Upper-ocean heat content anomaly linear trends for 1993–2019. Annual estimates of the PMEL combined maps. Values are in W m-2 (colour bar) applying 90% two-tailed (5–95%) confidence limits to outline areas with trends that are statistically significantly different from zero (black contours). Latitudes are gridded at 30° intervals, and longitudes, centered on 150 °W, at 60° intervals (dotted lines). OHCA, ocean heat content anomaly.
Johnson, G.C., and J.M. Lyman, 2020: Warming trends increasingly dominate Global Ocean. Nature Clim. Change, 10, 757–761. https://doi.org/10.1038/s41558-020-0822-0
Ocean warming absorbs about 9/10th of the excess energy that is entering Earth’s climate system because of a build-up of man-made greenhouse gasses in the atmosphere. That warming causes ocean expansion, contributing to sea level rise. Knowing how much, and where the ocean is warming is vital for validating climate models, predicting climate change, assessing sea level rise, and understanding changing marine ecosystems.
Johnson and Lyman (2020) analyze over 15 years of near-global, high-quality, in situ ocean temperature measurements from the Argo array coupled with other historical data and 27 years of sea surface height anomalies from satellite altimeters. Their work illuminates patterns in global warming from 1993 to 2019 in the upper (0–700 meters) ocean (see figure). Over that 27-year time period, statistically significant warming trends (red areas outlined in black) are found over 56% of the ocean surface, whereas statistically significant cooling trends (blue areas outlined in black) only comprise 3% of the ocean surface. The cooling area in the northern North Atlantic Ocean may be associated with a slowdown in the Atlantic Meridonal Overturning Circulation linked to global warming. In contrast, when all possible 5-year trends from 1993–2019 are evaluated, the statistically significant warming and cooling areas amount to 24% and 17%, respectively. The longer the time period over which the trends are calculated, the more of the ocean is found to be warming.
For more information or to read the full article, visit the article page at Nature Climate Change.