Global Land Carbon Sink Collapses, Shrinking Remaining Carbon Budget and Accelerating Warming Risk

For decades, the Earth's natural ecosystems have acted as a massive, silent buffer against human-caused climate change, absorbing roughly half of all carbon dioxide emissions pumped into the atmosphere. But in 2023, that vital planetary defense system temporarily broke down. Driven by record-breaking extreme heat, massive wildfires, and severe droughts, the world's forests, plants, and soils absorbed almost no carbon. The sudden collapse of the land carbon sink has alarmed scientists and raised urgent questions about the viability of global climate targets that rely heavily on nature to offset industrial emissions.[3][6]

A comprehensive analysis published in the National Science Review reveals the stark scale of the decline. In 2023, the global net land carbon sink plummeted to just 0.44 gigatonnes of carbon—its weakest performance since 2003 and roughly one-fifth of its average capacity over the past two decades. During the same period, the atmospheric growth rate of carbon dioxide measured at the Mauna Loa Observatory surged by 86 percent compared to the previous year. This spike hit a record high since observations began in 1958, despite global fossil fuel emissions increasing by only a fraction of a percent during that specific timeframe.[1][2]

The primary drivers of this terrestrial collapse were extreme weather events amplified by a warming climate and the onset of El Niño conditions. Researchers found that land regions exposed to extreme heat in 2023 contributed a gross carbon loss of 1.73 gigatonnes, indicating that record warming had a severe negative impact on ecosystem capacity. In the northern hemisphere, massive wildfires that ravaged Canada's boreal forests released an estimated 0.58 gigatonnes of carbon, effectively turning a traditional carbon sink into a massive source of emissions. Simultaneously, a severe drought in the Amazon basin caused an additional carbon loss of 0.31 gigatonnes, further crippling the biosphere's ability to draw down carbon.[1][2]

While the land sink faltered dramatically, the ocean—Earth's other major carbon buffer—also exhibited signs of long-term stress. Although the ocean sink slightly increased its carbon uptake in 2023 by 0.10 gigatonnes due to the transition from La Niña to El Niño in the equatorial Pacific, scientists warn that rising sea surface temperatures are steadily degrading its overall absorption capacity. Melting sea ice and shifting ocean currents threaten to disrupt the biological pump—the daily vertical migration of marine organisms that transports millions of tonnes of carbon from the surface to the ocean floor.[1][3]

The weakening of these natural sinks coincides with a continued, relentless rise in human emissions. According to the 2025 Global Carbon Budget, global carbon dioxide emissions from fossil fuels are projected to reach a record high of 38.1 billion tonnes this year. While the overall growth rate of emissions has slowed over the past decade—driven by the rapid deployment of renewable energy in major economies like China and India—the absolute volume of carbon being pumped into the atmosphere continues to climb, overwhelming the diminished capacity of natural ecosystems.[4][5]

This relentless accumulation of greenhouse gases, combined with the diminished capacity of natural sinks, has drastically shrunk the window for meaningful climate action. The Global Carbon Project estimates that the remaining carbon budget to limit global warming to 1.5 degrees Celsius above pre-industrial levels is now virtually exhausted. At current emission rates, the remaining budget of 170 billion tonnes of carbon dioxide will be entirely consumed in approximately four years, effectively closing the door on the most ambitious target of the Paris Agreement.[4][5]

The implications for international climate policy are profound and immediate. At least 118 nations currently rely on land-based carbon sinks—such as large-scale reforestation and soil management programs—to meet their national net-zero targets. The 2023 data demonstrates the extreme fragility of these ecosystems. If forests and soils can rapidly transition from carbon sinks to carbon sources during years of extreme heat and drought, relying on them to permanently offset ongoing fossil fuel emissions becomes a highly precarious, if not impossible, strategy.[3][6]

While researchers expect the land carbon sink to partially recover as the 2023–2024 El Niño pattern subsides, the underlying trend remains deeply concerning. The terrestrial biosphere in the northern hemisphere has shown a declining trend in carbon absorption since 2015, dropping by half over the last eight years. The unprecedented failure of the land sink in 2023 serves as a stark empirical warning: climate models may be underestimating the speed at which extreme events can erode nature's resilience, potentially accelerating global heating far beyond current projections.[1][3][6]