The most common and most likely answer to this crossword clue is the 6 letter word KOALAS
I've seen this crossword clue in Financial Times
K
O
A
L
A
S
More clues leading to the result KOALAS
Buddy explains!

The straight part
We know that "Climbers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case climbers = koalas.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KOALAS mean?
KOALAS noun- A tree-dwelling marsupial, Phascolarctos cinereus, that resembles a small bear with a broad head, large ears and sharp claws, mainly found in eastern Australia.