Terrestrial ecosystems are offsetting a marine decline. Thus, indicating key implications for climate and planetary health

A recent study published on August 1 in Nature Climate Change indicates that global photosynthesis rose from 2003 to 2021, chiefly attributed to enhanced carbon absorption by terrestrial vegetation. This increase is largely counterbalanced by a concurrent reduction in photosynthetic activity among marine phytoplankton, especially in tropical and subtropical waters.

The research conducted by scholars at Duke University’s Nicholas School of the Environment underscores an increasing disparity between terrestrial and marine ecosystems, providing essential insights for climate prediction, carbon reduction, and ecological stewardship.

Why Photosynthesis Matters

Photosynthesis is the mechanism by which primary producers, including plants and algae, transform carbon dioxide into organic substances utilising sunlight. This mechanism constitutes the basis of almost all life on Earth. The key metric in this study, net primary production (NPP), represents the net amount of carbon fixed by plants and algae after accounting for their own respiration.

“Net primary production determines ecosystem health, supports food webs, and plays a vital role in carbon cycling and climate stability,” said lead author Yulong Zhang, research scientist in the lab of Wenhong Li at Duke University.

A First-of-Its-Kind Global Perspective

This study offers a comprehensive overview of both terrestrial and marine ecosystems, contrasting with prior research that examined them in isolation. The team utilised six satellite-derived datasets — three pertaining to terrestrial environments and three related to marine environments — covering the period from 2003 to 2021.

“For a comprehensive view of planetary health, we need to evaluate both terrestrial and marine photosynthesis together,” said co-author Nicolas Cassar, Bass Chair at the Nicholas School.

• Terrestrial NPP increased by approximately 0.2 billion metric tons of carbon per year, especially in temperate and high-latitude regions.
• Marine NPP decreased by about 0.1 billion metric tons per year, with declines concentrated in tropical and subtropical oceans, particularly in the Pacific.
• The net global increase in NPP was 0.1 billion metric tons per year.
  

This terrestrial increase was mostly ascribed to extended growing seasons in boreal regions and enhanced agricultural practices in temperate zones. Simultaneously, marine decreases were associated with increasing sea surface temperatures that diminish nutrient mixing, essential for phytoplankton viability.

Environmental Drivers Behind the Trend

The team assessed various environmental factors to explain the diverging trends:

• Land gains were associated with warmer temperatures in higher latitudes, increased precipitation, forest expansion, and agricultural intensification.
• Ocean declines were tied to warming sea surfaces, which create stratified water layers that limit nutrient availability for algae.
  

“The oceans showed stronger year-to-year variability in NPP, especially during El Niño and La Niña events,” said co-author Shineng Hu, assistant professor of climate dynamics.

Notably, La Niña events after 2015 were found to reverse some of the earlier declining trends in ocean productivity, highlighting the oceans’ sensitivity to climate variability.

Implications for Climate and Ecosystems

The study highlights the essential function of terrestrial ecosystems in mitigating reductions in global marine photosynthesis. Nevertheless, persistent declines in ocean net primary production, along with stagnation in tropical terrestrial zones, may undermine food webs, jeopardise biodiversity, and diminish the carbon sequestration potential of tropical areas.

“We don’t yet know how long terrestrial gains can offset marine losses,” Zhang said. “Sustained, integrated monitoring is essential for understanding the future of Earth’s biosphere.”

Key Points

• Photosynthesis around the world went risen from 2003 to 2021, thanks to plants on land.
• Photosynthesis in the ocean went down, especially in tropical and subtropical areas.
• The net gain in photosynthesis was 0.1 billion metric tonnes of carbon each year.
• Land became more productive because it got warmer, the growing seasons were longer, and the way people used the land changed.
• Warming waters and less mixing of nutrients were connected to ocean losses.
• Oceanic responses to climate events like El Niño were the main cause of yearly changes.
• To manage ecosystems and make climate plans, integrated monitoring is vital.

Original Publication
Authors: Yulong Zhang, Wenhong Li, Ge Sun, Jiafu Mao, Matthew Dannenberg, Jingfeng Xiao, Zuchuan Li, Haipeng Zhao, Qianru Zhang, Shineng Hu, Conghe Song and Nicolas Cassar.
Journal: Nature Climate Change
DOI: 10.1038/s41558-025-02375-1
Method of Research: Computational simulation/modeling
Article Title: Contrasting biological production trends over land and ocean
Article Publication Date: 1-Aug-2025