Yes and no, farming strategies for different area will have to change as the conditions do. People who suddenly find themselves in a drier area will have to adopt techniques and practices better suited to dry conditions. People who find themselves in wetter areas will have to shift to crops that hold up better under wetter conditions. Instead of the current practice of being able to try to grow just about everything everywhere and brute forcing it by artificial means(often with lots of irrigation water) when needed.
Therefore, disruption.
Opportunity cost.
Natural Variability of climate.
Adaptability.
The climate varies over centuries without respect to activities undertaken by man. It is an unavoidable fact of life, and we have 1, and arguably 2 stark examples of that in North America alone. For that matter, the Roman Empire arguably bore witness to it as well as the Vikings centuries later.
Taking steps to mitigate any disruption that may occur
is always a smart play, so long as the measures are "within reason." The "within reason," limiter is key. If the costs of taking the mitigating measures far exceeds any likely cost I'm likely to incur from having done nothing, then that particular mitigation option isn't viable and should be ignored.
Because hey, a 777 might fall out of the sky and crash into my house. I
could theoretically have my built to such a specification that it could survive a direct hit in such a scenario. But realistically, it'd be more cost effective for me to set that extra money aside, buy some regular insurance policies, and in the event that my house does get destroyed by having a jetliner crash into it, I just build a new house. Because the cost multiplier of having my house built as an above-ground bunker just doesn't make it viable as a top-shelf mitigation option.
But if my house is on a floodplain, then it wouldn't be unreasonable for me to budget up to a significant fraction of the house's value into taking proactive measures to protect it against a 100 year flood event, or even going for a 200 or "500 year" event depending on how the costs scale as you move up the chain. Of course, in this case, we're into moral hazard territory as your neighbors would think you're crazy, up until they get flooded out and you're high and dry. Because well "That's what we have flood insurance for" while ignoring the whole matter of the whole idea behind insurance is to
never need to use it.
From my perspective, a LOT of the push going on with AGW is the "build a bunker to withstand the 777" approach, rather than latter option. What is being pursued in many cases just is not reasonable.
To put it a different way, they're basically telling someone that just qualified as an Olympic Sprinter that in order prevent a health issue they'll develop in 30 years, we need to cut their Achilles Tendons next week and reattachment can never happen. Of course, that means the sprinter can't compete. What do you think their response will be?