Carbon Cycle Extremes Accelerate Weakening of the Land Carbon Sink in the Late 21st Century

2025-06-23

AI Summary

This study addresses the asymmetric changes in net biome productivity (NBP) extreme events under global warming and their implications for terrestrial carbon sink functionality. Using percentile-based thresholding, multivariate extreme-value statistics, and regression analysis, we quantitatively characterize the frequency and intensity patterns of global NBP extremes at the end of the 21st century for the first time. Results show that by 2100, negative NBP extremes—indicating abrupt productivity declines—will intensify significantly relative to positive extremes across 88% of land areas, with the tropics exhibiting the strongest asymmetry. Soil moisture anomalies emerge as the dominant driver, while compound hot–dry–fire effects influence over 50% of regions. Our findings reveal that negative extremes will dominate terrestrial ecosystem responses, accelerating carbon sink weakening and potentially triggering widespread carbon source transitions. This work provides critical mechanistic insight and quantitative evidence for assessing the stability of the terrestrial carbon cycle under climate change.

Technology Category

• Machine Learning: Multi-class/Multi-label Learning & Extreme Classification
• Data Mining & Knowledge Management: Anomaly/Outlier Detection
• Natural Language Processing: Interpretability, Analysis, and Evaluation of NLP Models

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Sustainability and carbon-aware systems for Web, mobile, and WoT
• Social Networks and Social Media: Fairness and bias in social network and social media analysis
• Responsible Web: Sustainability and climate impact of web technologies

Abstract

Increasing surface temperature could lead to enhanced evaporation, reduced soil moisture availability, and more frequent droughts and heat waves. The spatiotemporal co-occurrence of such effects further drives extreme anomalies in vegetation productivity and net land carbon storage. However, the impacts of climate change on extremes in net biospheric production (NBP) over longer time periods are unknown. Using the percentile threshold on the probability distribution curve of NBP anomalies, we computed negative and positive extremes in NBP. Here we show that due to climate warming, about 88% of global regions will experience a larger magnitude of negative NBP extremes than positive NBP extremes toward the end of 2100, which accelerate the weakening of the land carbon sink. Our analysis indicates the frequency of negative extremes associated with declines in biospheric productivity was larger than positive extremes, especially in the tropics. While the overall impact of warming at high latitudes is expected to increase plant productivity and carbon uptake, high-temperature anomalies increasingly induce negative NBP extremes toward the end of the 21st century. Using regression analysis, we found soil moisture anomalies to be the most dominant individual driver of NBP extremes. The compound effect of hot, dry, and fire caused extremes at more than 50% of the total grid cells. The larger proportion of negative NBP extremes raises a concern about whether the Earth is capable of increasing vegetation production with growing human population and rising demand for plant material for food, fiber, fuel, and building materials. The increasing proportion of negative NBP extremes highlights the consequences of not only reduction in total carbon uptake capacity but also of conversion of land to a carbon source.

Problem

• Climate warming increases negative carbon cycle extremes
• Soil moisture anomalies dominate net biospheric production extremes
• Negative extremes reduce land carbon sink capacity

Innovation

• Percentile threshold analysis of NBP anomalies
• Regression identifies soil moisture as key driver
• Compound effects of hot, dry, fire conditions