Final answer:
The subject of this question is Geography, discussing the changes in summer and winter sea ice extent since 1979.
Step-by-step explanation:
The subject of this question is Geography. It is discussing the changes in summer sea ice minimum extent and winter sea ice maximum extent since 1979. The information provided indicates that there has been a decline in both summer and winter sea ice over the years, with factors such as global warming and climate change playing a significant role in these changes.