What is the World Economy?

Economists frequently talk about the World Economy and it's growth but in a world of fixed resources, what growth is being measured?

In a world of fixed resources, output should be balanced, that is, if the GDP of one country is increasing, the GDP of another country should be decreasing and in that sense we can talk of economic growth since one country will be using resources more efficiently than another and attracting the scarce resources available away from that other country. But to what is the world economy compared when it is said to grow by 2%? What is the change in resources that has happened to cause that 2% growth? Is it that we have removed natural resources from the ground faster than the year before and therefore increased output? If so, then at some point in the future, the resources should be removed less quickly and growth should be negative to achieve balance in a world of fixed resources.

Perhaps it might be better to talk of "wealth" when measuring global increases in productivity and outputs since the essence of progress is to ensure that everyone is better off than at some previous point in time. Global output growth of 2% does not tell us much about our progress as a race.