Answer:
Personification.
Step-by-step explanation:
Personification is the giving of human attributes or characteristics to some non-human or abstract ideas or themes. Such an act allows the writer to provide more 'color' or 'body' to their work, enriching it in such a way that it appeals to the thinking and imagination of the readers.
In the given sentence "Lofty mountains that pierce the clouds and reach to dizzying heights may appear to us humans as coldly majestic, lonely, even forbidding".
The use of the word "lofty mountains that pierce the clouds" seem to imply that the mountains have feelings, like a feeling of aloofness, while at the same time "reach to dizzying heights" signify the ability to literally try to reach or touch as humans do. These factors all suggest the use of personification where these mountains are given the characteristics of humans like the ability to feel lonely, the ability to reach something, etc.