Anthropogenic climate change, driven by human activities, remains a pressing issue for our planet. The rapid changes in terrestrial carbon sinks and stores now challenge the effectiveness of existing climate mitigation strategies. To prevent catastrophic global warming, behaviors must change swiftly.

Gross primary productivity (GPP) offers critical insight into ecosystem health. It measures the carbon dioxide fixed by plants per unit of time and area.

Researchers recently analyzed the drivers of change in GPP to predict future trends and align global efforts with the Paris Agreement’s goal of limiting temperature increases to 2℃ (3.6℉). Their findings, published in Ecosystem Health and Sustainability, reveal troubling trends.

Carbon sinks are natural systems that absorb more carbon dioxide (CO2) than they release, playing a crucial role in regulating the Earth’s climate. While forests, oceans, and soil are well-known carbon sinks, other systems like wetlands, permafrost, and certain rocks also contribute significantly.

Wetlands, such as marshes and mangroves, store large amounts of carbon in their waterlogged soils. This slows decomposition, allowing carbon to remain trapped for centuries.

Permafrost, the frozen ground in Arctic regions, locks away organic material under ice. However, as temperatures rise, melting permafrost could release stored carbon, intensifying global warming.

Microscopic algae absorb CO2 in the ocean. When they die and sink to the seabed, the carbon is sequestered for long periods of time. Even geological formations, like basalt and limestone, can store CO2 through chemical reactions over thousands of years.

Human activities like deforestation and pollution reduce the effectiveness of these natural carbon sinks. However, their preservation is essential for climate stability.

Using long-term datasets spanning 1982–2016, the researchers observed a GPP decline across 68% of Earth’s terrestrial surface.

This indicates that many natural carbon sinks, like forests and soil, are reaching saturation. Once saturated, their efficiency to store carbon plummets. This saturation not only accelerates atmospheric warming but also diminishes plant productivity.

The study compared GPP trends over two distinct periods: 1982–1999 and 2000–2016. The researchers then quantified environmental contributions using the optimal-fingerprint approach, a linear regression model.

The analysis revealed a sharp GPP decline of over 50% between the two periods.

The experts identified a reduction in the CO2 fertilization effect as the main driver of declining global GPP. This effect refers to increased plant growth with higher atmospheric CO2 levels. However, rising CO2 no longer boosts plant productivity as expected.

“The decline in the CO2 fertilization effect is suggested to be the main driver accounting for the slowing-down of global GPP trends,” said Songhan Wang, researcher at Nanjing Agricultural University.

“Although it still has positive effects, the impact of rising CO2 on GPP on a global scale fell by about one-half from 2000 onwards compared to its impact in 1982–1999.”

The reduced impact of the CO2 fertilization effect may result from nutrient limitations in soil and leaves, highlighting another critical bottleneck in ecosystem productivity.

Land use and land cover change (LULCC) refers to alterations in the way land is used or its natural cover, such as converting forests into cities or farmland.

These changes, along with rising atmospheric CO2 levels, have significantly contributed to the decline in GPP.

Urbanization, which replaces vegetation with buildings and roads, reduces areas where plants can grow and absorb CO2. Deforestation, the clearing of forests for timber or land, destroys vital carbon sinks like trees and soil, releasing stored carbon into the atmosphere.

Similarly, agricultural expansion often involves replacing diverse ecosystems with monocultures, which are less efficient at absorbing CO2 and may degrade soil quality over time.

These activities not only reduce the ability of ecosystems to act as carbon sinks but also push them closer to collapse, limiting their capacity to mitigate climate change.

The findings highlight the inadequacy of relying solely on terrestrial carbon sinks for climate change mitigation.

Once carbon sinks saturate, they lose their ability to buffer against greenhouse gas emissions. Future strategies must focus on reducing anthropogenic emissions and achieving carbon neutrality to stay within safe climate thresholds.

Experts stress the importance of limiting global temperature increases to 2℃ to meet the Paris Agreement’s climate neutrality targets. This requires innovative, urgent, and collective efforts on a global scale.

This research involved contributions from leading scientists across institutions, including Nanjing Agricultural University, Spanish National Research Council (CSIC), Lund University, University of Arizona, and University of Exeter.

Their work was supported by numerous organizations, including the National Key R&D Program of China, NASA, and the Spanish Government.

The study provides a stark reminder of the urgent need for behavioral changes to combat climate change. The saturation of terrestrial carbon sinks marks a critical turning point in our planet’s fight against warming.

Without immediate action, the window to mitigate the worst effects of climate change may soon close.

The study is published in the journal Ecosystem Health and Sustainability.

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