The Kardashev Scale is a logarithmic rating for a civilization's development or technology, used to hypothesize about alien civilizations or make predictions about our own future advancement.
Kurzgesagt
Cool Worlds
Isaac Arthur
Modified Kardashev Scale, based on Watts: In case the above formatting is broken: K = (log(W) - 7.38) / 9.73
Nuclear, solar -> only ways to Type I1
Heat dissipation becomes a huge issue for Type I civilization, inevitably.1 Regardless of the greenhouse effect, any planet increasing its energy use must get hotter.
Solar power on earth is limited by the Carnot Limit to ~68.7% efficiency.1 A more realistic limit is 30% efficiency.
The Kardashev Scale
Based on this, I propose population scales and a modified Kardashev Scale for local governments/systems/collections of systems. Of course.. that doesn't apply as well with FTL travel being commonplace.
Energy may not be the best measure, because efficiency is increased with technological progress.
Carl Sagan's Modified Kardashev Scale:
K0: 106 W
K1: 1016 W
K2: 1026 W
K3: 1036 W
Power levels should be measured as electricity, otherwise a 200-acre farm is a K0.2 civilization, a single person's survival needs make them a K0.3, and earth is already a K1.
Modifying Sagan's scale to represent population may be better: 1 = 1010, 2 = 1020, etc.
A person's needs can reasonably assumed to require a megawatt of power.
By the time a civilization even gets close to K2, they'll be so separated as to not realistically be one civilization.
Without FTL capability, you do not get to K3.
K2-3 civilizations can move galaxies with galactic Shkadov Thrusters.
K5 would be the observable universe being used as energy, and is only possible with FTL capability, multiversal access, or breaking laws of physics.