By Anna Cutmore
Communicating science is really quite difficult. We can all relate – someone starts talking about an unknown, highly technical subject, and within seconds you’re contemplating what you’re going to have for dinner.
I think that’s where the problem arises with understanding climate change. So many people assume it’s complicated, dull and confusing – completely understandable, because it certainly can be.
But it doesn’t have to be!
A key confusion surrounds the difference between natural and man-made climate change (aka global warming). The former has been taking place for millions of years, with the latter occurring only over the past couple of hundred years, due to our love affair with burning fossil fuels.
Now, I’m sure you’ve heard of man-made global warming. But here I want to explain a fundamental cause of natural climate change, to make it easier to understand the difference between the two.
Let me start by asking two easy questions… hopefully, you’ll answer “yes, I’m interested” and I can explain one of the most incredible discoveries ever made in climate science…
My two questions are:
- Are you interested in Ice Ages?
- Are you interested in outer space?
- Obliquity
- Precession
- Eccentricity
Woolly mammoths, ice sheets – the Pixar film that made one too many sequels…
Ice Age 2002 Poster (left); Awe inspiring image of outer space (Right)
Image credit: Blue Sky Studios/ NASA
Pictures illustrating the enormity of our sun, Jupiter’s many moons and whether life exists beyond our galaxy…
Yes to both? Good.
Wondering how they tie in with each other?
Well, the link is pretty fascinating.
It’s all down to how our Earth interacts with the Sun. This interaction impacts our climate over tens to hundreds of thousands of years, causing regular oscillations known as Milankovitch Cycles.
Let me explain the three different types of Earth-Sun interaction that have an impact on our climate:
Angles of max & min obliquity.
Image credit: NASA
Imagine holding a ball in your hand and putting a sharp stick through the centre and out the other side. Hold the stick and tilt it slightly to one side.
Where the stick enters and exits the ball are the north and south poles, meaning our Earth tilts to one side. However, the angle of this tilt changes over a 41,000 year cycle.
That is obliquity. The Earth’s tilt ranges from 22.1° to 24.5°.
Changes in the Earth’s tilt can alter the amount of ice at the poles.
Imagine the top of your stick is the Arctic and the bottom is the Antarctic. If you increase the tilt, pointing the Arctic towards the sun, this region will get warmer, with less ice. But on the other side of the Earth, the Antarctic will be further from the sun, meaning more ice can form. Therefore, the greater the tilt of the Earth, the greater the temperature difference between the poles.
Different direction of the Earth’s tilt, known as Precession.
Image credit: NASA
Ok… now imagine placing the bottom of your stick on the table. Tilt the stick at an angle, like before, but point the top of the stick in front of you. Now, keeping stick tilted at that angle, and the bottom of the stick on the table, move the top of the stick round in a circle, changing the direction of the tilt, a bit like a spinning top.
This is precession. It is the change in direction of the tilt and it takes the Earth 26,000 years for this tilt to rotate a full circle.
As the direction of the Earth’s tilt moves through its cycle, the timing of our seasons change.
Today, in the northern hemisphere, our summer happens around June/July because that is when we are tilted towards the sun. However, if the direction of the tilt was shifted 180°, we would be furthest from the sun in June/July, and this would become our winter. Thus, the seasons completely flip as the Earth completes one full cycle of tilt.
Now imagine a large circle in the middle of the room. This is the Sun. We all know the Earth moves around the sun, completing one orbit in 365 days (one year). However, did you know that the Earth’s path around the sun is not really circular; it is elliptical (oval)?
Eccentricity maximum and minimum: Low eccentricity with a near circular orbit of the sun (left) and high eccentricity where the orbit is more elliptical (right).
Image credit: NASA
Even more interestingly, the shape of this oval changes in a 100,000 year cycle, sometimes being nearly circular and at other times, extremely elliptical. This means the Earth is further from the Sun at some points of the year.
The eccentricity of Earth’s orbit affects how extreme our seasons are.
When the orbit is most elliptical or stretched, the Earth will be further from the Sun at the extremities of the orbit. Therefore, the difference between the seasons is much greater when the orbit is more elliptical, making the winters colder and the summers warmer.
These three cycles (obliquity, precession and eccentricity) are all occurring at the same time, and interacting with each other to alter the Earth’s climate over long time-scales.
So anyone who has ever told you that climate change is “natural”, and that the Earth has been “constantly moving in and out of glacial and interglacial cycles”, are correct.
However, that is not what we are witnessing today. Natural climate change is not the issue that scientists are urging us to act upon.
They are talking about man-made climate change.
You have just seen the huge timescales of natural climate change for yourself – 26,000 years, 41,000 years, 100,000 years. Compare these numbers to today and the difference is stark – man-made climate change has severely altered the Earth’s climate in just 150 years.
Recent global shifts have made it increasingly important to eliminate lies and empower yourself with the truth, particularly in the field of climate science. It is absolutely critical that people understand the difference between natural and man-made climate change, because this protects us from accepting the endless assurances that this global crisis should be ignored because it is “natural”.
This is not natural – this is man-made, manufactured, anthropogenic.
But just as man is causing it, man can stop also stop it.
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