The wildlife expert was talking on Friday Night With Jonathan Ross when the Himalayan phenomenon was raised.
"I'm baffled by the Abominable Snowman - very convincing footprints have been found at 19,000ft. No-one does that for a joke. I think it's unanswered," he said.
Global warning was also raised, with Sir David claiming that there is "no way back".
"Before, it was thousands of years and now it's decades...but we can slow down the rate at which we change," he said.