Mass Loss From Thwaites Glacier Continues Even Without Ocean Melting

Pine Island and Thwaites glaciers dominate Antarctica's sea-level contribution. However, it remains unclear whether their ice loss is driven by anomalously warm present-day ocean conditions, perhaps linked to anthropogenic climate change, or are an ongoing response to historical natural climate anomalies. Here, we probe these drivers by subjecting three state-of-the-art ice-sheet models to an extreme hypothetical scenario of zero ocean melting. Pine Island responds by thickening and re-advancing to the prominent seabed ridge on which it was grounded prior to 1940. In contrast, Thwaites continues to lose ice (at a decreasing rate) for 150 years, despite the absence of ocean melting. Since all present-day ocean forcing via melt is removed, this demonstrates that the ongoing Thwaites ice loss is at least partly supported by the response to a historical perturbation. It also demonstrates that Thwaites' present-day mass loss trend cannot be reversed by ocean cooling alone, over policy-relevant centennial timescales.