The answer is simple in concept, hard in execution.
Grow local and heirloom varieties.
Save seeds from the strongest plants to grow the next generation of plants.
Because the strongest plants will be those best adapted to the climate as it is when you grow them, if you keep selecting seeds from the strongest plants, your garden will gradually adapt along with the changing climate.
Think of it as evolution in action.
If you're trying to figure out what Monsanto branded hybrid monocultures will best survive climate change, you're doing it the wrong way.