Joe,
That is the $ 65,000 question that no one will give an honest or strait answer to .
Every one selectively quotes statistics to enhance their position so basically every one lies.
What you have to get your head around is ENERGY is FOREVER and all energy ultimately has come from the destruction of matter.
Thus ultimately , apart from bombs & nuclear power, all the rest of the energy we consume has it's origins in our sun .
From then on all we do is convert it from one form to another and every time we convert it heat is a waste product .
And HEAT is the big problem that has finally come home to roost because from the dawn of time heat was simply dumped into the atmosphere or water .
And because the volume of heat was small and the volume of the atmosphere & oceans was vast the tiny incrimental increases were not noticed and not a problem
Every thing you do converts some form of energy to heat and that heat has to eventually b radiated into outer space from the atmosphere or the atmosphere gets hotter.
And the problem is the heat, not the CO2 , although the CO2 reduces the speed that the atmosphere can raadiate the heat you converted into space .
As for battery power , it is filthy if you take your starting point the mines that extract the raw materials that go into making the batteries right through to the disposal of the dead batteries
Petrol is actually less polluting overall even more so if the mower is manufactured from reclaimed materials .
As for energy conversion to electricity because we don't actually produce energy we just convert chemical , gravitational , wind , solar or mechanical energy to electricity every single one of the process generates pollution and in most cases, that which has a small pollution quotent at the generation stage has a massive pollution quotent at the manufacturing stage and visa versa.
Atomic energy produced the second lowest amount of pollution per Kw of electricity used , but when you look at the steels & concrete used to make a power station, it has to generate a lot of power for a long time to get to the break even point.
The other problem with atomic energy is it convert matter into heat so actually generates more heat both directly at the power station and at the consumption end when all that electricity heat or houses or drives our computers.
Hydro is the least polluting pre Kw produced but then you have the environmental damage from the building of dams and the problems at the water discharge end.
Waterwheels are probably the best for the environment , particularly if they are made of wood .
Any one who thinks they are environmental heros for using battery powered anything are deluding themselves .
If you want to be environmentally benign then use a corded mower or a sythe .
The biggest problem is people are lazy and thus stupid so we jump on a popular band waggon without any thought of the consequences.
So right now it is LESS CO2 so ask anybody and they will happily tell you once we get to zero CO2 emissions it will be back to life as we used to , but it won't because CO2 is only a tiny part of the problem that the media & politicans have become fixated with .