Earnings on non-deductible contributions in Traditional IRA

I have non-deductible contributions in my Traditional IRA (yes, not the smartest thing. Should have just put it into a ROTH IRA).

It's been several years and I can't make any amendments now, but I want to convert the whole thing to a ROTH IRA. How should I go about treating the earnings on my non-deductible contributions? Are they taxable or not?