In the climactic moment of Richard Donner's 1978 Superman, the Man of Steel flies around the planet Earth so fast that he seemingly reverses the Earth's rotation in order to turn back time and save Lois Lane. It's his big selfish move, the one time he abuses his power for what he wants--even if he does end up saving Lois' life in the bargain. The decision looks even more selfish when you know what would happen if the Earth actually starting rotating on its axis in the other direction (we'll just ignore the ridiculous and impossible physics behind Supes' spin maneuver).
The Atlantic recently noted that a reverse spin would cause dramatic issues with our planetary climate. Quoting a BBC study by meteorologist Peter Gibbs, they explain that reverse rotation would do more than reverse the flow of everything across the planet. It would interfere with the Coriolis effect and trade winds, changing how weather moves across the world.
This river of high altitude, fast-moving air steers the mid-latitude depressions across the planet from west to east. Swirling masses of cloud and rain are pushed from Japan to the Pacific coast of America, and from Newfoundland to Cornwall. Reverse the flow and climate changes dramatically. The British Isles loses the moderating effect of weather from the Atlantic. A harsher continental climate becomes more likely, with a predominantly easterly flow bringing bitter Siberian winds in winter and hot, dry weather in summer.
Assuming this reversal happened a few hundred years back, it would have changed the entire history of human exploration and discovery:
Rotation complicates things. The flow breaks up into three separate cells known as the Hadley cell, the Ferrell cell and the Polar cell. Northward and southward-moving surface winds generated by the cells are then deflected to right or left by our old friend the Coriolis effect and we end up with the trade winds.
These constant easterly winds in the tropical regions were the motorways of the seas for sailing ships. A captain heading out of southern Spain could depend on picking up the northeast trades for a free ride to the Caribbean. Again, reverse the Earth's spin and the whole thing switches. Patterns of human discovery, subsequent empire-building and the resulting political geography would all be different.
The Atlantic adds that the Earth's magnetic field is actually produced by the Earth's liquid iron core as it spins. If the Earth's rotation wasn't reversed, but rather stopped entirely, we'd lose our magnetic field and absorb all kinds of harmful rays from the Sun.
Thanks for ruining the planet, Superman.