Quoting Wikipedia: More recently, the law of unintended consequences has come to be used as an adage or idiomatic warning that an intervention in a complex system tends to create unanticipated and often undesirable outcomes.
The Industrial Revolution and Climate Change are as good example as you can get of an unintended consequence. I cannot imagine that the hundreds of inventors and entrepreneurs active in the early days of the Industrial Revolution thought that they might be beginning the process which would bring the human species to the edge of extinction or beyond. They could only see the perceived benefits of industrialisation even when scientists were suggesting (not warning) that industrial activity could have an effect on the earth's climate.
The problem that humankind faces now is that it is blinded by its own intelligence, an intelligence which leads to the conceit that, "we can do anything if we try". The same intelligence which enabled the Industrial Revolution is now being deployed to find an answer to the consequences of the same revolution. However, no consideration is being given to whether or not industrialised humanity is the core threat to both the earth (as it was before1790) and humankind itself.
Quoting from Owlcation: The Industrial Revolution was the most important thing to happen in human history since the time when animals and plants were domesticated. Before the Industrial Revolution happened, each generation of people produced a roughly similar amount of products to their predecessors and overall economic wealth was fairly stagnant. After industrialisation, production began to grow quickly and generally continued to grow.
Its fair to imply from this that, prior to industrialisation, global population was relatively static and exploded after industrialisation and the graph below gives an idea of the impact.
The problem that we face today is somewhat more intractable than is suggested by Greta Thunberg and Extinction Rebellion. Today, the problem is that global population is unsustainable, even if we all become vegetarian and use electric bikes. There are some signs of change, the 'birthstrike' movement is one such but I doubt that humankind has the ability, in general, to pull back from its own demise. In nature, populations of most species are regulated by the impact of food availability, weather and predation but that isn't the case with us. Our only real enemy is ourselves and I hope that Greta Thunberg will consider that she is as much a part of the problem as anyone else.