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[Zanzetkuken The Great]

...what would be the consequences to the climate of the planet and our civilization?

Minor thought that came to my mind and I believed would cause a bit of interesting discussion.

[Frumple]

Relatively certain a shift over the course of a week would kill pretty much every macroorganism on the planet. Ruddy thing's spinning too much, too fast, for that rapid of a deceleration and re-acceleration to not bugger everything right into the stratosphere,* possibly literally in some cases. Maybe over a course of a century or two it'd be survivable. Maybe not.

Nothing good, in any case.

E: If you're looking for some answers beyond the cataclysm, this site has some interesting broad-stroke responses.

*It would be roughly equivalent to a semi-truck slamming into a solid wall and then getting rocket-punched back in the opposite direction. Almost nothing of the truck would survive. Also that period in which we lost a substantial amount of our magnetic shielding (when the spin reached a near stop) would be radioactive hell. Hope everyone's underground getting crushed by tectonic upheavals then :V

[Loud Whispers]

Spoiler (click to show/hide)

[Dorsidwarf]

I'm pretty sure the big problems would be tectonic and magnetic. The earth rotates at something like a thousand miles an hour, and spread over a week (600,000 seconds plus change), that would be an average acceleration of a devastating 0.0033 meters per second per second.

Which would fuck up plate tectonics something nasty, but isn't going to detonate the equator or whatever.

[Frumple]

It's a bit over 1600 km/h, looking at it, not 1k km/s. Only about a half km per second. Doesn't really change that much, though :V

[Dorsidwarf]

I mistyped, corrected -.-

1600km/hr at equator
1000M/hr at equator

slowasfuck at poles

[SealyStar]

Based on those rotational velocity estimates, the equator would experience a practically negligible acceleration of

1600 km/h / (7 d * 24 h/d) = 9.524 km/h² = .000735 m/s²

So the "fly off into space" theory can be safely dismissed. Now, considering the effects on climate, orbits of various objects, etc., the world would probably be screwed anyway, but this bizarre situation would not instantly destroy the Earth.

[Zanzetkuken The Great]

I think the idea I had was that it would immediately start spinning in the opposite direction over the span of a week, then switch back.

No, I was talking about it occuring over the course of several days to a permanent shift.

Based on those rotational velocity estimates, the equator would experience a practically negligible acceleration of

1600 km/h / (7 d * 24 h/d) = 9.524 km/h² = .000735 m/s²

So the "fly off into space" theory can be safely dismissed. Now, considering the effects on climate, orbits of various objects, etc., the world would probably be screwed anyway, but this bizarre situation would not instantly destroy the Earth.

You forgot to include the earth speeding up to normal speed in the opposite direction in that calculation.  How fast would it need to be for everything to survive the transition period?

[Graknorke]

It depends on where the force is being applied from, doesn't it? If it's surface level in one place or all around the equator or on the entire surface at once or whatever else.

[Il Palazzo]

I agree that the question is ill-defined. We don't know what process makes the rotation reverse, so we can't know how it affects anything.

If, however, we were to handwave the process itself, and just look at the Earth spinning the other way around and what would be different, then there's two things that come into mind:

1. The Coriolis force would reverse, which would make the large-scale wind circulation go the other way around (i.e., the Westerlies would become 'Easterlies' and Trade winds would go the other way too).
Oceanic current circulation would be similarly affected.
How exactly the climate would change is hard to say, as it's a hugely complex interplay of air and water motion with geographical features. In broad strokes, I'd expect a complete mixup of rain patterns, with former deserts turning green and formerly green places drying up. Similarly, regions currently kept warm by oceanic currents could lose the natural heater, while other regions gain it. Lots of fires, starvation, flooding, lots of dying of animal, plant and fish populations - at least in some places.

2. In the long-term, reversed tidal interactions would make the Moon impact Earth, probably before the evolving Sun manages to do it in.

[Eagleon]

Depending on where the force is applied, over how much area (The equator? Just the crust? The crust and the mantle? The whole earth?) the results on tectonics would be very different, but keep in mind that the earth is 5.972 × 10^24 kg or 5,973,600,000,000,000,000,000,000 kg. The inertia involved with something that size is bound to be staggering. My gut tells me the plates would rip themselves apart before budging more than an inch. If it's simply applied to the whole body, all of that force would have to disperse into friction heat, no?

[Dorsidwarf]

Depending on where the force is applied, over how much area (The equator? Just the crust? The crust and the mantle? The whole earth?) the results on tectonics would be very different, but keep in mind that the earth is 5.972 × 10^24 kg or 5,973,600,000,000,000,000,000,000 kg. The inertia involved with something that size is bound to be staggering. My gut tells me the plates would rip themselves apart before budging more than an inch. If it's simply applied to the whole body, all of that force would have to disperse into friction heat, no?

This question is about if the earth magically reversed direction over a week, not about trying to reverse it.

[lemon10]

Yeah, a lot of people would probably die.

1) Firstly the effects of the earth slowing for and then reversing for a week on temperature and climate. It would probably form some freak tornadoes/hurricanes as a simple result of the change in direction. Much more important however is that parts of the earth would experience 3+ straight days of sunlight/night (as the earth would be turning very slowly in the middle, and then change directions, and go slowly in that direction). This would make some places have temperature so high/low that it would kill a very large percentage of the people there, the temperature in many places would almost certainly break the global temperature records by dozens of degrees. The high temperature regions would probably end up generating massive tornadoes/hurricanes as a result of the huge amount increase in temperature, and everything in the night zones would probably freeze solid. Things probably wouldn't be very bad in the in between areas, although freak weather could still be a real concern.
2) Secondly the long term effects on climate patterns. This would change the locations of agricultural areas, making large amounts of them into not-agricultural areas. This would probably cause huge job loss and have a huge amount of deaths from starvation (in the third world) in the medium term. Large amounts of areas would certainly change biomes, which would probably be another large problem.
3) Finally, the earths magnetic field. It is (thought to be) generated by the rotation of conductive materials due to convection currents. I'm not quite sure if changing the direction of the earths rotation would have any effect at all on it, if it would stop for a few hours in the middle of the rotation changing, or it would end up stopping it for decades. Even if it did stop, its apparently not sure what effects it would have (despite that it would seem like such an event would kill pretty much all larger life over time due to radiation and cancer, its thought to have happened before (every time that the poles reverse), and it didn't cause any significant effects on the fossil record).

[DJ]

What about gravity? Since Earth is spinning this fast, there must be a significant force pushing us outwards, and it'd disappear as the rotation speed reaches zero.

[Eagleon]

This question is about if the earth magically reversed direction over a week, not about trying to reverse it.

Yes, I know that. How magically though? Just the solid bits? Or is it magical enough to rotate the atmosphere? Because then you're just reversing all the weather patterns, all of the ocean currents, and the climate would 'just' be mirrored as closely as physical constraints allow. The more constraints you place on the question, the more interesting it becomes.