Do climate change experiments yield relevant insights into responses to chronic ocean warming?

Climate change threatens ocean biodiversity. Studies aimed at predicting responses of marine species to chronic warming increase temperatures to levels expected in the future. Using a meta-analysis, we ask whether ramping rate (i.e. the speed at which organisms are brought from ambient to experimental temperatures) modulates these responses. A systematic review yielded 175 experiments from 48 studies. One-third of studies had no ramping period; those that did used rates of warming faster than those observed during marine heatwaves. The effect of ramping rate on responses to warming varied. The decline in reproduction observed under warmed conditions when there was no ramping attenuated when temperatures were increased more slowly. Warming decreased survival, whether there was a ramping period or not. The effect on abundance switched from positive without ramping to negative with slower ramping, and photosynthesis declined as ramping rate slowed. The magnitude of temperature change influenced responses more consistently than ramping rate, but their relative importance varied with response type. We conclude that experiments aiming to predict the effects of chronic warming simulate instead the effects of acute heat stress. Marine communities naturally exposed to predicted future conditions likely provide the best insights into the effects of chronic ocean warming.