Factual error: When New York is destroyed by the fireball, the Times Square giant TV (& other electrical items) is still on (although no picture - just static), but the super-flare would cause electrical items to overload before the main fireball hit, almost like an EMP.
Factual error: When John Kostler arrives in New York from Massachusetts, they pan out and show him crossing the Brooklyn Bridge. There is no logical way, on the route to Manhattan from New England, that one would cross this bridge. It would require him to travel completely out of the way, and judging by the competence of the protagonist, it becomes obvious this was used for visual effect only.
Factual error: Cell phone signals are repeatedly blocked by electromagnetic radiation from the sun. However, GPS devices, which receive a much fainter signal from satellites, continue to operate. For that matter, television broadcasting, which relies on satellite relays, continues until the end of the film.
Factual error: In the scene where Nic Cage sits at his computer and discovers what will destroy the world, he describes it as "A super-flare. A 100 microtesla wave of radiation that would destroy our ozone layer, killing every living organism on the planet." First, "tesla" is a measure of magnetism, not radiation, and 100 microtesla is a very weak magnetic field - an MRI machine uses around 3 Tesla. Second, destruction of the ozone layer would eventually kill all life on the planet, slowly, through radiation poisoning. It would not burn the planet to a cinder, as depicted in the movie.
Factual error: The 9/11 death toll of 2996 - which John Koestler notices on the sheet of numbers - is the overall total for that day's attacks. But it is next to New York's co-ordinates, and the other attack sites have their own entries with locations and death tolls.
Factual error: Almost at the end of the movie, when John is driving in a crowded street just before joining with his parents, there is a shot showing a Water Delivery Service Car fully charged which is not possible due to the emergency. It is supposed to be empty because of people taking water for themselves. (01:51:10)
Factual error: The aircraft that crashes in the movie is an Airbus A320-200, but however the wing strobe lights (white blinking lights on the end of the wings) are flashing in single phase (only flashing once a second), Airbus aircraft flash twice every second, only Boeing flicker once.
Factual error: The envelopes and letters from the time capsule are in pristine condition after 50 years underground. Even the papers are crisp and unfaded.
Answer: There is no intention on the part of the whisper people to warn humanity as a whole, merely a select group of children who appear, due to their telepathic powers, to be the next stage in human evolution, and their respective guardians.