I had previously heard that category 5 storms were originally thought to be impossible, and only became possible due to global warming adding more energy into t

I had previously heard that category 5 storms were originally thought to be impossible, and only became possible due to global warming adding more energy into the atmosphere. The article however states that category 6 was technically possible as far back as 1979. Have these category 5, 6 and maybe higher always been possible, but just more improbable?