How is humour created in ‘Climbing My Grandfather’?

By the juxtaposition of age and the image of a mountain in the central rock-climbing motif. The speaker, we would assume as a rock climber, is an adult. However, only a baby would be small enough to climb an adult. It is humorous for the reader to imagine an adult 'climbing' a senior, and conversely a baby climbing a mountain.

It is funny to think of a giant mountain-sized grandad that a grandchild could climb up, as though they are scaling a rock face. This imagery could symbolise the persona in the poem getting to know their grandad better as they get older and see the different parts of him. This is the more serious side of the poem underneath this humorous image.