Slower warming in the deep ocean encourages a perception that its biodiversity is less exposed to climate change than that of surface waters. We challenge this notion by analysing climate velocity, which provides expectations for species’ range shifts. We find that contemporary (1955–2005) climate velocities are faster in the deep ocean than at the surface. Moreover, projected climate velocities in the future (2050–2100) are faster for all depth layers, except at the surface, under the most aggressive GHG mitigation pathway considered (representative concentration pathway, RCP 2.6). This suggests that while mitigation could limit climate change threats for surface biodiversity, deep-ocean biodiversity faces an unavoidable escalation in climate velocities, most prominently in the mesopelagic (200–1,000 m). To optimize opportunities for climate adaptation among deep-ocean communities, future open-ocean protected areas must be designed to retain species moving at different speeds at different depths under climate change while managing non-climate threats, such as fishing and mining.

深海变暖的减慢使人们认识到，其生物多样性比地表水更少受到气候变化的影响。我们通过分析气候速度来挑战这一概念，该速度为物种的范围变化提供了期望。我们发现，深海的当代（1955-2005年）气候速度快于地表的速度。此外，在所考虑的最积极的温室气体减排途径（代表浓度途径，RCP 2.6）下，除了地表以外，所有深度层的未来（2050-2100年）预计的气候速度都更快。这表明，尽管缓解措施可以限制气候变化对地表生物多样性的威胁，但深海生物多样性面临着不可避免的气候速度升级，其中最突出的是中生代（200–1,000 m）。