> Primarily vegetarian diets and less driving would make mountains of difference for the world.
Changing diets yes. Changing driving habits, not really. Personal use of passenger vehicles accounts for a tiny fraction of transportation related CO2 emissions. The overwhelming majority comes from cargo ships and associated logistics.
A typical cargo ship will burn about 30 liters of bunker fuel (far more polluting than diesel) to travel 1 meter. 15 typical cargo ships emit as much CO2 as all cars on the planet combined. There are about 15,000 such ships operating today, with a further 30,000 slightly smaller ones. A single cruise ship company like Carnival Cruise emits more CO2 than all of Europe's car's combined.
Even if the entire world converted to zero-emission EVs overnight, it wouldn't make a meaningful dent in these numbers.
The inconvenient truth is that in order to make a serious dent on transportation related CO2 emissions, the entire developed world would have to give up its lavish lifestyle of internationally shipped products and foods. Sadly a harder sell then 'drive an EV to save the planet lol', so our governments continue to focus on inconsequential but easily attainable measures. And that is nothing to say of the fact that cutting down international shipping is at odds with free market capitalism that's driving our civilisation.
Fun fact: bulk carrier shipping is so cheap that in Australia, locally caught fish are shipped to China for processing and freezing and then shipped back here for retail. The pollution associated with this alone is more than the sum pollution of all Australian cars.