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I am writing a story where a freak magical accident causes a fully-formed landmass to pop into existence like it was there all along.

For the purposes of this question, let's assume:

  • the continent isn't very large, a bit smaller than Australia
  • the continent appears shortly southwest of Cape of Good Hope, obstructing the Benguela Current (image)
  • the continent magically replaces the water instead of displacing it
  • the continent has a mature ecosystem, with a east-west mountain range that would obstruct natural winds
  • the continent has an atmosphere & humidity level that matches its ecosystem
  • this happens in a climate that is prior to the Industrial Revolution (no greenhouse gases or ozone damage)
  • effects related to the crust & fault lines shall be handwaved

What would happen to local and global climates as the currents readjusted to the new landmass? Would there be unusual winds or storms forming; would the diverted water cause any flooding or tsunamis?

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    $\begingroup$ Nicely written question! $\endgroup$ – JDługosz Dec 31 '16 at 7:24
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    $\begingroup$ Damn, you cut off my answer about tidal waves caused by water displacement before I could make it. I don't know enough about climate science, but reading this XKCD what-if might give you some useful ideas: what-if.xkcd.com/10 $\endgroup$ – user45623 Dec 31 '16 at 8:45
  • $\begingroup$ If this "happens in a climate that is prior to the Industrial Revolution" does this mean it happens in the past prior to the Industrial Revolution? But when exactly is this? There can't be "no greenhouse gases" otherwise Earth would be frozen. Yes this is pedantic, but technical exactitude is a good thing. Greenhouse gases will be at pre-Industrial Revolution levels for whenever it is. A good challenging question. $\endgroup$ – a4android Dec 31 '16 at 11:37
  • $\begingroup$ @user45623 Sorry, but tidal waves aren't tidal. Their correct name, in English, is seismic sea-wave. Tsunami, adopted from the Japanese, seems to have become the accepted term. There might be more oceanographic effects in the short term than an impact on climate. That's the trouble with these complex systems issues, they're unpredictable. $\endgroup$ – a4android Dec 31 '16 at 11:41
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    $\begingroup$ Are you magically replacing the underlying geology or are you suddenly adding billions of tons of rock to an oceanic plate which will then sink into the mantle. becasue that will have many effects, like super volcanoes and global earthquakes. Mountains stick down into the mantle more than they stick up in the air. $\endgroup$ – John Jan 1 '17 at 8:18
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I'm afraid that the answer to your question is too broad. Climate models are complicated, even without people who deny the science, and the second-order effects will be unpredictable.

  • Will there be lot of snow? Will it last longer than ocean ice in the same location, increasing albedo?
  • Will the gaps be wide enough so that currents pass through them?
  • Will there be upwelling of nutrient-water, or will upwellings be obstructed? What does that to the ecosystem in the oceans?

That being said, no tsunamis. If there is no splash dropping the continent, the currents will create slow flooding rather than a fast wave.

The side of the continent facing the current might get some swamping, and so might other coastlines, but that won't be worse than a normal storm surge, just without the storm.

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  • $\begingroup$ So, what you're basically saying is other than the obvious "where did this continent come from" reaction, it would just throw the local ecosystems out of whack for a few years? I might want to consider having the water get displaced in that case... $\endgroup$ – user10933 Dec 31 '16 at 17:54
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    $\begingroup$ @phoenixwarbird, it might have huge consequences, but we can't tell which ones. Global warming, global cooling, complete breakdown of ocean ecosystems, or perhaps not quite as catastrophic. $\endgroup$ – o.m. Dec 31 '16 at 21:08
  • $\begingroup$ looks like I'll be coming up with my own solution then. Thanks for the ideas! $\endgroup$ – user10933 Dec 31 '16 at 21:54
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The major effect of a new Australia south-west of the Cape between 30° and 60° southern latitude would be the obstruction and disruption of the ring of permanent westerly winds which produce the Antarctic Circumpolar Current. Breaking this ring of permanent winds would lead to the loss of the thermal insulation of the Antarctic; the climate of the Antarctic would gradually warm up tending to become somewhat more similar to the climate of the Arctic, at least near the coast. (The Antarctic would remain much colder than the Arctic because it's a continent and not an ocean.) In time--quite a long time--part of the ice will melt, rising the sea level (possibly considerably), and maybe making possible some human occupation of part of the Antarctic.

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    $\begingroup$ There is a pretty big gap between South African and Antarctica (4000 km), enough to fit an Australia in (3000 km, north to south in the eastern part). Since there is already an ~1000 km gap in the southern circumpolar (ie between South American and the Antarctic Peninsula), I doubt the flow resistance of a second gap the same size would be significant enough to do the things you suggest. $\endgroup$ – kingledion Dec 31 '16 at 15:56
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    $\begingroup$ @kingledion: Two 500km straits are not equal to one of 1000 km; and while the Drake passage lies between two narrow peninsulas, this new continent would be much much wider. It's not about the flow of water, it's about breaking the circle of winds. At things are in the real world, there is one permanent continuous wind circling the Antarctic west to east, which insulates the Antarctic from the rest of the atmosphere. With this permanent wind broken down, the air would eventually mix with interesting and unforseen consequences, not only for the Antarctic but for South Africa as well. $\endgroup$ – AlexP Dec 31 '16 at 17:21

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