https://www.nature.com/articles/s41586-018-0651-8

The APO [‘atmospheric potential oxygen’] data provide a much-needed independent confirmation of the recent upward revisions in estimates of ocean warming 5,9 . A higher value of ΔOHC [the change in global ocean heat content] compatible with both APO Climate and in situ temperature approaches (1.13 to 1.46 × 10 22  J yr −1 ) calls for a steric sea level rise of 1.34–1.74 mm yr −1 (Methods), in full agreement with satellite constraints on thermal expansion, corrected for the freshwater contribution (1.50 ± 0.40 mm yr −1 ) 8,23 .

A higher ΔOHC will also affect the equilibrium climate sensitivity, recently estimated at between +1.5 K and +4.5 K if CO 2 is doubled 1 . This estimated range reflects a decrease in the lower bound from 2 K to 1.5 K owing to downward revision of the aerosol cooling effect (in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report, as compared with the Fourth Assessment Report) 1,24 , but relied on a low ΔOHC value (0.80 × 10 22  J yr −1 for 1993–2010).

An upward revision of the ocean heat gain by +0.5 × 10 22  J yr −1 (to 1.30 × 10 22  J yr −1 from 0.80 × 10 22  J yr −1 ) would push up the lower bound of the equilibrium climate sensitivity from 1.5 K back to 2.0 K (stronger warming expected for given emissions), thereby reducing maximum allowable cumulative CO 2 emissions by 25% to stay within the 2 °C global warming target (see Methods).

tl;dr - Improved estimates of the heat gain by the oceans is constructed by measuring atmospheric O2 and CO2 content with high precision. From that, and working backwards, earlier estimates of heat gain by the oceans was low by about 25%, meaning that the climate is more sensitive to increases in CO2 than previously expected, and meaning that we're heading for +2K (+2C) warming minimum if things don't change.

Scary stuff.

Cheers,
Scott.