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If an alternate Earth had an axial tilt of 45 degrees, what would the seasons look like? Being the most extreme tilt a planet can have before simply replacing North/South with East/West, obviously such a world would have rather extreme seasons, what just how extreme? What would these extreme seasons look like? What would their effect be on the ecosystem?

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    $\begingroup$ At each solstice, a quarter of the world is going to be in darkness. I'd say that winter and summer are going to be pretty nasty here past 45 degrees N/S, because you could potentially spend several months in effectively 24-hour daylight or darkness just in, say, Canada or Russia. Even the northern U.S would have several days to a week or two in such conditions. Wildlife outside about 20 degrees N/S is going to need to adapt to wild temperature swings over a year: expect a lot more warm-blooded creatures, namely mammals (likely with fur), that can survive snowy winters and hot summers alike. $\endgroup$ – Palarran Nov 24 '16 at 16:39
  • $\begingroup$ @Palarran Forget wildlife, what about plants? Can you have plants that can survive 3 months of freezing and 3 months of extreme heat? Without plants, no animals anyway. $\endgroup$ – Feyre Nov 24 '16 at 16:42
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    $\begingroup$ The most extreme tilt is not 45 degrees, it's 90. Tilt describes how far off perpendicular the rotational axis is. If it's at 90, the day/night cycle will not be tied to the planets rotation but to the rotation of the planet around the star. $\endgroup$ – Nathaniel Ford Nov 25 '16 at 0:22
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    $\begingroup$ @Feyre: There's plants that utilize the rare rains in the desert by growing, blooming, and producing seeds rapidly. A cactus-like survival mechanism could also be adapted to this kind of climate, and ditto for plants that store most of their energy underground in thick roots. So I'd imagine that plants would adapt to grow either in the heat or in the temperate climate in the spring/summer, and hibernate or die off during the seasons that are wrong for them. So you might see a very barren winter, heavy plant growth in the spring and autumn, and a bit in the summer. $\endgroup$ – Syndic Nov 25 '16 at 13:50
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I'd imagine the 4 seasons area would have harsher degrees of winter, and get a glimpse of tropical summer.

On details that would make the dry land parts of earth are already smaller than we would naturally have (without global warming), cause the earth's pole area that didn't catch direct sunlight throughout the year are smaller.

At the ecosystem level, there may be a smaller pure tropical climate (or maybe there isn;t any at all), and most creatures are experiencing highly fluctuating seasons change. If this happens naturally from the very beginning, I expect a thick furry creatures like polar bear may developed a shedding cycle as part of their survival process in the summer, while others who don't developed a habit to survive.

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Winter would be colder and summer would be hotter.

Overall there would be a greater gradient of temperature from the southern hemisphere to the northern hemisphere. That would result in stronger wind and sea currents.

How that would affect the environment and ecosystems is difficult to tell because there are many feedback effects involved. I would naively say that there would be way more hurricanes and tornadoes, thus making life more difficult in general.

Another effect would be that the Earth's magnetic field might deflect less solar radiation because it would be too inclined. There might be a higher level of radiation on the surface of such a planet.

However the odds of a 45 degree axial tilt planet are very small. Because planets are formed by accretion of dust around a massive sun, most debris are in the same accretion disk. Planets are tilted because in the late stage of accretion, a planet in formation is hit by another smaller planet (usually moon sized) at a certain angle, tilting the planet. However because most rocks are in the same accretion disk, for a planet to tilt to 45 degrees, you would need a planet of similar size to hit it from a large angle to cause such a tilt. Statistically the odds are small. That s why you don t see many planets with such a tilt in the universe.

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