> we could have made modest changes back in the 70’s and even 80’s and it could have been no big deal

Unlikely. Even by the 1960s petroleum had become our way of life, globally (with rare exceptions if we want to account for Amazon rainforest tribes & so on). Jevon's paradox holds that any attempt to decrease our consumption of oil or coal, say by producing more nuclear power generation, would simply make it more affordable for under developed countries to use instead.

And in any case; nuclear power does not give us the fertilizer our crops depend on, and electric transportation -still- is not advanced enough to obsolete our big rigs & seafaring container ships.

And those oil guzzling container ships are one of the planet's biggest sources of greenhouse gases. They are dirty in emissions and inefficient in oil/fuel consumption. The top 10 worst container ships in use -right now- nevermind 40 years ago, EACH emit as much greenhouse gas as all of the cars in North America.

Now I suppose in theory we could have banned petroleum based products (coal, gas, diesel, etc) after WW2 and tried to use the UN to invade & stop any country globally from using them, but I am skeptical that this wouldn't have caused WW3 and nuclear war in short order...