It takes just 4 years to detect human-induced ocean warming

Excerpt from the Guardian.com, Sept 2017

Global ocean heat content data isn’t as noisy as land-based and surface temperatures.  It represents the total thermal energy in the ocean waters, and is now known with a high degree of certainty (see the figure below), in part because scientists have improved ocean temperature sensing methods and increased the number of sensors throughout the ocean waters.

Increases in ocean heat content since 1950s.

Increases in ocean heat content since 1950s. Illustration: Cheng, L., K. E. Trenberth, J. Fasullo, J. Abraham, T. P. Boyer, K. von Schuckmann, and J. Zhu (2017), Taking the pulse of the planet, Eos, Vol. 98.

According to our analysis, the top 10 warmest years of ocean heat content are all in the most recent decade (following 2006) with last two years being the hottest. The heat storage in the ocean corresponds to 3×1023 Joules (a 3 with twenty-three zeroes after it) since 1960. Prior to the 1980s, values are not as well known, and the global record is unreliable prior to about 1960.

In the most recent 25 years, the Earth has gained approximately 0.7 Watts for every square meter of surface area. That may not sound like much but think about how many square meters are required to cover the surface of the Earth. To put these numbers in perspective, the heat increase in the oceans since 1992 is about 2000 times the total net generation of electricity in the USA in the past decade.

We believe, and argue, that ocean heat content is the key to quantifying how fast the climate is changing, and it has important implications for regional patterns of climate. According to Trenberth:

A key reason for the exceptionally active Atlantic hurricane season this year is because of the regional build-up of ocean heat along with its global warming component that fuels hurricanes.

“Ocean Heat Content” should become a standard metric not only for measuring climate change but for testing our computer models that are used to predict the future climate.