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How different would things be if Earth had always rotated in the opposite direction?

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Most of us don’t think about it much, but we’re all spinning really fast. The Earth is rotating us all from west to east at about 1600 kilometers an hour.

But what if it spun the other way? If this was a sudden change, we’d all probably die from being flung into the nearest wall at hundreds of kilometers an hour. Total bummer.

But if you look at what would happen if the Earth had always rotated fro east to west, the answer starts to get much more interesting. And yes, scientists have totally looked into this. The seasons wouldn’t change, since that’s based on how Earth’s tilted, but it turns out the climate would be very different in a way that would probably have changed the course of history.

Just like sunrise and sunset would reverse direction, the motion of stuff on the planet would, too. That includes both winds and ocean gyres, or loops of current. This is because of the Coriolis effect, where the path of something moving on another, spinning object will curve.

As it is right now, Earth’s spin causes winds and water flowing northward from the equator to take a big clockwise curve at least from our perspective here on Earth. For example, on our world the Gulf Stream Current carries warm water up to the northeast Atlantic, and the Jet Stream winds carry water, in the form of clouds, from Canada to the UK and Ireland. Flip things around, and suddenly western Europe gets significantly colder.

One study from 2008 found the UK and Scandinavia would have cooled by about 10 degrees - but also that the Mediterranean Sea becomes almost freshwater due to an enormous increase in rainfall in North Africa. At the European Geosciences Union’s 2018 General Assembly, researchers presented even more possible changes based on a computer simulation of Earth spinning backwards for 7000 years. What was once the Sahara and Middle Eastern desert became covered entirely in grasses and forests.

The Australian Outback wasn’t as dry, either. Earth’s major deserts got transferred to a significant chunk of what would have been the Amazon rainforest, part of northern China, and the southeast United States. With smaller areas of desert and more trees to act as carbon sinks, the simulation showed a global average temperature drop of about 0.2 degrees.

That might not sound like a lot, but it doesn’t take much for a global temperature change to have a significant effect on the climate. And finally, the reversed water current caused a significant drop in oxygen deep in the ocean. That led to a bloom of cyanobacteria, which is really algae, in the Indian Ocean.

They surged to a population basically never seen among algal blooms on our west-to-east rotating Earth. As for how 7,000 years of these climates would have changed history, it’s almost impossible to tell. But studies like these give us some idea of just how much of our history was driven by the simple fact that Earth rotates from west to east.

Thanks to Patreon patron Ennis Abel for asking this question! And thanks to all of our patrons for their support. We love looking into unexpectedly fascinating questions like this one, and we wouldn’t be able to do it without your help.

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