Potentially Diesel has less CO2 emissions than Petrol if that is the point you want to insist on.
The major issue with Diesel is NO2 emissions, on top of respiratory issues directly attributed to NO2 in city centres, NO2 is also a reducer of human longevity. [0]
I would say anything that is slowly killing us and reducing our lifespan should be pretty high on our priorities list.
Is diesel CO2+NO2 is worse than petrol CO2+NO2 for global warming?