I'm a pre-law student with a strong humanities background. Unfortunately, it seems that intellectual property law has become an area of interest to me. Will I be disadvantaged by my lack of a science background if I eventually decide to practice in this area?

Depends on the area of IP that interests you. To become a patent attorney, you do need a science or engineering background; however, there is no such requirement to be a patent litigator. Other aspects of IP (copyrights, licensing, contracts (for buying and selling IP), etc.) do not require a science background.

If you're smart and interested enough to dig in and understand the technology and issues, no.

The answers given so far are pretty good but I'd just add that you will definitely be at a significant disadvantage when/ if you look for your first job in any patent or tech oriented ip field. I was in the same position when I started working and no one wanted to talk to me about my doing ip work. I'm in tech licensing now though, so you can get there, or somewhere close to there, but you will be at a disadvantage for sure when you're first starting out. Also a caveat to the answers stating that you can practice trademark or copyright law--those jobs are far more scarce than patent law related jobs, and programming/CS related law (eg licensing, etc) is still regarded as technical enough to benefit from a science degree as well.

Absolutely not.  I have been doing copyright and trademark work for 27 years and my BA is in politica lscience.  To be a patent lawyer, however, you have to pass the separate patent bar which requires a sceince courses.  People I've known who become patent lawyers have backgrounds in engineering or math.  Because there are frequently trademark and copyright issues that arise with patents, many patent lawyers also practice in these areas.  I hope that helps.