How about this for a Group 4 project?
‘To what extent does cooking contribute to global warming?’
The ideas I have had (and I am sure there will be more!) – cooking using yeast produces CO2, cooking using baking soda produces CO2, the energy needed to heat an oven will produce CO2, etc.
The project could be changed / adapted to the extent a family contributes to global warming, the extent the school contributes, the extent the country contributes, etc.
Good luck – it would be good to read your thoughts or ideas…..