Alex, in California, the needs of climbing roses are not great.

For the first three years, pruning should be MINIMAL.
You can shorten the lateral canes -- NOT the long, main, basal canes!
Cut those laterals down to perhaps 6 bud eyes.
When you get done shortening them, you will have removed the greater part of the leaves.

Yes, you really should remove the rest of them.
If you're not up to it, spray the foliage, along with the rest of the plant with a good dormant oil spray.
Sun, and the next Santa Ana wind should remove most of the rest.

Jeri

It sounds like your climbers are young, in the ground a year or two, is that right? Young climbers don't need much pruning. They need to establish, which generally takes them longer to do than HTs or floribundas.

This is the general scenario of how climbers develop in my zone 9 garden and how I deal with them. Your milage may vary depending on the climber, the climate, and the care.

Growing season #1: climber produces a few less-than-full sized canes and blooms a little. Towards the end of the growing season the climber might produce one or two mature sized canes (the advertised size) that look way out of proportion to the rest of the plant.

Pruning after season #1: remove dead, diseased, damaged wood only. Arrange canes so they don't interfere with or damage each other. There may not be enough canes to make a good balanced fan on the support.

Growing season #2: climber produces some mature sized canes and blooms moderately. Side shoots (laterals) may be produced by the mature-sized canes, with flowers at the end of each lateral.

Pruning after season #2: remove dead/diseased/damaged wood, tip-prune the laterals that bloomed, shorten some laterals only as necessary (damage, grossly out of proportion, etc). Arrange canes as well as can be expected, so they don't interfere with or damange each other.

Growing season #3: Climber produces several new mature sized main canes of greater diameter than year #2, and blooms pretty well off of multiple lateral shoots on each mature-sized cane.

Pruning after season #3: I remove all the less-than-mature sized canes that grew the 1st year, trim the side shoots (laterals) coming off the canes grown in years 2 and 3, and then rearrange all the canes nicely on their support, because there are now enough good big canes do do a good balanced job of fanning out evenly on the supporting structure.

Growing season 4 and thereafter: Very good to excellent bloom. Plant produces a new large basal (main) cane or two.

Pruning after growing season #4: I completely remove 1 or 2 of the oldest least productive large canes right down to the base. I trim back all the laterals and may remove some laterals that are looking old. On some roses I remove all the short laterals because they are not that productive the next year, on others I leave them, because they are productive. Ideally you entirely remove 1 or 2 large canes and the climber grows 1 or 2 new ones as replacements, so the climber is continually renewed.

On some roses, the laterals remain short and I attach only the main canes to the support. On other roses the laterals can get as long as the main canes, and I may have main canes and long laterals all tied to the support, as is the case with this Sombreuil:
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This Sombreuil is 6 years old from a Vintage band and is freshly pruned down to about 16' wide and 9' tall at the tallest point. You can see a couple of short laterals that I missed if you look carefully. The stucco part of the fence is 4' and the iron adds another 2' so the fence overall is 6' tall. It took me about 8 hours to prune it all, take it all off the fence and retie it back on.

If your climbers are young, those 12' canes of yours have side shoots coming out of them, you might need to shorten the side shoots. If they don't have side shoots yet, they don't need any cutting back unless there is damaged, diseased, or dead wood, which should be removed. If the wood all looks good, leave it.

As far as the foliage is concerned, I look at the new axial buds swelling at the base of each leaf. If the swelling is pretty far advanced, last year's leaves are getting ready to fall off. I cut off or knock off the old foliage and put it in the trash because it usually has a bit or a lot of Rust at that point. I would rather have the Rust go into the trash than back into the garden.

Of course the old leaves will eventually fall off by themselves, but a mix of new and old foliage looks really bad to me. I like to start with a clean slate. Just my personal choice.

Well, hope that helps. This is my experience in zone 9, others will have different experiences to share.