Italian cave makes sense of the change in Earth’s ice age rhythm

About a million years ago, ice ages got much longer—what changed?

Read the whole story

 

[stine]

According to those graphs, we're still on the upward portion of the curve. Is there any clue what makes the curve change direction? Also, where do they predict we are on the curve?

 

[JohnDeL]

According to those graphs, we're still on the upward portion of the curve. Is there any clue what makes the curve change direction? Also, where do they predict we are on the curve?

Your questions are all answered in the article. If you need more, read this.

 

[rabish12]

According to those graphs, we're still on the upward portion of the curve. Is there any clue what makes the curve change direction? Also, where do they predict we are on the curve?

JohnDeL's post covers most of this, but it's also worth pointing out that you're reading the graph backwards. The X axis is age, and the most recent period is on the left (where the normalized forcing is in decline).

 

[Fatesrider]

According to those graphs, we're still on the upward portion of the curve. Is there any clue what makes the curve change direction? Also, where do they predict we are on the curve?

You're looking at the wrong fucking side of the graphs, dude. Those are labeled by age in kiloyears, from now, on the LEFT SIDE to a million years ago on the right side.

It's showing that we're on the down-swing, when our temperature is going UP significantly over the last 150 years (almost all of it in the last 30 years).

The scale is too large to see that effect over that period of time.

The Earth should be heading for a cooler-than-normal swing. It's going the other way.

[Edit: crap.. Ninja'd by seconds.]

 

[Zorro]

All sorts of little details.

Like glaciers pressing down the crust, and water moving around.

Albedo of the earth surface reflecting energy back in too space more or less.

Earth is always doings something different than last year.

 

[danielravennest]

According to those graphs, we're still on the upward portion of the curve. Is there any clue what makes the curve change direction? Also, where do they predict we are on the curve?

The age scale on the graph is in (ka) or "kiloannum", which means thousands of years ago. People who study the past commonly reference the zero point to when they wrote the paper.

So the external forcing today is on the left edge of the graph at the zero point in age, and it is a bit below zero. That's why people say we should have been in a gradual cooling climate if it were not for human-caused changes. The upper curves are the individual forcings (polar precession and polar tilt), and the lower curve is the sum. The dotted vertical line at 12 ka (12,000 years ago) was the previous peak forcing, which matches the end of the last ice age.

 

[spacespektr]

If you’ve ever run short of sleep long enough that you successfully slept through an alarm undisturbed, perhaps you can relate.

Scott? We’re you late filing this article?

 

[Caelicola]

So, the researcher using Italian cave data was named Petra Bajo? Nice.

 

[kurama101]

A viable explanation for the transition from 40ka to 100ka glacial cycles was found about a year ago. As the ice sheets removed the topsoil down to bedrock they slowed down due to the increased friction, and also increased in albedo due to the lack of soil and dust being picked up by the wind and deposited on top of the ice. The slower speed increased the ice sheets resilience to warmer periods, and the increased reflectivity made those warm periods less warm.
This mechanism was successfully put into climate models to accurately predict the last 3Ma of climate.
https://advances.sciencemag.org/content/5/4/eaav7337

 

[carrier1589]

Scott writes: "The general outlines of the ice ages of the last several million years are pretty well understood. The timing of the glacial cycles has been controlled by cycles in Earth’s orbit, with the temperature swings amplified by feedbacks in the Earth system via raised and lowered greenhouse gas concentrations."

While CO2 content in the atmosphere and oceans is important in glaciation, general climate and ocean acidification, changes in ocean currents over geologic time are clearly more significant in initiating or concluding continental glaciation. I believe you may have overlooked the significance of changing ocean currents in this introductory explanation. I humbly offer these three articles as evidence of the significance of changing oceanic currents and the impact on continental glaciation.

http://www.earthtimes.org/climate/clima ... ions/2731/

https://www.nytimes.com/1992/02/04/scie ... -ages.html

https://www.nature.com/scitable/knowled ... -25858002/

 

[brduffy]

"with the age of each datapoint known to within 7,000 years."

"A much-used seafloor core compilation put the length of the ice age in this time period at 92,000 years, but this new record shortens that to about 85,000 years."

That part makes me wonder.

 

[numerobis]

"with the age of each datapoint known to within 7,000 years."

"A much-used seafloor core compilation put the length of the ice age in this time period at 92,000 years, but this new record shortens that to about 85,000 years."

That part makes me wonder.

There’s equal probability of being high or low by 3,500 years.

EDIT: kind of silly that people are downvoting you. I had to check the paper to make sure I was interpreting "within 7,000" correctly, since it could be interpreted either way.

 

[nosmadar2016]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

EDIT for Clarification: I'm not a denier, I just want to fully understand how the data was handled. Which was answered. Thanks for the responses.

 

[07stiltd]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

Presenting the data in terms for the lowest common denominator not only mutes some of the impact of the findings, it's playing to their game. These people have not approached climate research from a reasonable position. Expecting simplified information to change the minds of the ideologically entrenched is a disservice to the research. These folks are locked in and no new data aside from a palm tree sprouting in their yard in MN (which they would contort into a good thing) will change their view. They aren't interested in the science. They're worried about the costs, full stop

 

[numerobis]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

It’s just adding up two theoretical curves and putting it on a graph. The two curves are the same units, so why not add them up?

Deniers don’t care about the methodology, only about the results, so who cares what they’ll say about the methodology. Or really about anything.

 

[ScottJohnson]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

Maybe this analogy helps:

It's a bit like first plotting my paychecks and the bills I pay separately from my wife's paychecks-in/bills-out, and then combining them to show our total paychecks-in/bills-out cycle.

(Oh, I'm supposed to fit the eccentricity cycle into this analogy... Uhh, let's say we also sell some stuff at a craft show every 3 months, but that cash income isn't being reflected in the above calculation for now. And we're trying to figure out... why we seem to buy a bottle of scotch four times a year, on average...)

 

[numerobis]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

Maybe this analogy helps:

It's a bit like first plotting my paychecks and the bills I pay separately from my wife's paychecks-in/bills-out, and then combining them to show our total paychecks-in/bills-out cycle.

(Oh, I'm supposed to fit the eccentricity cycle into this analogy... Uhh, let's say we also sell some stuff at a craft show every 3 months, but that cash income isn't being reflected in the above calculation for now. And we're trying to figure out... why we seem to buy a bottle of scotch four times a year, on average...)

She sells every two and a half weeks and you sell every four weeks. Also there’s a recurring billing error that credits and later debits a bit of money every four months, but not seemingly enough to affect your buying habits.

 

[Johnny Vector]

But rather than look at two overlapping piles of spaghetti, they mixed the effects of tilt and precession into a single curve, laying that up against the full climate record.

Assuming (and please correct me if I'm wrong) that the statement above implies that there was some mingling of data; isn't that what gets all of the deniers screaming "See, it's a HOAX!...the data was cherry picked"?
Can we please get more details about how they were mixed and why it was OK to do so in this instance?


P. S. (When in fact typically it's the deniers doing the fruit harvesting).

Maybe this analogy helps:

It's a bit like first plotting my paychecks and the bills I pay separately from my wife's paychecks-in/bills-out, and then combining them to show our total paychecks-in/bills-out cycle.

(Oh, I'm supposed to fit the eccentricity cycle into this analogy... Uhh, let's say we also sell some stuff at a craft show every 3 months, but that cash income isn't being reflected in the above calculation for now. And we're trying to figure out... why we seem to buy a bottle of scotch four times a year, on average...)

She sells every two and a half weeks and you sell every four weeks. Also there’s a recurring billing error that credits and later debits a bit of money every four months, but not seemingly enough to affect your buying habits.

See that's why I only drink Ockham's Single Malt.

 

[SailRick]

A good overview of Milankovitch cycles is here.

Milankovitch Cycles and Their Role in Earth's Climate

https://climate.nasa.gov/news/2948/mila ... s-climate/

---------

As to the frequent claim by deniers that CO2 increases follow warming, rather than cause it, the study by Shakun et. al. found that when the last glacial period ended, over 90% of the warming happened after CO2 increased.
----------------------

"The direct effect of Jupiter and Saturn (Milankovitch cycles) is to cause a 10-ppm change in CO2. The feedbacks in Earth’s climate do the rest to cause the 100-ppm CO2 change.

If planets 100’s of millions of miles away can trigger 120-m tides, is there anything that human civilization is doing today that could trigger feedbacks in our sensitive, unstable environment?

By burning fossil fuels we’ve increased CO2 by 130 ppm in 200 years, 13 times the initial CO2 pulse during an ice-age cycle."

http://www.skepticalscience.com/SkS_Ana ... Earth.html

 

[cellocgw]

How do all these mini-cycles compare with cycles measured over, say, 50-million year spans? I thought that the entire period discussed here has polar ice caps, for example; somewhere back in preJurassic time wasn't the entire planet free of ice for millions of years?

 

[ScottJohnson]

How do all these mini-cycles compare with cycles measured over, say, 50-million year spans? I thought that the entire period discussed here has polar ice caps, for example; somewhere back in preJurassic time wasn't the entire planet free of ice for millions of years?

There aren't really cycles over those time spans. The long-term trends like you're talking about have a lot to do with the random-bumper-car nature of tectonic plates moving around. For example: https://meincmagazine.com/science/2019/03 ... tectonics/
https://meincmagazine.com/science/2016/04 ... e-equator/

 

[Uxorious]

About a million years ago, ice ages got much longer—what changed?

Certainly not global climate change... that would be impossible as there was no human pollution back then.