How would a planet have alternating "hot" and "cold" years?

[ScaryMJDiamcreep]

I'm wanting my world to alternate between being "hot" and being "cold" on a yearly or bi-yearly basis. This planet is the same size as earth, has a day the same length as earth, an orbit of 364 days, and a moon of the same size as earth's moon that has an orbit of exactly 28 days.

The current methods that I've thought of involve the planet either residing in a binary star system where the stars orbit each other in such a way that one year for the planet it will see both stars, then the next it'll only see the one, or it has a large moon or a planet orbiting it at an orbit of 4 years, such that it'll be in the way of the sun one year, making a "cold" year, then be to the side, making a medium year, then behind the planet, making a "hot" year, then to the side again, then in front again.

The second method seems implausible, and I'm not sure how the first method would work, so any feedback or other methods would be appreciated.

Note: the difference between the same time of year on a "hot" year and a "cold" year is only between 5 and 10 degrees Celsius.

 

[CupofJoe]

Does it have to be global? Or could just a region be enough? If it is regional, then you could look at El Niño and La Niña weather/climate events.

 

[ScaryMJDiamcreep]

I'd prefer it to be global, and I forgot to mention that the planet has seasons as normal, so I can't go for seasons to cause the change.

 

[Night Gardener]

If you don't want to mess with interplanetary configurations, the explanation could be biologic.

Have an organism, I'm thinking plants and trees, that emit out greenhouse gases every other year as part of their reproductive cycle. Have a binary or symbiotic organism that lives with this predictable cycle, and thrives/absorbs the excess green house gases over a year.

You'd get your "hot" climate, and "cooler by comparison" climate. Without radically effecting the light available to earth...

Also, with a myriad of other adjustments if you do change the sunlight availability: if you do tinker with sunshine interacting with the earth, your vegetative life will probably include red and purple chlorophyll pigments to capture that range of light spectrum in their photosynthesis to survive in radically different growing conditions available every other year or so. They may also produce 'bloom' on the leaves (appears blue to the human eye) to help capture even more light spectrum. White or yellow pigments are usually the results of selective breeding by humans, aka 'variegation' is typically an otherwise benign virus introduced to a plant population.

So, descriptively speaking, a big majority of leaves may appear tri-colored, mottled, or indeed change pigments over a growing season. Like autumn leaves, they might shed 1 color and produce new growth in a new color according to the warm/cool years, also in the time of the regular 4 seasons.

People could anticipate how warm or cool the upcoming year might be based on the colors emerging from new growth on deciduous trees in the spring...

 

[Steerpike]

First thing I thought when I saw the thread title was a binary system. Maybe one star is much further away, but enough to that it really elongates the orbit of the planet so that one full year passes far away from the main sun, while the next full year passes much closer to the main sun.

 

[ScaryMJDiamcreep]

With the binary system thing, I'm mostly imagining either two identical stars, where the planet has a cold year when it's only getting light from the one star, and a hot year when getting light from both, or having one star be smaller and colder than the other and the cold year being when the planet is on the side of the colder star. I'm just not sure whether either approach would work as I'm imagining it. Especially as far as which way round the hot and cold years would be for the first system.

 

[K.S. Crooks]

I had the same thought as ScaryMJDiamcree. Another option is to have your "planet" be a moon and be in its planet's shadow some of the time or even be part of a dual planet that orbit each other and as such block each other from receiving enough light.

 

[SoulThief]

Besides distance from sun, two other things to factor in are tilt and landmass distribution across the planet's surface. Tilt is fairly obvious and you could play with that changing/wobbling. Landmass is an interesting consideration. Land generally heats to a higher temperature than the ocean, meaning that the northern hemisphere on average has a hotter summer than the southern despite the northern hemisphere being further away from the sun in its summer.

So, with one sun, you could have a planet whose tilt "wobbles" and figure out a distribution of land/sea that pushes temperatures to extremes.

 

[ScaryMJDiamcreep]

Messing with the tilt messes with seasons, and with landmass, that wouldn't cause it to swap from being hot and cold on a yearly or bi-yearly basis.

Also, the difference in average temperature between a "hot" and a "cold" year is about the same as the difference between the average in America and the average in the UK, with winter on a "hot" year being similar to the UK(is there gonna be snow? we just don't know) and winter on a "cold" year being more like America(how deep is the snow gonna be this year?), and vice versa for summer(In the UK, our summers are nothing in comparison to American summers).