As Arctic surface temperatures exhibit amplified warming, a warming center in the upper troposphere and lower stratosphere (UTLS) is also notable, which potentially plays a crucial role in polar-to-mid-latitude interactions. While the surface warming has accelerated recently, UTLS temperatures, however, have declined since 2001, as demonstrated by multiple reanalysis datasets. This shift in trends provides a unique opportunity to understand the factors influencing Arctic UTLS temperature changes. Further analysis indicates that the descending component of the Brewer-Dobson (BD) circulation over the Arctic was strengthened before 2000 but weakened thereafter. Simultaneously, Arctic lower stratospheric water vapor showed a decreasing trend before 2000, followed by an increasing trend. The weakening of the BD circulation led to reduced dynamical heating, and the increased water vapor resulted in enhanced radiative cooling, which together contributed to the cooling of the Arctic UTLS after 2000. Understanding these mechanistic drivers is crucial, as the decadal thermal variability of the Arctic UTLS may provide an important background for exploring the hemispheric redistribution of severe winter cold-air outbreaks. Ultimately, clarifying these UTLS temperature trends offers a foundational step to better understand potential polar-mid-latitude linkages beyond purely surface-driven explanations.