Dating and geomorphology of shoreline features in the Qinghai Lake basin of northwestern China suggest that, contrary to previous interpretations, the lake likely did not reach levels 66–140 m above modern within the past ∼ 90,000 yr. Maximum highstands of ∼ 20–66 m above modern probably date to Marine Isotope Stage (MIS) 5. MIS 3 highstands are undated and uncertain but may have been at or below post-glacial highs. The lake probably reached ∼ 3202–3206 m (+ 8–12 m) during the early Holocene but stayed below ∼ 3202 m after ∼ 8.4 ka. This shoreline history implies significantly different hydrologic balances in the Qinghai Lake basin before ∼ 90 ka and after ∼ 45 ka, possibly the result of a more expansive Asian monsoon in MIS 5.

Geomorphic features inherited from the mid-Holocene glacio-hydro-isostatic sea-level highstand that affected the central Pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming. Shoreline morphology on multiple islets of Funafuti atoll in central Tuvalu reflects a relative mid-Holocene sea-level highstand 2.2–2.4 m above modern sea level. Typical islets are composed of unconsolidated post-mid-Holocene sediment resting disconformably on cemented coral rubble formed beneath now-emergent mid-Holocene reef flats. Exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack. Islets lacking cemented mid-Holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines. Any future sea-level rise ≥0.75 m, bringing high tide above the elevation of mid-Holocene low tide, might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid-Holocene reef platforms. As analogous threshold relations are inferred for other central Pacific atolls, the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea-level rise with respect to gross islet elevations.