Few things bother me more than the absurd torturing of logic and reason required to label something "sustainable." I apologize to those educated readers who are aware of the 2nd law of Thermodynamics and already know why nothing is sustainable. But there's more to it than just an abstraction of perpetually increasing entropy. There are practical questions that the environmental movement chooses to ignore and cannot answer reasonably.
What exactly does sustainability mean? If solar output declines due to cloud cover (as often happens), then what percentage of that plant's output is sustainable? If a plant can produce 10MW in bright sun but only 800kW in thick clouds, is only 800kW sustainable? Clearly, 10MW is not sustainable through a passing cloud or at night.
And of course, solar panel efficiency degrades over time. Is something sustainable only above a certain energy efficiency level?
If an engineer defined "sustainability" is would be something like: "an energy source is sustainable if it can be expected to last more than 20 years and will over its lifetime produce greater than 100% of the energy it takes to produce, dispose and/or recycle." Of course the 20 year mark is arbitrary. But that's the point: every definition of "sustainable" is arbitrary.
Why are fossil fuels not sustainable? Humans have been harvesting coal for hundreds of years, oil and natural gas in meaningful amounts for well over a century. All the empirical evidence suggests that the fossil fuels can be sustained indefinitely. If a over a century of sustained use of an energy source doesn't demonstrate sustainability, then what is the standard of proof? Two hundred years of use?
Why are energy sources that receive massive amounts of government subsidy considered sustainable, but not those that receiver proportionally much less or none at all? Doesn't the presence necessity of subsidy inversely reflect the true sustainability of a source? If not, why not?
Is carbon emission the only applicable standard of sustainability? If not, what other measures are germane?
These are some of the questions that easily befuddle many environmentalists. But with enough thought, the smarter ones can be brought around to a realization: sustainability is not a scientific term. It is a political and economic term. It is political because of the power and money the issue attracts.
But more than anything else, it is an economic term. Something can be sustained as long as there is an economic incentive to do so. Whale oil as a lamp fuel would have been sustainable indefinitely. It's just that eventually enough whales were killed that it made the oil very costly to procure and made substitutes like kerosene far more appealing. The level of price at which whale oil would be sustained would be far too expensive for it to be useful. So it was not sustained-- but it could have been.
Likewise, Buffalo were hunted nearly to extinction in North America. But not totally. Why not? It simple: at some point, the scarcity made the value of buffalo much higher than the utility of killing more of them.
Absurd faith in carbon-scare computer models aside, there's no reason to think that fossil fuels will become any time soon more costly to use than they are worth. To the contrary, the world is "doubling down" with more fossil fuels being than ever before. Even as the world consumes more electricity than ever, electricity is overwhelmingly produced from fossil fuel sources.
There isn't any real debate. The issue is "settled" because people have voted globally with their feet. Fossil fuels are now and will remain for the foreseeable future the dominant and preferred energy source, and over time, this dominance has grown, not waned. They are getting cheaper, not more expensive. We are producing more, not less.
Let's stop pretending and just move on with optimizing the efficiency with which we consume those wonderful fossil fuels that are greening the planet and lifting millions out of poverty.