Ed Oswald: While it might not play a role in our day-to-day weather, changes
in the Earth's rotation and orbit around the sun affect our long-term climate.
Did you know that the Sahara desert was once a rainforest?
Or that Greenland was once regularly ice-free?
This is the weather-wise podcast.
I'm your host ed Oswald.
And in this episode, we're going to explain how that was, and why that will be
possible again in the far distant future.
Stay tuned.
We have a great episode ahead.
We take the seasons for granted.
Winter becomes spring, spring turns to summer, and summer leads to fall.
These changes are a result of the Earth's orbit around the sun,
which happens every 365 days.
But what if I told you the Earth's orbit isn't constant?
It's true.
Over long timescales, our planet's orbit and tilt changes.
It's way too small to detect it in a human lifetime, but on geologic
timescales, there's a pattern.
These patterns are called the Milankovitch cycle Named after Serbian
scientist Milutin Milankovitch.
He was the first to theorize that the Earth's orbit on its axis and
around the sun changes over time.
Milankovitch's findings suggested earth's orbit changes in one to
three ways with progressively longer timescales, wobble, tilt, and orbital
shape, or in scientific terms, axial progression, obliquity, and eccentricity.
The shortest of these it's axial progression, or our planet's wobble.
Let's use a spinning top to illustrate this.
As it spins, the top wobbles in a circular pattern.
Planets do the same thing, just much slower.
Our planet takes 26,000 years to complete a rotation.
The next cycle is obliquity or the amount of tilt that
the earth rotates on its axis.
over 41,000 years, this tilt varies between 22.1 and 24.5 degrees.
This changes the amount of sunlight that the Earth's surface sees.
Using the spinning top analogy again, it's like somebody spun it at an angle.
But we'll have to ditch this analogy for the longest and final cycle, eccentricity.
Eccentricity is how circular an orbit is, with zero being a perfect circle.
Our orbit varies from almost circular to slightly more oval shaped and
then back to circular again for a hundred thousand year periods.
Now that we've explained these cycles, let's put these together in climate terms.
Planetary wobble affects how extreme the contrast between seasons are.
right now, seasons are more extreme in the Southern hemisphere.
around 13,000 years from now, the opposite occurs, and seasons become
more extreme in the Northern hemisphere.
The Earth's tilt may help moderate that, though.
When tilt is larger, more sunlight in summer reaches the
surface when it's tilted towards the sun, and less in winter.
Right now, the Earth's tilt is roughly at average science believe the Earth's tilt
is decreasing, however, which will make seasons milder over the next 10,000 years.
Orbital shape also plays a role in seasonal extremes.
Within nearly circular orbit, seasons are generally mild.
However, in about a hundred thousand years, the Earth's orbit will
be considerably more elliptical.
As a result, the earth receives 23% more sunlight at its closest approach,
causing extreme changes between seasons.
One thing is certain, however: Milankovitch cycles are not the
cause of current climate change.
Its cycles are too long to explain current changes.
However it is a driver of natural change, and one of the reasons why some parts of
earth planet change from less rainforests to deserts and a matter of few thousand
years, this happens in the Sahara desert.
The Earth's ice ages and their cyclical nature are also thought to be caused by
changes in the Earth's orbit as well.
There's even research supporting the hypothesis that a Milankovitch cycles
may have helped human evolution, too.
However, these cycles are most notable in long-term natural climate change.
They seem to explain some, but not all, of these cycles.
So, where is the earth headed climatologically over the next
one, 10, a hundred thousand years?
Scientists have several theories.
In general, seasons will moderate overall in the short term, and
the planet will continue to warm.
But this happens on such a long timescale, perhaps tens of thousands of years,
that our ecosystem will slowly adapt.
That isn't what's happening now, where climate change
happens in a matter of decades.
As we move further into the future, the Earth's tilt will lessen,
bringing more sunlight to the poles.
The rainforest will move northward as well, bringing deserts to life.
But at some point tens of thousands of years from now, these trends
will be overpowered by a much more elliptical orbit, which may
trigger the dawn of a new ice age.
Luckily humankind has a long time before that becomes possible..
The Milankovitch Cycles are only a part of our complex climate system.
However, understanding how Earth's rotation and orbit changes with time
Allows scientists to better understand our planet's cyclical climate patterns.
This was a pretty detail heavy episode, so we have plenty of links in our show notes
for you to read further on today's topic.
We'll certainly return to the subject of climate cycles again
in the future, but that's all the time we have for this episode.
We hope you learned something today.
Weather Whys is a production of The Weather Station Experts
and the Weather Whys company.
Today's episode was produced by Derek Oswald and myself from our studios
here in West Lawn Pennsylvania.
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