Carl Sagan was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. Sagan assembled the first physical messages sent into space: the Pioneer plaque and the Voyager Golden Record, universal messages that could potentially be understood by any extraterrestrial intelligence that might find them.
Sagan advocated scientific skeptical inquiry and the scientific method, pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).
He suggested a change to Kardashev's original scale by interpolating and extrapolating the values given for types I (1016 W), II (1026 W) and III (1036 W), which would produce the formula K=(logP-6)/10 where K is a civilization's Kardashev rating and P is the power it uses, in watts. Humanity's civilization type as of 1973 was about 0.7, using an average power consumption of 10 terawatts (TW) as the value. See Kardashev scale for an in-depth discussion.
Sagan also proposed an Information Mastery alternative to the scale. He assigned the letter A to represent 106 unique bits of information and each successive letter to represent an order of magnitude increase, so that a level Z civilization would have 1031 bits. In this scale, 1973 Earth is a 0.7 H civilization, with access to 1013 bits of information. Sagan believed that no civilization has yet reached level Z, conjecturing that so much unique information would exceed that of all the intelligent species in a galactic supercluster and observing that the universe is not old enough to exchange information effectively over larger distances.
We believe this scale to be out of date, as we are already at Zettascale (1021) with 18 zettabytes of total global data in 2018 and predicted to reach 175 zettabytes by 2025, making us P and then Q already. The scale talks about "unique" data but that would be impossible to calculate.
Quote from Carl:
We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars.