Accelerated Ocean thermal expansion and its contribution to Global Sea-level rise

Abstract

Global ocean heat content (GOHC) changes are crucial to understanding climate change, as oceans store about 91 % of the excess heat in the climate system. The thermal expansion of oceans significantly contributed to sea level rise in the twentieth century and will likely remain a major factor in the twenty-first century. This study analyzed decades of data from global ocean reanalysis and satellites, revealing that from 2014 to 2023, the annual rates of increase in GOHC and global mean sea level (GMSL) were 45.2 ± 1.78 MJ/m² and 4.7 ± 0.23 mm, respectively. These rates are 1.7 and 1.8 times higher than those of the previous four decades. Thermal expansion alone accounts for 56 % of the total GMSL rise. A 1 °C increase in global ocean temperature would result in a 0.89-m rise in GMSL due solely to thermal expansion. GOHC variations align with GMSL changes monthly, though a three-month delay is observed in regions such as Southwest China, the Indochinese Peninsula, and the coastal Middle East. Significant increases in both GOHC and GMSL are most evident in the 20°N–40°N and 20°S–40°S regions. Since the late 1980s, greenhouse gas emissions have overtaken solar radiation as the primary driver of ocean temperature increases. Since the 1990s, the Earth's energy imbalance (EEI) has remained positive, with an annual increase of 0.03 ± 0.016 W/m², indicating excess heat accumulation.