Remember, in Star Trek IV, a strange probe heads for Earth, sapping the power from Federation starships and scanning the oceans of Earth with a beam that pumps so much energy into the planet that it begins to boil the oceans, causing intense storms of hurricane force even in places that don't normally receive hurricane activity, such as San Fransisco. The Enterprise crew warps in a stolen Klingon warbird away... and disappear forever. The most experienced crew in Starfleet are now gone, the planet Earth, home to the Federation Council and homeworld of humanity, is now being ravished by a strange probe that can't be stopped.
Now, since the humpback whales aren't on Earth, the probe will continue to scan the oceans until it's satisfied, but by then the damage might be too much. Hurricanes cause tremendous damage, and given the amount of energy being used, might produce hurricanes of such power and ferocity that they exceed our current rating system by an order of magnitude. That much power being brought to bear against the coastal cities of the planet (which, mind you, hold most of the world's population even today), would cause tremendous loss of life and property damage. If the probe then leaves, the damage alone to the Federation would be devastating.
Most of the world's population would be suck in ruined cities washed out by flooding. If the damage was great enough, large areas such as the American midwest would be severely damaged, leading to crop failures as the rain washes out everything in its path. People in low lying areas will be flooded out and will only add to the refugees. The oceans would be deprived of almost all life, leaving the planet without a sustainable food source for those still alive. The Federation Council, what remains, will probably evacuate and set up an emergency government on another planet, such as Vulcan. With Earth in such a position, tremendous strain would be placed on the Federation economy trying to cope with a disaster of such magnitude.
The Klingons might choose that moment to strike in a similar way that several members of Starfleet advised attack following the explosion on Praxis. The Federation, faced with trying to rebuild and also launch a war, might have to sacrifice some relief efforts for Earth in order to concentrate on increased Klingon aggression, if not outright war. The entire Federation would probably be weaker, many humans would be angry at the destruction, and the loss of the Enterprise would no doubt be a blow to morale.
