I really hope these experts are wrong!
It would be a problem for many people (and for the whole nature I suppose)
And also I can't stand cold
Here in Maine the growing season has always been short and although they may not be the best tasting ever, there are lots of veggies that have been hybridized to mature quickly. We won't starve.
I agree with you 100% about the cold, though.
They are many ways to extent the growing season even for your area. It is really simple too, using the raised bed concept with dimensions like 4' wide x20' long beds.and use a "hoop" method to be able to plant a couple weeks earlier, and a few weeks later into the fall than you normally would.
Here is one example on how to do it, I would have the poles on the outside and into the ground at the base of the board.
How to Make a Hoop House for a Raised Bed
=====
If you really want to go the whole way, here is a video that combines watering, protecting and more in a permanent greenhouse set up for raised beds.
The only difference I would make is to use
GREY PVC pipe as it is made for above ground, resist Solar radiation damaging much better.
Tonyia's Tunnel Greenhouse - Raised Garden