To use a variant of Roko's Basilisk (and you have been duly warned).

Suppose that the year is 4xx BCE or so, and you are in Athens. (Also, this is slightly fanciful, but suppose that everybody to-be-named lived at the correct times.) But you're otherwise you. In fact, you're you, but armed with fluency in ancient Greek and also a copy of Wikipedia, a copy of Wikihow, a complete DVD set of Mythbusters, and that one rad poster that the guy down the hall had in his dorm about time travel [0]. You're ready to rock, and you quickly convince the Athenians that you can and will help them use modern technology in order to win the upcoming wars. All you want in return is to go along for the ride, but you insist that no matter what, there will be some reforms to the politics of the region: slavery will be banned and all will be given the vote.

(1) You and Pericles optimize, fertilize, and mechanize. You win the wars. The finances of Greece swell. You balance the books and advance trade. You begin to tap into the natural resources of your surroundings, into iron and coal and steel. You win all of the wars. The Greeks roll across Europe rapidly. You pass away. Skipping feudalism, your children strike oil and go directly to a planned economy, using future understanding of psychology and memetics to ease the rapid industrialization. At some point, somebody builds a nuclear weapon. There is a USA vs. China vs. Greece cold war. You don't personally live to see it, but technology proceeds at roughly the same pace, until the present-day technologies emerge.

(2) Or do you? After all, you've seen the future. You've been from the future. You know what will happen if fossil fuels are tapped into. But you also know that you can't unknow the existence and potential of that oil, of the potential of plastics. You know that you have an ethical obligation to prevent the world from using oil irresponsibly. So you explain all of this to the Athenians, and you convince them of these ethical conclusions.

They agree: Oil is powerful. Too powerful to be used without a central committee's planning and approval. You make the mistake of giving Plato access to Wikipedia, and he learns about the United Nations. A plan is hatched: Athens shall form an Athenian League of Nations, and shall convince all other nations to join in responsible use of oil and other natural resources, for the good of all people. But Plato is not unpragmatic, and so Athens shall achieve military and technological superiority first, and use both the pen and the sword.

Y'know what? It's not bad. Basic improvements to hygiene, cooking, and agriculture lead to control of Greece. Computers are built out of wood, stone, and water. Greek bauxite is converted to aluminium. A robust understanding of chemistry and economics (and a fortunate lack of economists!) leads to a low-waste, sustainable, environmentalist culture. Your first attempts to convert the non-Greeks end in violence and war, but as your reputation spreads, Greek society attains a mythic status: technologically advanced, politically opinionated, and militarily invincible. As nations peacefully negotiate with the League, your sons and Aristotle use neocolonial techniques to wield diplomatic and economic power over them. Access to oil, as ensured by the convent of You, Adam & Jamie, is carefully metered. There are plastics, rubber, and paper. When the last few holdout nations are cornered, they lash out unsuccessfully against an overwhelming coalition. Your grandchildren preside over ALoN's sustainability council, a unilateral peacekeeping and resource-managing force.

(3) Ha! Just kidding. They read the rest of Wikipedia too. And remember, everybody gets to vote, including the uneducated. The resulting arguments are heavily biased in favor of the existing oligarchs and landowners, who do manage to ostracize a few of each other before Pericles secures his gilded-fist control. Athens becomes the first futuro-fascist nation-state ever, unifying under a single banner of making Greece greater than it ever willen was. You do get computers and aluminium produced, but the computers are used for bureaucracy and the aluminium goes to the war effort. By the time Greece is unified, world domination is already being planned, and while you don't live to see it, over the next three generations, large waves of industrialization advance the state of the art of war. Athens builds a nuclear weapon. They build several, in fact, and start using them. By the time the war machine collapses, most of Europe is uninhabitable and the climate is altered for the worse.

Story over. So, as we know, the Athenians didn't know any of this, and the following series of wars led eventually (skipping over a lot) to the Romans winning. And then eventually the Romans stopped winning. In fact, that's the pattern throughout history of every large empire. Meanwhile, environmentalism is a relatively new concept, both in terms of what we know about how to help take care of Earth, and also political and social acceptance of our obligation to do so. We shouldn't put a burden on ourselves to know the future and then completely change our government to match that expected future; how can we be so certain, when we don't have a time traveler showing us what the future will be like?

[0] https://topatoco.com/products/qw-cheatsheet-print