Global Land Carbon Sink Drops Sharply, Signaling Faster-Than-Expected Failure of Natural Climate Buffer

For decades, the Earth’s forests, grasslands, and wetlands have acted as a silent safety net, absorbing roughly one-third of the carbon dioxide humanity pumps into the atmosphere. This natural buffer, known as the terrestrial carbon sink, has historically kept global temperatures from rising even faster.[3]

But new data suggests this foundational climate defense is fraying much earlier than anticipated. Across a series of recent studies and preliminary atmospheric measurements, scientists have observed a sharp, unprecedented drop in the amount of carbon absorbed by land ecosystems in 2023 and 2024.[2]

The findings challenge a core assumption built into international climate models: that nature would continue to subsidize human emissions well past mid-century. Instead, researchers are warning that the land sink is transitioning from a reliable sponge to a highly volatile system.[3]

The first major warning sign arrived in 2023, the hottest year on record. Preliminary findings revealed that forests, plants, and soils absorbed almost no net carbon that year, driven by extreme heat and widespread drought.[3]

The trend accelerated in 2024. According to data published in the National Science Review, the atmospheric CO2 growth rate reached a record high of 3.73 parts per million last year.[2]

This spike occurred despite fossil fuel emissions increasing by less than 1 percent, pointing directly to a failure in natural absorption. Tropical lands, in particular, flipped from being a net sink to a net source of emissions.[2]

The breakdown is driven by two distinct mechanisms. During intense droughts and wildfires, such as those seen recently in Canada and the Amazon, trees burn or die, releasing decades of stored carbon back into the sky.[3]

However, the 2024 data revealed a different, more insidious threat: heat-driven respiration. Even in regions where increased rainfall made landscapes greener, higher temperatures caused soil microbes and plant tissues to respire at accelerated rates.

This biological exhaust outpaced the carbon drawn down through photosynthesis, releasing an estimated 2.6 billion extra tons of CO2—roughly equivalent to the annual emissions of India.

Beyond the recent spikes, new research suggests the land sink may have always been weaker than previously thought. A September 2025 study in Science Advances utilized remote sensing and machine learning to directly measure global vegetation biomass.[1]

The University of California, Irvine researchers concluded that over the past two decades, plants absorbed only about half the carbon reported in previous Intergovernmental Panel on Climate Change (IPCC) assessments.[1]

This weak land carbon sink hypothesis was corroborated by a separate October 2025 paper in Science Bulletin, which used AI tracking to confirm a halving of the global land sink's estimated capacity.[4]

Despite the alarming data, some climate scientists caution against declaring a permanent collapse. Analysts at Carbon Brief note that the extreme lows of 2023 and 2024 were heavily influenced by a strong El Niño cycle, and the sink is expected to partially recover in cooler, wetter years.

Furthermore, if the land sink has historically absorbed less carbon, the math of the global carbon budget must be rebalanced. Researchers suggest that oceans may be absorbing slightly more carbon than estimated, and historical fossil fuel emissions might have been slightly over-reported.[1]

Regardless of the exact baseline, the trajectory is clear: the land sink is weakening as global temperatures rise.

If ecosystems cease to remove their traditional 30 percent slice of human emissions, the remaining carbon budget for keeping global warming below 2°C is significantly thinner than official tallies suggest.

Governments and industries relying on land-based carbon offsets to reach net-zero targets may find those natural assets unable to deliver, forcing a requirement for much steeper, faster cuts to fossil fuel emissions at the source.[3]