As many other commenters have pointed out, it is possible for net global wealth to increase (e.g., the increase in total real GDP). As far as I understand, the main reason this is possible is the development of new "technology" -- in the very general, economic sense of the word technology [0], which includes anything that increases the productivity of a single worker; this can include everything from new technology in the traditional sense to new processes (e.g., agile vs. waterfall for software development, or more optimal supply chains) and investment in infrastructure (e.g., better road networks).
For example, a single farmer today can not only produce many times more crop compared to a farmer 100 years ago, but also safely and efficiently distribute this produce to consumers across the globe. In general, assuming everyone in the economy works equally hard, the total production (i.e., the global net wealth) can increase as long as technology is increasing.
[0] https://en.wikipedia.org/wiki/Production_function