Human-induced emissions have driven the Earth into an energy imbalance, resulting in the accumulation of excess heat within the climate system. Approximately 90% of this surplus energy is absorbed by the global ocean, causing ocean warming and making Ocean Heat Content (OHC) a key indicator of climate change. However, accurately quantifying OHC remains difficult due to the evolving observing system, significant methodological differences, and varying data processing approaches. Despite its essential role in climate monitoring, there are currently no established guidelines for calculating the OHC indicator. In this presentation, we review the main challenges in estimating OHC and emphasize the urgent need for a coordinated international effort to establish the first set of recommendations for OHC assessment. A robust and consistent methodology is crucial for tracking past, present, and future climate change, and for addressing the pressing question of global warming acceleration. Our speaker Audrey Miniere works at Ecole Normale Supérieure (ENS). "I am a postdoctoral researcher at the Laboratoire de Météorologie Dynamique (ENS, Paris), working on ocean warming. My research focuses on its spatial and temporal distribution and its estimation using a variety of observational data, including in situ measurements, satellite observations, and reanalyses. I work with Prof. Sabrina Speich and Dr. Karina von Schuckmann". What is a Climate Coffee? #climatecoffees are short (circa 40 min: 20 min talk + 20 min Q&A), relaxed meetings for scientists to share ideas, discuss methods, and communicate new results. They are open to speakers of all seniority; we especially encourage early-career scientists to become speakers. The Coffees are an exciting opportunity for scientists to build a network and disseminate recent results peer-to-peer. We invite researchers from across the climate science community to join us for this series of regular online knowledge exchange events. Recording of the presentation: You can watch the recording on YouTube: https://youtu.be/GXL5MiwepuQ Organisation The Climate Coffees are organized by the Horizon Europe projects ObsSea4Clim, OCEAN ICE, the National Center for Climate Research - DMI Danish Meteorological Institute and the European Climate Research Alliance.