Wei et al. (1) report that the Tibetan Plateau is a net CO_2 sink that is 4 times greater than previously estimated. Model simulations in the same study suggest that the CO_2 sink will increase further as the climate becomes warmer and wetter in the future. These results have significant implications for understanding the responses of the carbon cycle to climate warming. However, Piao et al. (2) used different methods to estimate the size of China's terrestrial ecosystem carbon sink and proposed that it ranges from 170 Tg Cy~-1 to 350 Tg Cy~-1. This result from Piao et al. (2) shows that the estimated extent of the Tibetan Plateau carbon sink in Wei et al. (1) is an overestimate. Using net ecosystem production (NEP) to estimate the size of CO_2 sinks may neglect the effects of several key processes, for example, aquatic carbon export (3) and multiple anthropogenic activities (4). In addition, uncertainties associated with eddy covariance (EC) data processing may also lead to the overestimation of the carbon sink.
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