered the growth of marine algae, essential producers in the ocean’s food chain.
Marine algae, also known as phytoplankton, are critical to carbon cycling in the oceans, yet they are struggling in warmer waters. The warming of the sea surface has caused cooler, nutrient-rich waters to become trapped beneath warmer layers, disrupting the necessary mixing of ocean currents that sustains algal life.
Credit: Yulong Zhang, et al, 2025
Climate Events and Ocean Sensitivity
One of the most striking findings in the study is the ocean’s heightened sensitivity to climate events such as El Niño and La Niña. While land ecosystems have shown a steady increase in photosynthetic activity, the oceans’ primary production fluctuates more dramatically from year to year. Strong climate events, particularly La Niña, have played a significant role in reversing trends in ocean primary production after 2015. These fluctuations suggest that marine ecosystems are far more vulnerable to rapid climate changes than their terrestrial counterparts.
“We observed that ocean primary production responds much more strongly to El Niño and La Niña than land primary production,” said Shineng Hu, an assistant professor of climate dynamics at Duke University. This sensitivity highlights the fragility of ocean ecosystems in the face of climate variability.
What This Means for Earth’s Future
The study also points out that while terrestrial ecosystems are compensating for some of the loss in marine primary production, these shifts could have long-term effects on global biodiversity. In tropical regions, where both land and ocean ecosystems are experiencing stagnation or decline, the foundation of food webs could be weakened. This disruption may eventually impact fisheries, local economies, and biodiversity, especially in tropical areas heavily dependent on marine life.
Furthermore, the decline in ocean primary production, particularly in the tropics, could reduce the ability of these regions to function as effective carbon sinks. As a result, Earth’s overall capacity to absorb carbon may be compromised, leading to intensified climate warming in the long run.