It is 27 degrees today. Is it suitable for mountain climbing?

27 degrees is not suitable, it's too hot, it's easy to get heatstroke and if you have too much water on your back, it's also called a burden!

But if you climb a mountain higher than 3K,

It should still be ok, because with the increase of altitude, the temperature will drop

Generally, 23 degrees is more suitable for leisure mountain climbing.