Background: The Northwest China has experienced dramatic changes in agricultural land area in recent years; the effects of these changes on carbon storage are unknown and cannot guide further land development policies related to carbon emissions. In this study, we evaluated the effects of cropland changes (reclamation and transfer) during 1995-2015 on carbon storage in Northwest China by using land use data, carbon density data, and statistical yearbooks with the Intergovernmental Panel on

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... te Change (IPCC) method. Results: The results indicated that the area of cropland increased by 1.48×106 ha from 1995 to 2005, resulting in a total carbon sequestration of 12.46 Tg, in which conversion of cropland to forest (11.16 Tg) and other land to cropland (8.92 Tg) were the main sources of the increase in carbon storage. Specifically, regional carbon sequestration due to cropland changes exhibited an increasing trend during 1995-2002 (dominated by cropland transfer), a gradually decreasing trend during 2002-2009 (dominated by cropland reclamation), and stabilization since then (during 2009-2015). Conclusions: These results suggest that the development of high carbon density lands or the conversion of low carbon density lands are critical to increasing future carbon sequestration due to cropland change. We used a novel approach of combining land use data, carbon density data, and statistical yearbooks to assess the impact of cropland change on carbon storage; this method is promising in applications which guide agricultural land-use management.