What is the fine-grained topic of the following text: The concerns about recent trends on Greenland’s giant ice mass have been warranted, given signs of extensive surface melting and the possibility, explored here, that meltwater gushing to the ice sheet’s base through natural “drain pipes” called moulins could accelerate the flow of ice to the sea (click here for more information). Only return the topic.
Greenland's ice mass melting trends and its potential effects.