The connection between ideality and ecological footprint allows us to estimate how the IP index has changed historically and how it might in the future.
Based on my projections of ecological footprint, the IP index rose above a value of one by 1750, and doubled by 1820. It doubled again by 1900, and by the mid-1950s it had reached a value of eight. The index doubled to 16 by 1990 and is currently growing at close to its long-term rate of a little over one percent per year.
Because of its dependency on ecological footprint and the close correlation of footprint with energy production, it is very likely that the IP index will peak soon after oil production peaks. Based on my projections of energy production, the IP index will reach a maximum of about 23 to 24 by the mid-2020s, and then drop to zero between 2030 and 2100 (most likely by 2050).