What makes Earth Scientists so sure that the current climate crisis is man-made? HESCOR Ringvorlesung student Bethan Callow explains why scientists have a lot of certainty about our role in current global climate changes!
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What if climate change is not just man-made? What if the current climate change is just one of Earth’s natural climate cycles? These are questions that are often asked by those sceptical of climate change. So what does the science say?
The Earth actually does naturally warm and cool! One way we know this is because of Milankovitch cycles. These were articulated by Milutin Milankovitch, a Serbian scientist [(NASA Science , 2020)], who found a connection between Earth’s position in relation to the sun and the Ice Ages [(Spiegel et al., 2010)]. So, is climate change caused by humans or are we just in a period of natural warming? Or is it something between the two? Let’s get further into it.
Milankovitch cycles have 3 parts: eccentricity, obliquity, and precession.
First of all, eccentricity. Eccentricity is the change in the Earth’s orbit from nearly circular to slightly like an oval – also known as ‘slightly elliptical’ [(NASA Science Editorial Team, 2020)].
Next we have obliquity. Obliquity is a weird word describing the Earth’s tilt on its axis. Even though on a traditional map everything is perfectly straight, the Earth is actually at an angle like you would see on a globe in a classroom. This tilt changes the strength of the seasons[(NASA Science, 2020)].
Finally, precession. Precession is also known as the ‘wobble’ of the Earth. It is more complex than the other two. The axis or orbit ‘wobbles’ slightly away from where it normally is due to gravitational influences from the Moon, Saturn and Jupiter. [(NASA Science, 2020)],
But why do any of these matter? Why does that have an effect on whether the Earth is warming or cooling?
Essentially, eccentricity (or the Earth’s orbit changing) affects how much sunlight reaches the Earth. This sunlight can also be called ‘radiation’ or ‘energy’ [(NASA Science Editorial Team, 2020)].
The other two affect the strength and timing of the seasons. But altogether, all 3 effects change the total radiation reaching the Earth in a given latitude or season. This is a huge factor for the climate on Earth and the reason why ice ages occur.
Because we are approaching the Earth’s most circular orbit, we are currently in an“Interglacial Period” called the Holocene [(Berger and Loutre, 2002)] that started 12,000 years ago. This means warm climates, but we are also in a long-term cooling trend, due to the increasing tilt of Earth’s axis.
Hang on, go back a second. Did I hear the word “cooling”?
Yes you did! We are meant to be in a period of slow cooling if we were purely following the Milankovitch Cycles without any external influences. Crazy right?! And the next “Ice Age” is still tens of thousands of years away (Berger and Loutre, 2002). So this won’t save us from global warming. So how can we use Ice Ages as an excuse for the current climate change we experience? [(NASA Science Editorial Team, 2020)].
Now you can understand where the climate scepticism comes from. But natural changes in the climate take place over a long time – thousands of years, or even longer. Which gives us even more reason to look at human actions to explain the current rapid climate change we experience – it’s not in Earth’s natural cooling and warming cycles.
So now you know about the Milankovitch cycles and why they don’t say climate change is normal, but rather, it’s an anomaly of the Earth. We are out of sync with Earth’s cycles, so now it is time to act!
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