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Monthly Ocean Heat Content and Temperature Anomalies Released

Pacific Ocean at sunset
Courtesy of NOAA Ocean Exploration

NOAA National Centers for Environmental Information (NCEI) has added monthly ocean heat content and temperature anomalies to its global ocean heat product suite. Climate models are often run on monthly intervals and require monthly heat content and temperature fields to best produce climate forecasts. Previously, ocean heat content and temperature anomalies were only available at a yearly, seasonal, and 5-year time-scale. The new, short-term monthly anomalies will help researchers understand this critical climate variable.

Warming Trends

The ocean absorbs excess heat from Earth’s system, acting to balance the excess heat from rising global temperatures. Ocean heat content has been on the rise since the 1960s and scientists have determined that the ocean absorbs more than 90 percent of the excess heat, which is attributed to greenhouse gas emissions. 

The increased ocean heat content coincides with increases in global average land and sea surface temperatures. Based on the annual Global Climate Report produced by NCEI, the January-December 2020 average global and ocean surface temperature was the highest since global records began in 1880. Warming trends in the ocean are likely to continue even if global average surface temperatures stabilize, according to research published in Advances in Atmospheric Sciences.

Graph of global ocean heat content change over a pentadal (5-year), yearly, seasonal, and monthly average by year. Courtesy of NOAA NCEI.

Tracking Ocean Changes

The most reliable method for calculating ocean heat content is through in situ (examining phenomenon and collecting data in the place where it occurs) ocean profiles of temperature. After World War II, technology for in situ subsurface ocean temperature measurements led to the development of a global ocean observing system. From the 1950s to the present, an increase in geographic coverage of temperature measurements has allowed scientists to collect ocean heat content estimates on an annual and seasonal time scale in the upper ocean. Only recently, in the era of global Argo profiling floats, do scientists have sufficient global coverage of the ocean to begin the exploration of global ocean heat content on a smaller, monthly time scale

Changes in ocean heat content are determined by comparing current in situ ocean temperatures to long-term averages, from the surface of the ocean to 2,000 meters deep. The uncertainty associated with the ocean heat content calculation is governed in large part by the geographic distribution density of temperature measurements. Uncertainty of the calculated ocean heat content will be larger for the monthly time period than for longer time periods, given the relative distribution of data.

Data for the analysis came from the World Ocean Database

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