You can read the full article where the chart comes from here:

http://www.coindesk.com/microscope-conclusions-costs-bitcoin/

"As can be conclusively seen, the relative impact of the bitcoin network does not even register on the radar of the fiat and gold-based monetary systems, representing a very conservative relative environmental impact of just over 0.13%, and a relative economic impact of just under 0.04%. When one considers Koomey’s Law, we can expect energy/GH to continue to half every 18 months until 2048.

This means that we can expect our current industry best efficiency of 0.733 W/GH to reach 0.0000000873804 W/GH. Thus – armchair academics take note – in the event that bitcoin scales to a million times its current size and market cap over the next 30 years, it’s environmental impact will still be insignificant compared to existing systems."