Circuit training is invaluable when done well, not only does it take less time which many people have very little of but you not gain strength and also a CV benefit from this style of training. As well, it may more accurately mimic what your body is going through when climbing demanding terrain.

How to build a circuit: this can seem challenging and often is so once again I will keep it simple to begin:
Four to five exercises combining these critical components:

• Squat: (ex) squats, dead lifting, lunging, step-ups, box jumps, side lunging
• Sit: (Core) sit ups, back extension, rotational strength, leg raises, med ball throws, and balance
• Push: Push-ups, dips, over head press, bench press
• Pull: pull ups, high pulls, cable rows, bent over row
• Metabolic (optional): rowing machine, running intervals, jumping rope

These are all the functional Ranges of Motion that our bodies can and do work in. We have to train them all and in harmony with one another. You will rapidly discover that a weakness in one area will diminish your capacity to perform specific movements. We want to train away those weaknesses. Those weaknesses are what will lead to inability to perform any complex endeavor such as ice climbing, skiing, and biking, at your absolute best.

I always put Strength and Flexibility or ROM (range of motion) together because they should be inseparable in your training. Simply put, your muscles have a functional ROM in which they can apply force, that functional ROM is determined by your level of flexibility. It is that simple. Gymnasts, Martial Artists, Dancers are a perfect example; most people are impressed by the display of strength of these sets of athletes. As well, most injuries (unless they are the result of trauma) occur when there is an imbalance in either strength or flexibility in the system. My experience has shown that the first aspect of training many athletes fore go is stretching or increasing functional ROM.
The most important point I want you to take away from the following segment is that of training the system as a whole. Muscle isolation exercises are inappropriate for anyone but a body builder, the elderly, inexperienced population or injury rehab. We as athletes do not ever use our muscles in isolation. We use our bodies in complex movements, ergo: we need to train our bodies using complex movements, challenging our strength, increasing our flexibility, testing our balance, and opening new neuromuscular pathways.

Simple ROM to work on:
After a warm up and in between sets you should stretch.

• Aboriginal Squat: this is a full squat with your heels on the floor, toes relaxed, and torso upright. You can prepare for this by stretching your hamstring, quads, and calves in a traditional manner, however we want the flexibility to equate to a functional ROM for an exercises like Squats, dead lifting, lunging, step ups, box jumps etc.

Imagine climbing, you can only pull your leg up and stand in relation to the body as far as you can squat down and stand up.

• Arms Over Head: Can you stand up right and hold your arms straight over head, elbows even with your ears, without arching your low back or lifting your shoulders? If yes, great! If not, this is a ROM we need to develop. Practice an overhead squat with a stretching belt or dowel rod over head, between your hands.

Imagine swinging an ice axe overhead with enough FORCE to penetrate the ice, you need all your functional ROM to generate enough force correct? Perfect correlation to the sport, you will be able to swing that ice axe more effectively if you can access all of your functional strength.

• Chest Opening: Stand in a doorway, door open, place your arms out at 90 degrees, elbows just below shoulder height and step forward to stretch your chest/pectoral muscles. This will help with posture, delivery of force from the muscles of the back and shoulders, and breathing capacity (making room for your lunges to expand with air).
• Hip Opening: Frog stretch on the floor or against a wall. Lean against a wall, move your feet/legs as far away from one another as they will reasonably go, squat down so your legs are at 90 degree angles. Place your hands on the inside of your legs open them further while holding the squat position, hold this for 30 sec to 2 minus. Repeat.
• Rotation of the body: Back lying twist. Lying on the floor, raise your knees to your chest, then bring you feet up so your legs make a 90 angle, move you knees away from your chest until they are over you hips. Keep you right shoulder on the ground as you let your lower body twist to the left try to touch your left knee to the floor. Repeat opposite side. You can do this with your legs straight as well, it makes it more difficult to bring your legs back to center.

These are examples of ways to increase flexibility in these key areas.
If you aren’t sure about how to stretch and gain ROM in these areas, I highly recommend taking a GOOD yoga class. Yoga not only develops strength and flexibility, but teaches you to become more body aware and has elements of relaxation and meditation. Some of the mental components that are beneficial to being/becoming a climber.