Global warming is attributed to human activities that potentially cause record warm sea surface temperatures (SSTs) worldwide. However, to what extent climate change has altered discrete extreme ocean warming (EOW) around Japan remains unclear. Here, we show the impact of global warming on EOW events (high SSTs less frequent than once per 20 years at the preindustrial level) surrounding Japan in each calendar month for 1982–2022 using climate models. In contrast to the gradually increasing occurrences of EOW events, the most frequent events occurred in approximately 1998 and the mid‐2010s, especially in southern Japan. We found climate change was not yet dominant in the 1998 events but has multiplied the occurrence probability of most events by at least twice since 2000. Furthermore, we estimated that the possibility of the future normal climate exceeding record high SSTs can be sharply reduced by limiting global warming from 2°C to 1.5°C. Plain Language Summary Human activities have warmed the Earth's surface since industrialization, so we have often experienced unprecedentedly high sea surface temperatures (SSTs) worldwide. However, it is still challenging to quantitatively understand how much long‐term climate change has affected the probability of discrete extreme ocean warming occurrences in specific regions. In this study, we used multiple observational datasets and climate model simulations to identify monthly extreme sea surface warming events that occur around Japan less frequently than once every 20 years under preindustrial climate conditions. Extreme warming events gradually become more frequent as global warming progresses, but a large number of these events episodically emerged in approximately 1998 and the mid‐2010s. This is more evident on the southern side than on the northern side of Japan. This study revealed that natural variability mainly caused extreme warming events in 1998, but climate change has been the dominant factor driving extreme warming events since 2000. We also estimated the future change in the chances of experiencing SSTs warmer than the highest records. Our results pointed out that the ocean surface surrounding Japan would exceed the present record high temperatures every 2 years unless global warming could be suppressed from 2°C to 1.5°C. Key Points The contribution of climate change to discrete extreme ocean warming (EOW) from January 1982 through July 2022 around Japan is estimated The occurrence chance of EOW is generally higher in southern Japan, more than doubled since 2000 due to climate change Limiting global warming from 2°C to 1.5°C sharply reduces the possibility of normal climate exceeding record warm ocean surface