A large-ensemble reanalysis system (CIGAR) reveals that ocean warming from 1961 to 2022 was 0.43 ± 0.08 W m⁻², with a statistically significant acceleration of 0.15 ± 0.04 W m⁻² dec⁻¹, peaking at high latitudes. In 2022, 11.6% of the global ocean reached its highest OHC, nearly doubling previous years. Regional uncertainties are highest in the Tropics, while global uncertainties are 40% before and 15% after the mid-2000s. Uncertainty in regional trends is mainly due to observation calibration (high latitudes) and sea surface temperature data (low latitudes). Ocean warming threatens marine environments through sea-ice decline, sea-level rise, and marine heatwaves, alongside ocean acidification. Ocean warming is non-uniform, driven by atmospheric heat uptake and multi-scale redistribution. OHC is a key climate indicator, with long-term increases due to anthropogenic emissions. Pre-Argo uncertainties are dominated by observations, with horizontal mapping and vertical interpolation as significant sources. Model-based reconstructions are affected by physics parametrization and systematic errors. Objective analyses and reanalyses differ in their treatment of ocean models and data assimilation. CIGAR shows enhanced interannual variability and a pronounced non-linear OHC increase, with the first period (up to 1997–2000) exhibiting slower warming. CIGAR agrees with other assessments in OHC trends and shows smaller uncertainty. The reanalysis system confirms the reliability of OHC estimates and identifies major sources of uncertainty, including observation bias, SST data, and atmospheric forcing. The study highlights the importance of accounting for uncertainties in OHC reconstructions for climate monitoring and understanding. CIGAR's results provide a comprehensive view of ocean warming and its uncertainties, emphasizing the need for ensemble reanalyses to capture multi-decadal climate changes. The study also shows that the 1961–2022 warming is 0.43 ± 0.08 W m⁻², with a significant acceleration of 0.15 ± 0.04 W m⁻² dec⁻¹. Regional patterns show dominant trends and acceleration at high latitudes and near the Equator, with mid-latitudes exhibiting less pronounced accumulation. The 2022 OHC increase is widespread, with over 11% of the global ocean showing its highest OHC. Before the Argo era, the Tropical band had the largest OHC uncertainty, partly linked to El Niño events. Global uncertainty reduced from 40% in the 1960s to 15% in the last decade. Regional trends are mainly affected by observation procedures and SST data, while all sources contribute to global trendA large-ensemble reanalysis system (CIGAR) reveals that ocean warming from 1961 to 2022 was 0.43 ± 0.08 W m⁻², with a statistically significant acceleration of 0.15 ± 0.04 W m⁻² dec⁻¹, peaking at high latitudes. In 2022, 11.6% of the global ocean reached its highest OHC, nearly doubling previous years. Regional uncertainties are highest in the Tropics, while global uncertainties are 40% before and 15% after the mid-2000s. Uncertainty in regional trends is mainly due to observation calibration (high latitudes) and sea surface temperature data (low latitudes). Ocean warming threatens marine environments through sea-ice decline, sea-level rise, and marine heatwaves, alongside ocean acidification. Ocean warming is non-uniform, driven by atmospheric heat uptake and multi-scale redistribution. OHC is a key climate indicator, with long-term increases due to anthropogenic emissions. Pre-Argo uncertainties are dominated by observations, with horizontal mapping and vertical interpolation as significant sources. Model-based reconstructions are affected by physics parametrization and systematic errors. Objective analyses and reanalyses differ in their treatment of ocean models and data assimilation. CIGAR shows enhanced interannual variability and a pronounced non-linear OHC increase, with the first period (up to 1997–2000) exhibiting slower warming. CIGAR agrees with other assessments in OHC trends and shows smaller uncertainty. The reanalysis system confirms the reliability of OHC estimates and identifies major sources of uncertainty, including observation bias, SST data, and atmospheric forcing. The study highlights the importance of accounting for uncertainties in OHC reconstructions for climate monitoring and understanding. CIGAR's results provide a comprehensive view of ocean warming and its uncertainties, emphasizing the need for ensemble reanalyses to capture multi-decadal climate changes. The study also shows that the 1961–2022 warming is 0.43 ± 0.08 W m⁻², with a significant acceleration of 0.15 ± 0.04 W m⁻² dec⁻¹. Regional patterns show dominant trends and acceleration at high latitudes and near the Equator, with mid-latitudes exhibiting less pronounced accumulation. The 2022 OHC increase is widespread, with over 11% of the global ocean showing its highest OHC. Before the Argo era, the Tropical band had the largest OHC uncertainty, partly linked to El Niño events. Global uncertainty reduced from 40% in the 1960s to 15% in the last decade. Regional trends are mainly affected by observation procedures and SST data, while all sources contribute to global trend