The amount of the heat absorbed by the ocean has doubled in the past 18 years, relative to the industrial era as a whole, reports a paper published online in Nature Climate Change this week. The study shows that approximately 35% of this heat has entered the ocean below a depth of 700 m, and continues to increase rapidly.

Peter Gleckler and colleagues use data from a variety of sources-including the nineteenth century Challenger expedition, more recent ship-based measurements and autonomous floats-to investigate how the heat content of the ocean has changed from 1865 to 2015. They consider the data in three depth sections: upper (0-700 m), intermediate (700-2,000 m) and deep (>2,000 m) layers. They then compare the observations to climate model simulations, and use the consistency between them to interpret changes over the industrial era.

This study provides temperature information across the full depth of the ocean, contributing significant data to our understanding of this understudied area, and highlights the importance of ocean monitoring programmes to track climate change.