The ultimate size of the world’s economy is a function of the amount of available resources. The economy will grow as far as the resources allow. The resources are finite. Some of them are renewable, others are not. The economy is going to outgrow the renewable fraction of the resources (actually, it has done so already). The non-renewable resources are then used up. Once they are used up, the economy is too large for the available resource base. It will then collapse.
Economic growth is not the solution, its the problem.
There is no such thing as “sustainable growth”.