Break the humans and their toys, not the laws of nature
Do not even bother with trying to change the laws of nature because — as the religious like to point out — they are so intricately woven into each other that any such change pretty much wrecks the universe as a whole.
Instead: break the humans, that is a lot easier. And there is a very simple way to achieve that which you are after:
Make humans unable to read
A virus of some sort knocks out the part of our brain that makes us able to comprehend written language. That part is quite localized and we can lose this without otherwise becoming mentally disabled. This makes us unable to communicate in written form and makes us unable to take in stored information. Bye bye Wikipedia, all school books, anything and everything expressed with letters are suddenly unavailable to us.
But we can still talk over long distance. That will need to be remedied...
Wreck the computers
At the same time as they release this bio-engineered virus, the Rousseauists (*) — as the terrorists / freedom fighters call themselves — detonate a number of stolen nuclear weapons in orbit above significant population centers. The resulting High Altitude Electromagnetic Pulses destroys much of the electronics in the world. Every processor, diode and transistor in sight of the explosions will be fried.
Without being able to communicate in written form, humans will be unable to make any machines or electronics to replace the ones that were destroyed. Knowledge transfer will be oral only. The few remaining working machines will be very valuable (plot hook right there).
Of course there will be quite a few ecological disasters here and there... as oil tankers run around, chemical processing plants break down and/or go up in flames, the odd nuclear power plant meltdown, the inability to combat forest fires, huge dams collapse (if you cannot control the water flow, eventually the dams will collapse) and so on.
Plus the fact that all forms of non-fossil energy generation stops working instantly, because the power grid has just been destroyed; power switching requires electronics. Which in turn means that global warming becomes definitively unstoppable.
On the plus side, there will not be as many humans left to cause global warming either because as the food distribution chains break down, the availability of fresh water and sanitation becomes abysmal, and health-care ceases to function we can expect mass epidemics and starvation to the point where mankind becomes next to extinct.
So there you have it... you have made humans go back to nature. Happy about the result? :)
(*) Jean-Jacques Rousseau is the source of the catch-phrase / philosophy "Back to nature".