Anomalously warm air temperatures in various parts of the world have been widely noted in recent decades. In marine systems, biological indicators such as the range of plankton and fish have been used to indicate impacts of ocean warming, although for many regions recent ocean warming does not exceed short-term warming events over the last two centuries. Here we use International Comprehensive Ocean-Atmosphere Data Set (ICOADS) sea-surface temperature data to update analysis in the North Atlantic to show that present warm conditions are currently no more persistent than those encountered in the last 150 years. We show that the position of various isotherms, which play a central role in influencing the distribution of marine taxa ranging from plankton to fish and turtles, are more regularly found further north in recent years than at any time since the 1850s.