The climatic impact of volcanism depends critically on eruption style, magnitude, and composition, yet distinguishing these controls in deep-time records remains challenging. The Guadalupian-Lopingian (G-L) transition (similar to 260 Ma), which witnessed the demise of the Late Paleozoic Ice Age and concurrent eruptions of the Emeishan Large Igneous Province (ELIP) and the South China continental arc, provides an ideal natural laboratory for investigating volcanic-climate interactions. Here, we present an integrated multi-proxy study (including geochronology, geochemistry, mercury cycling proxies, and carbon isotopes) of the Yinpingshan section (South China), which recorded both volcanic sources. Our results document a transition in volcanic source from arc-dominated to LIP-dominated volcanism. Strong mercury anomalies from arc volcanism (Hg/TOC > 200 ppb/wt%) show minimal carbon isotope excursions, indicating limited climatic impact. In contrast, weaker ELIP-related mercury anomalies (Hg/TOC approximate to 80 ppb/wt%) coincide with significant negative delta C-13 excursions (up to -2 parts per thousand) and evidence of warming, implying massive CO2 emissions. Post-volcanic cooling is attributed to enhanced weathering and carbon burial. Our findings demonstrate that volcanic setting and scale, not merely the presence of volcanism, governed climatic impact, providing a new framework for understanding volcanic forcing during this critical transition.