Vertical climate velocity adds a critical dimension to species shifts

Climate responses of marine organisms differ from those on land as marine species have the flexibility to move vertically. While horizontal climate velocity has been used to predict poleward range shifts, many species are not moving as expected. Incorporating shifts in depth, which have received less attention, may better explain climate responses of marine organisms. Here we assess vertical and horizontal climate velocities across 63 global large marine ecosystems and find that 77% of vertical climate velocities are negative, reflecting isotherm deepening. Vertical climate velocity is 10,000 times smaller than horizontal climate velocity, allowing organisms to maintain constant temperatures by shifting metres in depth rather than kilometres horizontally. Within three key large marine ecosystems, we find more species shifts are explained by vertical than by horizontal climate velocity. Together, our findings have implications for understanding species adaptation to change and for future accessibility of marine resources.