# Decoupling the Impacts of Climate Change and Human Activities on Terrestrial Vegetation Carbon Sink
## 1 Introduction  
The terrestrial ecosystem plays an important function in mitigating climate warming and regulating the global carbon cycle [1]. Existing studies have reported that terrestrial ecosystems, on average, can offset approximately 30% of carbon dioxide emissions caused by anthropogenic activities each year [2]. Although terrestrial ecosystems as a whole serve as carbon sinks, there are still differences and uncertainties within their internal carbon sinks, which is primarily due to the heterogeneity of terrestrial ecosystems [3]. Moreover,the magnitude of the terrestrial carbon sink is greatly affected by various carbon cycle processes [4]. Theoretically, a terrestrial ecosystem can function as a carbon source, carbon sink, or exhibit a neutral carbon balance, and the carbon balance has been found to vary across ecosystem types [5]. Since the 1990s, numerous studies have been undertaken to assess terrestrial carbon sinks at different scales, utilizing ground surveys, flux measurements, atmospheric inversions, and model simulations [6]. Although current research has produced some findings on terrestrial carbon sinks using various methods, notable differences exist among different studies [7]. Furthermore, most of the existing research conducted a relatively insufficient analysis of the temporal variations and spatial differences [8]. With the development of remote sensing technology, terrestrial carbon cycling processes can usually be reflected by indicators like gross primary productivity (GPP) and net primary productivity (NPP), which significantly enhance the temporal and spatial analysis of terrestrial carbon sinks [9]. However, research on the terrestrial carbon cycle has increasingly focused on net ecosystem productivity (NEP), which can provide a more accurate measure of long-term carbon storage within ecosystems than plant biomass alone [10]. As a result, NEP serves as a stronger indicator of an ecosystem's potential to mitigate anthropogenic carbon emissions. Currently, the research on NEP mainly focuses on accurate accounting, spatial patterns, variation trends, driving mechanism, and future simulation [11; 12], in which the driving mechanism is one of the mainstream of NEP. Extensive studies indicate that climate change and human activities have significant positive or negative impacts on terrestrial vegetation productivity [13; 14]. [PERSON] et al. showed that stronger summer monsoons stimulate carbon uptake, and the warming hiatus lessens the decreasing trend of NEP [15]. [PERSON] et al. found that increasing precipitation has a positive impact on carbon sink [16]. [PERSON] et al. indicated that the capacity of China's terrestrial ecosystems to absorb carbon is being undermined by ongoing climate change [17]. [PERSON] et al. exhibited that the increase in atmospheric CO\({}_{2}\) concentration has a long-term impact on the carbon sink of China's terrestrial ecosystems. However, the enhancement of the terrestrial carbon sink due to the CO\({}_{2}\) fertilization effect will decline as the increase in atmospheric CO\({}_{2}\) levels slows down [18]. In addition, as an important anthropogenic driver, land use change has been shown to significantly affect vegetation productivity by altering the types and structures of ecosystems [19]. [PERSON] and [PERSON] found that approximately 50.8% of areas in China displayed a negative correlation between NEP and the expansion of built-up areas [20]. [PERSON] et al. revealed that the land use-driven nitrogen deposition in China reduced NEP by 0.4 Gg C yr\({}^{-1}\)[21]. The effects of climate change and human activities on terrestrial carbon sinks often vary across different regions and scales, exhibiting both positive and negative effects [22]. Therefore, disentangling the effects of climate change and human activities is vital for the management of terrestrial carbon sinks.