Soru

Passage:
In paleoclimatology, annual tree-ring width has long served as a primary proxy for reconstructing historical summer temperatures in subalpine environments. However, recent multi-proxy analyses demonstrate that ring-width growth in high-altitude bristlecone pines is frequently co-limited by spring soil moisture deficits and late-summer frost events, obscuring pure thermal signals. To isolate temperature trends, researchers turned to stable oxygen isotope ratios ($\delta^{18}\text{O}$) preserved within $\alpha$-cellulose from tree rings. Unlike ring width, which reflects cumulative metabolic biomass accumulation over an entire growing season, cellular $\delta^{18}\text{O}$ enrichment is driven principally by relative humidity and temperature during the brief two-to-three-week window of active cell-wall synthesis. Critics initially argued that isotopic fractionation during root water uptake would introduce confounding variability across different microclimates. Yet, empirical sampling across disparate soil depths revealed that root uptake of groundwater causes no isotopic fractionation; $\delta^{18}\text{O}$ shifts occur exclusively during foliar transpiration and subsequent carbohydrate synthesis. Consequently, anomalies in $\delta^{18}\text{O}$ series correlate with peak midsummer surface temperatures far more consistently than ring-width series do, particularly during decades characterized by unseasonal spring droughts.

Based on the premises provided in the passage, which of the following can be most logically inferred regarding paleoclimatic temperature proxies in high-altitude environments?