"Heat accumulation" refers to the process of heat building up or gathering in one place over time. It means that the amount of heat in a specific area or object is increasing gradually. Full definition
It indicates that there has been no decline at all in the rate of heat accumulation in the climate system as a whole... if I understand things correctly. (realclimate.org)
Several studies in recent years have shown an acceleration in the rate of heat accumulation in the oceans. (realclimate.org)
An early ramp up with fully eight and a half decades left to go in a Century that will certainly see substantial further increases in global heat accumulation. (robertscribbler.com)