What are Kardashev civilizations?

There are several ways we can measure the progress of human civilization. Population growth, the rise and fall of empires, our technological ability to reach for the stars. But one simple measure is to calculate the amount of energy humans use at any given time. As humanity has spread and advanced, our ability to harness energy is one of our most useful skills. If one assumes civilizations on other planets might possess similar skills, the energy consumption of a species is a good rough measure of its technological prowess. This is the idea behind the Kardashev Scale.

The Kardashev scale is a method of measuring a civilization's level of technological advancement based on the amount of energy it is able to use.

Kardashev Civilizations 

Image source: WIKIPEDIA

Russian astrophysicist Nikolai Kardashev proposed the scale in 1964. He categorized civilizations into three types: planetary, stellar, and galactic. A Type I species is able to harness energy on a scale equal to the amount stellar energy that reaches its home planet. Type II species can harness energy on the scale of its home star, and Type III can harness the energy of its home galaxy. The idea was further popularized by Carl Sagan, who suggested a continuous scale of measurement rather than simply three types.

Type I A civilization "close to the level presently attained on Earth, with energy consumption at ≈4×1019 erg/sec" (4×1012 watts). A Type I civilization is usually defined as one that can harness all the energy that reaches its home planet from its parent star (for Earth, this value is around 2×1017 watts), which is about four orders of magnitude higher than the amount presently attained on Earth, with energy consumption at ≈2×1013 watts as of 2020. The astronomer Guillermo A. Lemarchand defined Type I as a level near contemporary terrestrial civilization with an energy capability equivalent to the solar insolation on Earth, between 1016 and 1017 watts.

Their methods of energy production could be fusion power, using anti-matter and renewable energy using sunlight to produce electricity.

Type II A civilization capable of harnessing the energy radiated by its own star—for example, by means of the successful completion of a Dyson sphere or Matrioshka brain—with energy consumption at ≈4×1033 erg/sec. Lemarchand defined civilizations of this type as being capable of using and channeling the entire radiation output of its star. The energy use would then be comparable to the luminosity of the Sun, about 4×1033 erg/sec (4×1026 watts).

Methods of energy production: using hypothetical megastructures , as system of orbiting power satellites to enclose a star completely and capture most or all of its energy output,  feed a stellar mass into a blackhole, and collect photons emitted by the  accretion disc,   Star lifting is a process where an advanced civilization could remove a substantial portion of a star's matter in a controlled manner for other uses, using anti matter. 

Type III A civilization in possession of energy at the scale of its own galaxy, with energy consumption at ≈4×1044 erg/sec. Lemarchand defined civilizations of this type as having access to power comparable to the luminosity of the entire Milky Way galaxy, about 4×1044 erg/sec (4×1037 watts).

Methods of energy production: 

Type III civilizations might use the same techniques employed by a Type II civilization, but applied to all possible stars of one or more galaxies individually. They may also be able to tap into the energy released from the supermassive black holes believed to exist at the center of most galaxies.
White holes could theoretically provide large amounts of energy from collecting the matter propelling outwards. Capturing the energy of gamma-ray bursts is another theoretically possible power source for a highly advanced civilization. The emissions from quasars are comparable to small active galaxies and could provide a massive power source if collectible.

Kardashev thought  that a Type 4 civilization was impossible, so he did not go past Type 3. However, new types (0, IV, V, VI) have been proposed later.

So what type of civilization are we? Although humans use a tremendous amount of energy, it turns out we don't even qualify as Type I. About 10¹⁶ Watts of solar energy reaches Earth on average, and humanity currently uses about 10¹³ Watts. On Sagan sliding scale, that puts us currently at about 0.73. Not bad for a bunch of evolved primates, but it raises an interesting question. Could we even reach Type I? After all, we can't capture all the sunlight that reaches Earth and still have a habitable planet.

This question is studied in a paper recently posted to Arxiv. The paper looks at the three primary sources of energy: fossil fuels, nuclear, and renewable, and calculates their potential growth over time. On the one hand, reaching Type I would seem pretty easy. Make the production of energy your top priority, and you'll get there in the end. But each type of energy source has its limitations. In an extreme case, such as burning every ounce of fossil fuel we can, it could lead to a level of climate change that could end us all in a so-called Great Filter. You can't become a Type I civilization if you're extinct.

So the team takes a more nuanced approach, analyzing the physical limitations of each type of energy source, and balancing them against the need to limit climate change and pollution levels as outlined by the United Nations Framework Convention on Climate Change and the International Energy Agency. They found that even with realistic limitations, it is possible for humanity to reach a Type I level. The downside is that we won't reach that level until at least 2371.

That isn't necessarily a bad thing. The Kardashev Scale is a very blunt tool for measuring the scale of human technology. While advanced civilizations require significant energy, we have seen how advances in low-power computing and increased efficiency allow us to decrease or flatten our energy consumption while continuing to advance technologically. While this study shows how we could become a Type I civilization, it's possible that we'll be truly advanced when we realize we don't need to.

What is the Current status of human civilization? 

According to the astronomer Carl Sagan, humanity is currently going through a phase of technical adolescence, "typical of a civilization about to integrate the type I Kardashev scale." At the current time, humanity has not yet reached Type I civilization status.

Physicist and futurist Michio Kaku suggested that, if humans increase their energy consumption at an average rate of 3 percent each year, they may attain Type I status in 100–200 years, Type II status in a few thousand years, and Type III status in 100,000 to a million years.

Carl Sagan suggested defining intermediate values (not considered in Kardashev's original scale) by interpolating and extrapolating the values given above for types I (1016 W), II (1026 W) and III (1036 W), which would produce the formula

,

where value K is a civilization's Kardashev rating and P is the power it uses, in watts. Using this extrapolation, a "Type 0" civilization, not defined by Kardashev, would control about 1 MW of power, and humanity's civilization type as of 1973 was about 0.7 (apparently using 10 terawatt (TW) as the value for 1970s humanity). In 2019, the total world energy consumption was 581.51 exajoules (161,530 TWh), equivalent to an average power consumption of 18.44 TW or 0.73 on Sagan's interpolated Kardashev scale.

Sources: 

 Kardashev, Nikolai S. "Transmission of Information by Extraterrestrial Civilizations." Soviet Astronomy 8 (1964): 217. https://articles.adsabs.harvard.edu/pdf/1964SvA.....8..217K

Jonathan H. Jiang et al, Avoiding the Great Filter: Predicting the Timeline for Humanity to Reach Kardashev Type I Civilization. arXiv:2204.07070v1 [physics.soc-ph], arxiv.org/abs/2204.07070

https://en.wikipedia.org/wiki/Kardashev_scale