evidence: Enhanced Arctic sea ice melting controlled by larger heat discharge of mid-Holocene rivers [...] Arctic sea ice retreat is linked to extrapolar thermal energy import, while the potential impact of pan-Arctic river heat discharge on sea-ice loss has been unresolved. We reconstructed the Holocene history of Arctic sea ice and Russian pan-Arctic river heat discharge, combining ice-rafted debris records and sedimentation rates from the East Siberian Arctic Shelf with a compilation of published paleoclimate and observational data. In the mid-Holocene, the early summer (June–July) solar insolation was higher than that during the late Holocene, which led to a larger heat discharge of the Russian pan-Arctic rivers and contributed to more Arctic sea ice retreat. This intensified decline of early-summer sea ice accelerated the melting of sea ice throughout the summertime by lowering regional albedos. Our findings highlight the important impact of the larger heat discharge of pan-Arctic rivers, which can reinforce Arctic sea-ice loss in the summer in the context of global warming. [...] Arctic sea ice has dramatically declined under global warming, with feedback accelerating ongoing warming conditions1,2,3,4. However, future climate trends in association with sea ice melting remain elusive due to an insufficient understanding of the mechanism of retreat or even the absence of summer Arctic sea ice in the future. By referring to the Arctic climate of warmer intervals in the past, paleoclimate studies can provide clues for the future; e.g., the mid-Holocene (MH) was the most recent warmer climate interval relative to modern conditions.