About the Global Index
Because the potential hivemining block rewards available to the entire network over a given time period are fixed, there is a maximum bee population that can be sustained by the network while still expecting all bees to be profitable (ie, to return more block rewards than the cost of the bees).
The Global Index gives beekeepers a simple way to make a value judgement call before creating bees.
When Global Index is below 100 (green is still visible in the GI pie chart), all live bees are expected to be profitable.
When Global Index is equal to or greater than 100 (only red is visible in the GI pie chart), there are more bees than can be expected to be profitable, and it may be wise to wait for the population to decrease before creating bees.