This article contains spoilers for Action Comics #1029/
Superman is dying in the comics - and the reason is a mystery. Phillip Johnson's Action Comics run promises to transform the Superman franchise in a disturbing way, with Jonathan Kent forced to confront the reality that his father is fallible - and won't be there forever. Having served as a member of the Legion of Superheroes in the distant future, Superboy has returned to the present day aware of his father's fate.
Action Comics #1029 - from Phillip Kennedy Johnson and Phil Hester - sees Superman and Superboy work to close a portal in space before dangerous aliens can overwhelm them and invade the Earth. "This breach that's opened up," Jonathan tells his father, "This fight that we're fighting right now? In the future, this is one of the last documented incidents that you're a part of on Earth!" Although Jonathan averts what he fears will be his father's death, Superman still takes a beating during the confrontation and he's lefy with broken bones and internal bleeding. The final scenes see Darkseid watching Earth with fascination, told by his agents that Superboy's words are true; the Man of Steel is indeed dying. But what exactly is going on?
The most likely scenario is that Superman's powers are misfiring somehow, making him weaker. Superman is essentially a living solar battery, absorbing the energy of the sun and metabolizing it in order to grant him his powers. But his cells are capable of absorbing other energy as well; that's why Kryptonite is so dangerous since his body metabolizes the radiation emitted by those alien chunks of rock. It's possible Earth is being bombarded with some other form of energy, perhaps interdimensional in nature, and that Superman's cells are prioritizing absorbing that rather than the life-giving power of the sun. The longer this lasts, the more his body is bereft of solar energy, the weaker he gets.
This theory would account for everything seen so far in Action Comics #1029, but it raises a disturbing question; why isn't this mysterious energy being absorbed by Jonathan Kent as well? Again the issue doesn't answer this question, but educated guesses can be made. Superboy's history is a complex one, involving a number of temporal and interdimensional warps, and it's quite possible those experiences have altered his Kryptonite physiology a little. If an energy is permeating into this dimension from another, Superboy could well be immune.
And that means the world shouldn't write Superman out just yet. Clark Kent may be weaker than before, but Jonathan Kent knows something is going on; he's forewarned by his future knowledge that Superman's days are numbered, and he's willing to go to any lengths to prevent his father's death.