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MilankovitchCycles

An Astronomical Perspective on Climate Change

Article Updated: 24 Dec , 2015

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Ice cores and deep sea bed cores provide the best available record of changes in global temperature and CO2 content of the atmosphere going back 800,000 years. The data shows a clear periodicity in global temperatures which is thought to be linked to the Milankovitch cycle.

Back in 1920, Milutin Milankovitch, a Serbian mathematician, proposed that fine changes in Earth’s orbit around the Sun could explain an approximately 100,000 year cycle in glaciation seen from geological evidence. The tilt of the Earth’s axis swings slightly over a 41,000 year cycle – the eccentricity of Earth’s orbit moves from almost circular to more elliptical and back again over a 413,000 year cycle – and overlaying that you have not only the precession of the equinoxes, which is an inherent wobble in the Earth’s axial spin over a 26,000 year cycle, but also a precession of the whole of Earth’s orbit over a 23,000 year cycle.

Ice core data does show a rough concordance between glaciation and the synchronicity of these orbital cycles. Even though there’s no significant change in the mean amount of solar radiation reaching the Earth over the period of its annual orbit – the orbital changes can lead to increased polar shadowing and cooling.

Once ice does start advancing from the poles, a positive feedback loop can develop – since more ice increases the albedo of Earth’s surface and reflects more of the Sun’s heat back into space, thus reducing mean global temperatures.

ice coreIt’s thought that what limits the ice advancing is increasing CO2 in the atmosphere – which can be measured from trapped bubbles of air in the ice cores. More ice formation leads to less exposed land area for photosynthesis and silicate rock weathering to remove CO2 from the atmosphere. So the more ice that’s formed, the more CO2 accumulates in the atmosphere – which causes mean global temperatures to rise, which limits ongoing ice formation.

Of course the opposite is true in an ice-melting phase. Ice melting also follows a positive feedback loop since less ice means less albedo, meaning less solar radiation is reflected back into space and mean global temperatures rise. But again, CO2 becomes the limiting factor. With more exposed land, more CO2 is drawn from the atmosphere by photosynthesizing forests and rock weathering. A consequent drop in atmospheric CO2 cools the planet and hence limits ongoing ice melting.

But there lies the rub. We are in an ice-melting phase of the Milankovitch cycle now, where the Earth’s orbit is closer to circular and the Earth’s tilt is closer to perpendicular. But CO2 levels aren’t declining – partly because we’ve chopped a lot of trees and forests down, but mostly because of anthropogenic CO2 production. Without the limiting factor of declining CO2 we’ve seen in previous Milankovitch cycles, presumably the ice is just going to keep on melting as the albedo of the Earth surface declines.

Projected changes in coastlines with 170 metre sea level riseSo you might want to rethink that next coastal real estate purchase – or hope for the best from Copenhagen.

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Lawrence B. Crowell
Member
Lawrence B. Crowell
November 30, 2009 1:18 PM

Anthropic induced global warming is not likely to set up a 170 meter sea level rise. In fact from a climate history perspective it is likely to be a transient spike, where the future will see much the same Milankovitch cycling. The problem we are setting up is that ecosystems may for a couple of thousand years face radical climate shifts and collapse. The problem we are setting up is potentially the next great extinction of life. Our induced global warming will doubtless play a role here, as with our other activities that are reducing the biological capacity of the planet.

LC

Olaf
Member
Olaf
November 30, 2009 2:09 PM

What is the explanation that Earths orbit becomes circular and eleptical? The influences of Jupiter and other planets?

BlueAmberol
Member
BlueAmberol
November 30, 2009 2:37 PM

The biological capacity of our planet is being challenged by our overpopulation. No astronomical function has anything to do with that.

Andrew
Member
Andrew
November 30, 2009 3:03 PM

“Anthropic induced global warming is not likely to set up a 170 meter sea level rise.”

True, but why bring this up? The article doesn’t mention sea level changes at all.

Olaf
Member
Olaf
November 30, 2009 3:14 PM

@BlueAmberol
This article talks about astronomical induced climate change like ice ages. This has no relationship with the global warming we experience now because this one is purely human induced.

bosely
Member
bosely
November 30, 2009 3:38 PM

@Andrew

The article doesn’t mention a 170 meter sea level change but the accompanying final graphic does.

Ivan3man_At_Large
Member
Ivan3man_At_Large
November 30, 2009 4:05 PM

170 metre sea level rise?! As Sean Connery would say: “That musht be shome mishtake?”

According to the Wikipedia article on Sea Level:

If small glaciers and polar ice caps on the margins of Greenland and the Antarctic Peninsula melt, the projected rise in sea level will be around 0.5 m. Melting of the Greenland ice sheet would produce 7.2 m of sea-level rise, and melting of the Antarctic ice sheet would produce 61.1 m of sea level rise. The collapse of the grounded interior reservoir of the West Antarctic Ice Sheet would raise sea level by 5-6 m.

So, by those figures, the sea level rise would be ~74 metres.

Lawrence B. Crowell
Member
Lawrence B. Crowell
November 30, 2009 4:14 PM

The highest order perturbation term is on eccentricity and semi-major axis of an orbit. These changes are due to perturbations from other planets, primarily Jupiter.

LC

Marmot
Member
Marmot
November 30, 2009 9:14 PM

The meta-cause of most environmental destruction is over-population. Humans apparently have a very limited ability to extrapolate from the specific to the general in this regard since I haven’t heard about ZPG in 25 years! Why is population a sacred cow? Are we as yet so near the monkey that we cannot think beyond the sexy thing?

2ru_press
Member
2ru_press
November 30, 2009 11:53 PM
ONE WORD… CLIMATE GATE.. Take “Climategate” at Penn State. That’s what people are calling the controversy surrounding leaked E-mails among climate change researchers that climate change opponents say expose the researchers’ falsification of data. One Penn State professor is involved in the scandal. The Penn State administration plans to investigate Climategate and determine if it needs to take further action, the Daily Collegian reports. A little more than a week ago, E-mails exchanged among an English university’s climate change researchers were illegally obtained from a server and posted online, the report says. Climate change opponents say the E-mails indicate that climate change researchers—including Penn State Prof. Michael Mann—exaggerated or fabricated global warming data. And, according to the report,… Read more »
2ru_press
Member
2ru_press
November 30, 2009 11:57 PM

Penn State officials, who will not discuss the matter, are investigating the controversy. If anything requires further inspection, the school will handle it, a spokesman tells the Daily Collegian. A panel will read every E-mail leaked and determine if climate change critics have any ground for their accusations, the report says.

“I would be disappointed if the university wasn’t doing all [it] can to get as much information as possible” about the controversy, Mann tells the Daily Collegian.

steinauf
Member
steinauf
December 1, 2009 11:01 AM

Really not trying to be nitpicky; but isn’t it well known that the CO2 chart lags the temperature chart by about 800 years? Doesn’t this turn the causal hypothisis on it’s head? Yes, CO2 and temperature could be interdependent, but can CO2 by the lynchpin when it’s a lagging indicator?

@IVAN3MAN
Your figure on sea level rise requires the application of the principle of superposition, which requires linearity. I’ve seen too many people throughout this debate confuse and ignore basic principles such as this. Models can be linear, but there is no such thing as a linear system in reality; and climate is anything but.

Dark Gnat
Member
Dark Gnat
December 1, 2009 11:39 AM

Looks like the current warming period is right on time.

jackcroww
Member
jackcroww
December 1, 2009 12:04 PM

Congratulations. Your lame and heavy-handed Climate Scientology scare tactics in this article have convinced me to never visit UniverseToday.com again and to unsubscribe from the RSS feed.

Ivan3man_At_Large
Member
Ivan3man_At_Large
December 1, 2009 12:40 PM

@ steinauf,

I never stated that the climate follows linear models, and I realize that, in the real world, it is subject to the chaos theory — the “butterfly effect”. I merely pointed out, above, what would be, in the worst-case scenario, the maximum sea-level rise according to those figures from Wikipedia.

Ivan3man_At_Large
Member
Ivan3man_At_Large
December 1, 2009 1:00 PM

jackcroww:

Congratulations. Your lame and heavy-handed Climate Scientology scare tactics in this article have convinced me to never visit UniverseToday.com again and to unsubscribe from the RSS feed.

I wish “Anaconda” would do likewise!

Lawrence B. Crowell
Member
Lawrence B. Crowell
December 1, 2009 6:05 PM

It is curious that there are two scientific areas which really get people angry: Evolution and climatology. Why? because they upset preconceptions about things held by people with conservative minds.

LC

RUF
Guest
RUF
December 1, 2009 6:09 PM

The cat is finally out of the bag with the revelation of Global Warming Hoaxers fudging data to fit their religious belief in man-made warming. Apparently, there is no warming — man-made or not. Just fraudulent propaganda.

Too bad the news of the hoaxers is not being widely reported. (Guess they’re too afraid that might constitute “peer-review.”)

RUF
Guest
RUF
December 1, 2009 6:13 PM

and earlier post, and Wikipedia says:

“So, by those figures, the sea level rise would be ~74 metres.”

So what — that’s only an inch or two, right?

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