Carbon monoxide replaces some of the oxygen in your hemoglobin, and your entire body is automatically challenged.
Chronic carbon monoxide hardens the capillaries, preventing them from flexing with the pulse. This is hypertension. Your challenge with this is, it reduces blood circulation in your muscles.
When you are climbing, you raise your forearms to reach your hold, and you need those muscles for grip. Pretty soon they run out of oxygen (which is already reduced in your hemoglobin) and you're pumped.
So if you quit smoking today, then tomorrow you should expect more endurance.
But your entire body has been chronically challenged, and different tissues suffer in their own ways.
The blood supply in your skin is minimal. Well the follicles of your hair (all over your body) needs oxygen for its growth and maintenance. Eventually the chronic starvation kills the follicles, and you will see bald areas -- no not on your head: on your extremities. Starting on your toes and fingers, then on your lower legs. It looks like your athletic activity is causing the hair to get worn off, but in fact the hair is dead.
It's permanent. My lower legs are bald from that. In summer, folks ask me if I shave my legs? Also my fingers, and the backs of my hands.
I knew a guy whose skin went further than that. He started getting infection on his skin. It kept happening, and it wouldn't go away, because he couldn't get enough oxygen and white cells into his skin. Eventually gangrene set in, at different places and times, and they had to amputate first one leg, then the other. He never learned how to walk that way, he lived for a while in a wheel chair. I never saw him after that.
You can guarantee that you have some emphysema. It disables your lungs, starting at the bottom and working its way up. It's impossible to guess how advanced, not without a lung-function test. Emphysema is also permanent. You can still breath OK, but it takes longer to catch your breath -- your total endurance is compromised.
That's just the effects on climbing ability. But don't forget, you smell unpleasant, and all your friends know it.
Oh one more thing: money! In Canada, a pack of cigarettes costs $9.00 (I think) -- every pack is the price of a BD Stopper, or a DMM straight-gate biner. A carton of smokes would buy gasoline to drive you and your buddies to the crags and back for a month. Two cartons buys a pair of 5-10 climbing shoes.