1)Oceans act as a sink for warmth, it takes them a long time to warm or cool through their sheer volume. In 2017 they were the warmest ever recorded.
2)2017 was the second or third warmest year recorded, depending on which dataset was used. Of significance, 2017, was the warmest year recorded without the influence of an El Nino event.
3)The Arctic sea ice extent and volume have continued to decrease, the lowest extent in September was the eighth lowest ever recorded. Volume has changed downward by about 80% since 1979.
4)Antarctic is being investigated quite profusely at present, its sea ice has been at low levels. The huge 5,698 square kilometre Larson C ice sheet broke clear in July 2017. A number of major ice sheets are considered to be at risk as grounding lines are moving shorewards.