A research team led by Academician ZHU Jiaojun from the Institute of Applied Ecology, Chinese Academy of Sciences, has published a commentary in the Proceedings of the National Academy of Sciences (PNAS), responding to a recent article on carbon sink estimation in the Taklamakan Desert. The commentary provides a scientific assessment of claims that large-scale afforestation under China’s Three-North Protective Forest Program has transformed the hyper-arid region into a measurable terrestrial carbon sink, urging more rigorous interpretation of carbon accounting in hyper-arid desert ecosystems.

The discussion centers on a PNAS article published in January 2026 titled “Human-induced biospheric carbon sink: Impact from the Taklamakan Afforestation Project”, which attributed a measurable carbon sink to the afforestation in the Taklamakan Desert. In contrast, ZHU’s team drew on long-term field observations and established ecohydrological processes in arid environments to reassess the climatic constraints and carbon dynamics of such systems. ZHU Jiaojun and colleagues emphasized that the Taklamakan Desert, with annual precipitation below 80 millimeters and potential evaporation exceeding 2,500 millimeters, lacks the environmental conditions necessary for stable natural vegetation development.

ZHU’s team also questioned the seasonal framework used in the earlier study, which divided the year into “wet” and “dry” seasons. They noted that in hyper-arid inland deserts such as the Taklamakan, there is no true wet season, while the so-called dry season corresponds to winter, when average temperatures fall to around minus 5 degrees Celsius and plant physiological activity is effectively halted. Under these conditions, Zhu’s team argued, comparisons of vegetation carbon uptake across such seasonal categories are not physiologically meaningful.

Regarding atmospheric carbon dioxide variation, the commentary addressed the reported summer decline of approximately 3 parts per million (ppm) and its attribution to local afforestation. Zhu’s team pointed out that this magnitude falls within the background seasonal fluctuation range of 4 to 6 parts per million observed across the Northern Hemisphere due to large-scale vegetation phenology. They therefore stated that regional afforestation in the Taklamakan, where vegetation is mainly distributed along desert edges, cannot reasonably explain the observed background atmospheric signal.

From a hydrological perspective, ZHU Jiaojun and colleagues further highlighted the strong dependence of desert-edge vegetation on groundwater extraction and irrigation. They noted that groundwater levels in parts of the region are declining at an estimated rate of 8.6 millimeters per year, raising concerns about long-term water sustainability. Given the inherently low productivity and limited resilience of arid ecosystems, the team cautioned that climate variability and increasing drought stress could further weaken vegetation stability, with the possibility that areas currently acting as weak carbon sink may shift toward becoming carbon sources.

The commentary also clarified the functional positioning of afforestation within the Three-North Protective Forest Program. ZHU Jiaojun’s team stated that the primary objective of the program in the Taklamakan Desert is controlling desertification and limiting desert expansion rather than carbon sink. They stressed that carbon sink should be regarded as a secondary outcome limited by water resources and economic considerations. They further warned against extrapolating carbon sink estimates derived from desert-edge ecotones to the entire Taklamakan Desert, noting that such generalization could distort scientific understanding and policy expectations.