
Every 202,500 Years, Earth Wanders in a New Direction - montrose
https://www.nytimes.com/2018/05/21/science/earth-orbit-change.html
======
mkempe
The change in orbital shape was already known as one of the Milankovitch
cycles [1]. This study seems to give us the most precise measurement.

In the context of climate change, when Earth's orbit becomes more eccentric
(our path over the next 200k years) seasonal changes increase in magnitude.

[1]
[https://en.wikipedia.org/wiki/Milankovitch_cycles#Orbital_sh...](https://en.wikipedia.org/wiki/Milankovitch_cycles#Orbital_shape_\(eccentricity\))

~~~
patall
> In the context of climate change, when Earth's orbit becomes more eccentric
> (our path over the next 200k years) seasonal changes increase in magnitude.

Isn't that only so on one of the hemispheres? Right now, earth is slightly
further away from the sun when its summer on the northern hemisphere which
means that our summers are some 5-7 days longer than our winters and our
seasons are actually less intense here.

~~~
madaxe_again
It’s more complex than either case. The eccentricity of earth’s orbit
precesses, as well as earth’s axial tilt.

In a circular orbit, the seasonal variation is driven solely by the axial tilt
and relative hemispherical insolation bought about by earth’s own shadow, and
angle of the sun to terrain.

With a variable distance from the sun, the seasons become erratic, as these
two variables precess out of sync - you end up with winters in one hemisphere
where the earth is close to the sun, making for mild winter and scorching
summer in the other hemisphere. Equally you end up with the earth far from the
sun, and bitter winters and cool summers. Finally, you have the precessions
180 degrees out of sync, and you end up with almost no seasonal variation.

So - it makes the overall swings far more extreme, but in some phases can
result in milder seasons.

~~~
Unkechaug
Where are we now and where are we headed?

~~~
milankovic
The simple truth is: No one really knows.

How do you determine the exact position in a cycle of 400000 years?

------
geuis
Better article with more details and a link to the relevant paper
[https://www.universetoday.com/139198/jupiter-and-venus-
chang...](https://www.universetoday.com/139198/jupiter-and-venus-change-
earths-orbit-every-405000-years/)

~~~
ChuckMcM
I expect this is the danger quote _" “The climate cycles are directly related
to how Earth orbits the sun and slight variations in sunlight reaching Earth
lead to climate and ecological changes,” said Kent, who studies Earth’s
magnetic field. “The Earth’s orbit changes from close to perfectly circular to
about 5 percent elongated especially every 405,000 years.”_ which comes from
here ([https://news.rutgers.edu/earth%E2%80%99s-orbital-changes-
hav...](https://news.rutgers.edu/earth%E2%80%99s-orbital-changes-have-
influenced-climate-life-forms-least-215-million-years/20180502#.WvSKMiBlDIX))

------
gwbas1c
Based on where we are in the Milankovitch cycle, should we be getting warmer
or colder?

(I keep checking the comments of this article hoping that someone knowledgable
can explain how this impacts the climate.)

~~~
noiv
NASA to the rescue:
[https://earthobservatory.nasa.gov/Features/Milankovitch/](https://earthobservatory.nasa.gov/Features/Milankovitch/)

Basically it's not measurable within a lifetime and the signal of human
interaction with the climate is magnitudes higher.

~~~
mkempe
It is extravagant and ludicrous to claim that the signal of human influence
(CO2 ppm?) on the climate is _magnitudes higher_ than that of the Milankovitch
cycles -- which have been driving the regular glaciations and interglacials
over the last 3 million years.

~~~
lstroud
That said, we do use ice cores from periods that would cross multiple of these
cycles. If these cycles change how we estimate those values, then the
statistical models we’ve built based on them will need to adjust accordingly.
So, it’s not that it doesn’t have an impact, just that the impact probably
doesn’t change the trend line.

------
palisade
I made a thing. To wrap my head around the Milankovitch cycles.
[https://i.imgur.com/V3RIKL5.png](https://i.imgur.com/V3RIKL5.png)

------
everdev
TLDR; Scientists believe the Earth's orbit oscillates between circular and
more elliptical due to the gravitational pull from Jupiter (big) and Venus
(close). It takes 405k years to complete a cycle.

~~~
milankovic
Exactly, but what is new here? The duration of the complete cycle?

Well, that number is new, to me at least, but the principle was well known
before, I assume?

I don't get it.. don't they teach basic astronomy in schools anymore?

~~~
flyGuyOnTheSly
>don't they teach basic astronomy in schools anymore?

Not in Ontario, Canada, they don't...

I had to get accepted into a university and then apply for first year
astronomy to get any basic astronomy instruction whatsoever.

~~~
milankovic
Wait.. are you serious?

Guess I should consider myself lucky that I had a physics teacher who taught
us about the thing that we stand on and live on, what it is, where it is,
what's around and how our solar system works.

Ha, I am really shocked now. Honestly, I can't believe this. I should probably
not dare to ask someone on HN if they ever heard about the Milk Way or
something.

~~~
recursive
Or at least don't do it in such a dismissive way.

------
early
Paywall articles should be banned here

------
zw123456
The result of which is ... ?

Does this lead to some occurrence such as a mass extinction or something of
that nature?

Seems interesting.

~~~
cryptonector
At times of higher eccentricity you get more pronounced differences between
summer and winter. If this coincides with a glacial period (and it has) that
probably means that the glacial period sets in faster / is colder than when
the orbital eccentricity is low -- but it also means that interglacials set in
faster and are warmer.

~~~
thaumasiotes
> At times of higher eccentricity you get more pronounced differences between
> summer and winter.

Why would this be the case?

~~~
cryptonector
Because eventually perigee coincides with summer or winter in either the
Northern or Southern hemisphere (and then the apogee will coincide with the
other hemisphere's opposite season, naturally), so one of them will get more
sunlight (heat). BUT! The Northern hemisphere has much more landmass than the
Southern one, which accentuates the differences between seasons because land
heats up faster in the summer and cools down faster than the oceans in the
winter, and also land provides a platform for ice accumulation. This is the
reason that glacial periods involve much more ice in the Northern hemisphere
than in the Southern hemisphere.

It is generally believed that glacial periods set in when the Northern summer
coincides with the furthest point from the Sun on Earth's orbit, while
interglacials set in when the Northern summer coincides with the point of
closest approach to the Sun. Summer is the key because once ice lasts past the
summer then summer cannot heat up the Northern hemisphere as much as usual:
ice reflects a lot of the Sun's energy. Conversely, if the summer is warm
enough to melt more snow and ice than was accumulated during winter, then you
can't have a glacial period.

It is important to note that there are other orbital cycles that matter here,
especially the precession of the equinoxes, which is the cycle that relates
which hemisphere gets its summer closest to the Sun. Earth's axis of rotation
itself rotates, very very slowly. The precession of the equinoxes is a 25ky
cycle.

Another cycle is the angle of the Earth's axis of rotation to the ecliptic.
This varies a fair bit over the years, and this one is (IIRC) the most chaotic
of the orbital cycles.

All of these cycles, known as the Mylankovitch cycles[0], have winter/summer
difference accentuation/attenuation effects. The Mylankovitch cycle theory is
that when these coincide in certain ways you get glacial or interglacial
periods.

[0]
[https://en.wikipedia.org/wiki/Milankovitch_cycles](https://en.wikipedia.org/wiki/Milankovitch_cycles)

