If you are unable to deduct charitable contributions due to the AGI limitations in the current tax year, you may be able to carry forward the excess amounts to future years.

Per IRS Publication 526 Charitable Contributions, on page 19:

Carryovers

You can carry over any contributions you can't deduct in the current year because they exceed the limits based on your adjusted gross income (AGI). Except for qualified conservation contributions, you may be able to deduct the excess in each of the next 5 years until it is used up, but not beyond that time.

A carryover of a qualified conservation contribution can be carried forward for 15 years.

Contributions you carry over are subject to the same percentage limits in the year to which they are carried. For example, contributions subject to the 20% limit in the year in which they are made are 20% limit contributions in the year to which they are carried. But see Carryover of capital gain property, later.

For each category of contributions, you deduct carryover contributions only after deducting all allowable contributions in that category for the current year. If you have carryovers from 2 or more prior years, use the carryover from the earlier year first.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.