During the year, the global
monthly ocean temperature anomaly ranged from +0.58 °C (+1.04 °F; February) to +0.86 °C (+1.55 °F; October), a difference of 0.28 °C (0.51 °F).
My amateur spreadsheet tracking and projecting the
monthly NASA GISS values suggests that while 2018 and 2019 are likely to be cooler than 2017, they may also be the last years on Earth with global average land and
ocean surface
temperature anomaly below 1C above pre-industrial average (using 1850 - 1900 proxy).