Is it bad to leave him in the car?

My dog has severe separation anxiety. He cries the entire time I'm gone and then destroys stuff. He loves riding in the car so I bring him with me almost everywhere as long as it's nice weather. I leave the windows cracked and have blankets and a sweater for him when it's cold, when it's warm I leave the car on with the AC going. It's usually no more than 30-45 minutes and he loves people watching. Is it bad to leave him in there while we go to lunch for an hour? It winter but not super cold here. About 60 degrees. What's the longest you would leave your dog in the car?

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