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Paleoclimate Thread

Past Climate Change Was Caused by the Ocean...

Unread postby TemplarMyst » Mon 27 Oct 2014, 20:26:30

Ran across this this morning, thought it might provoke a few thoughts...

Past Climate Change Was Caused by the Ocean, Not Just the Atmosphere

In their study, the researchers say the major cooling of Earth and continental ice build-up in the Northern Hemisphere 2.7 million years ago coincided with a shift in the circulation of the ocean – which pulls in heat and carbon dioxide in the Atlantic and moves them through the deep ocean from north to south until it’s released in the Pacific.

The ocean conveyor system, Rutgers scientists believe, changed at the same time as a major expansion in the volume of the glaciers in the northern hemisphere as well as a substantial fall in sea levels. It was the Antarctic ice, they argue, that cut off heat exchange at the ocean's surface and forced it into deep water. They believe this caused global climate change at that time, not carbon dioxide in the atmosphere.


Now I'm sure because I tried to limit the length of the title someone will think I'm a denier, which is certainly not the case. I think this article just adds a bit more information to the discussion of a very complex issue.

I haven't had a chance to dig into it in depth yet. Just thought it might be food for thought here.
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby GHung » Mon 27 Oct 2014, 22:31:11

There have been numerous reasons climate change occured on Earth, almost all bad for whatever lifeforms existed at the time. Human-caused/accelerated climate change won't be any different. Playing Russian roulette with our biosphere doesn't seem like a good demonstration of sapience, but what do I know? I'm just a pyro-ape.
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby dissident » Tue 28 Oct 2014, 00:12:01

It's not a case of either/or. The dynamical system is the combined ocean-atmosphere one. The fixation on the atmospheric sub-component is an endless source of confusion. For example the large scale heat energy exchange associated with ENSO is misinterpreted as an example of variability in the sense of thermal energy variability. If you track the total energy of the system this variability disappears and what matters is that the system is accumulating thermal energy thanks to human pumping of greenhouse gases into the atmosphere and increasing the trapping of solar energy.

This press release is written by some journalism major and is full of typical media spin. Phoney controversy and fake opposing viewpoints to sensationalize the story. We entered the current ice age thanks to the long term decline in atmospheric CO2 over the last tens of millions of years (CO2 fell low enough about 35 million years ago for Antarctica to ice over) and the closing of the Panama channel about 4 million years ago. There was actually a surge in warming after the closing of the channel but then the cooling reasserted itself. It is not surprising the ocean circulation changed during the early stages of the ice age. An important point is that the ocean circulation has been in the same regime since 2.7 million years ago and the glaciation cycles are due to orbital variations and associated insolation changes. CO2 is an amplifier for this cycle since colder oceans mean more CO2 is dissolved into the them and vice versa. (A common denier talking point "proving" that temperature drives CO2 changes).

There is no doubt the current climate change is greenhouse gas driven. It looks like we will pump enough CO2 and unleash enough cryospheric CH4 to disturb the system for hundreds of thousands of years (see David Archer's papers). So we may see ocean circulation changes on a scale not seen for 2.7 million years. How the ocean circulation will change is not clear. Perhaps the Rutgers researchers are collaborating to do some ocean simulations.
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby drwater » Tue 28 Oct 2014, 14:54:35

Dissident,

Thanks for the details. It appears that the researchers are hypothesizing that the planet flipped to the current cooler state due to deep ocean circulation changes, which were caused by an increase in Antarctic ice. The real issue this raises is whether the current warming could cause the deep ocean circulation to flip back to the warmer state. That would cause serious problems. So far even though Antarctic ice volume is decreasing, the extent of ocean ice is slightly increasing. Let's hope nothing crops up to change the circulation pattern.
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby dissident » Tue 28 Oct 2014, 22:36:47

drwater wrote:Dissident,

Thanks for the details. It appears that the researchers are hypothesizing that the planet flipped to the current cooler state due to deep ocean circulation changes, which were caused by an increase in Antarctic ice. The real issue this raises is whether the current warming could cause the deep ocean circulation to flip back to the warmer state. That would cause serious problems. So far even though Antarctic ice volume is decreasing, the extent of ocean ice is slightly increasing. Let's hope nothing crops up to change the circulation pattern.


An important detail is the time scale. In the next century we are not going to see any major shift of the circulation. It really would take over 1000 years for the oceans to flip into some new circulation state. The abyssal currents are diffuse and extremely slow. All the "action" is near the surface where all the forcing by eddies induced by wind stress and solar heating variations is active. One of the expected results of warming is for global ocean circulation to get shallower and for the efficiency of heat exchange with deeper, colder waters to become lower.

http://www.isciencetimes.com/articles/6 ... rrents.htm
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby Graeme » Wed 29 Oct 2014, 17:54:59

New study shows three abrupt pulse of carbon dioxide during last deglaciation

A new study shows that the rise of atmospheric carbon dioxide that contributed to the end of the last ice age more than 10,000 years ago did not occur gradually, but was characterized by three "pulses" in which C02 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which C02 levels rose about 10-15 parts per million – or about 5 percent per episode – over a period of 1-2 centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes.

The finding is important, however, because it casts new light on the mechanisms that take the Earth in and out of ice age regimes. Results of the study, which was funded by the National Science Foundation, appear this week in the journal Nature.


The researchers say that the increase in atmospheric CO2 from the peak of the last ice age to complete deglaciation was about 80 parts per million, taking place over 10,000 years. Thus, the finding that 30-45 ppm of the increase happened in just a few centuries was significant.

The overall rise of atmospheric carbon dioxide during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. However, the researchers say that no obvious ocean mechanism is known that would trigger rises of 10-15 ppm over a time span as short as one to two centuries.

"The oceans are simply not thought to respond that fast," Brook said. "Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don't yet know about."
One reason the researchers are reluctant to pin the end of the last ice age solely on CO2 increases is that other processes were taking place, according to Marcott, who recently joined the faculty of the University of Wisconsin-Madison.

"At the same time CO2 was increasing, the rate of methane in the atmosphere was also increasing at the same or a slightly higher rate," Marcott said. "We also know that during at least two of these pulses, the Atlantic Meridional Overturning Circulation changed as well. Changes in the ocean circulation would have affected CO2 – and indirectly methane, by impacting global rainfall patterns."


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Re: Past Climate Change Was Caused by the Ocean...

Unread postby TemplarMyst » Wed 29 Oct 2014, 22:14:36

I didn't get a chance to fill out some thoughts I had when I made the original post. I had intended to tie this research to Recent Global-Warming Hiatus Tied To Equatorial Pacific Surface Cooling. Now sure, it's not exactly the same thing, but the Rutgers research brought to mind the basic idea of the role the oceans play in the climate in general, as well as some of the areas where there are gaps in the understanding of such a complex system.

And, to further continue on a mildly wandering path, covered in other recent posts on the Environment forum, I thought the potential surface cooling to be a nice addition to the discussion over the role of aerosols in the surface temperature "hiatus", as well as the general idea the heat has gone into the oceans and whether or not the deep oceans are actually heating as much as assumed.

In other words, just some more research on it all. And if I didn't make it abundantly clear in my first post, I think the current climate change is being caused by us, and things are looking pretty nasty now and going to get nastier as we go.
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Re: Past Climate Change Was Caused by the Ocean...

Unread postby dissident » Wed 29 Oct 2014, 23:09:45

Yes, indeed the so-called hiatus is a decade and longer time scale variation in the temperature trend that must be linked to the oceans. The atmosphere cannot retain dynamical memory for decades. There can be long term changes due to alterations in the chemical and hence radiative composition, but the life span of storm systems and baroclinic eddies (low pressure systems) is just too short.

Also, the "hiatus" is not there if a proper running mean is done on the temperature trend data. There was a surge of warming from around 1995 to 2005 but now we are back to the trend line from 1980 to 1995. Maybe there will be an actual negative trend or prolonged zero trend in the coming decades. But that will be linked to some large-scale heat sequestration in the oceans since the radiative properties of the atmosphere are not going to revert to 1960s levels in the coming century and longer.

We are still in a state where the ocean circulation connects the surface waters to the deep waters quite extensively. The flip into the shallow surface circulation mode is not going to happen in the next several centuries due to the very long dynamical adjustment of the oceans.
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Paleoclimate Thread

Unread postby Keith_McClary » Tue 30 Jun 2015, 15:02:16

June 30, 2015
Study shows Lake Mega-Chad dried up far more quickly than thought
For many years, Earth scientists have theorized that the remains of Lake Mega-Chad (a huge lake that once existed where Lake Chad now sits in central Africa—on the borders of Nigeria, Chad, Cameroon and Niger) provide the fertilizer for the Amazonian rainforest, thousands of miles away in South America—without a constant infusion of nutrients the lush vegetation would disappear because nutrients are washed away by the constant rainfall. This new study of Lake Mega-Chad now casts some doubt on that theory.
By studying the geography of Lake Chad and the area around it using satellite imagery to make out ancient shorelines, an area that was once covered by water (the Bodélé basin) the researchers found that the region underwent a drying spell some 5,000 years ago, that has lasted to this day. Prior to that, the area had been humid, with a lot of rain, which fed Lake Mega-Chad, the largest lake in the world at that time. But then, something happened and the rains began to slow, which caused the lake to shrink rapidly, just a thousand years ago, much more recently than has been thought. When the lake shrank, it left behind thousands of years of silt deposits (which dried up and formed sand dunes) which has been carried by the wind, perhaps all the way to South America—but only for the last thousand years—which begs the question, where was the Amazon basin getting its fertilizer before that time?

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(Image link)
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Today all that remains of this enormous lake is Lake Chad. Soon even this whisper of a grander past will vanish – Lake Chad has shrunk by 95% in just the last 50 years. This is highly unfortunate as 30 million people rely on its water for drinking and irrigation.
https://toknowistochange.wordpress.com/tag/lake-chad/
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Re: Paleoclimate Thread

Unread postby dohboi » Tue 30 Jun 2015, 15:12:33

Cool idea for a thread!

Isn't that top map a bit off, since 5000 years ago, not only was there a huge lake in what's now the southern Sahara and Sahel, but the Sahara wasn't quite the desert it is now then. Or am I remembering this wrong?
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Re: Paleoclimate Thread

Unread postby Keith_McClary » Tue 30 Jun 2015, 15:39:13

dohboi wrote:Cool idea for a thread!

Isn't that top map a bit off, since 5000 years ago, not only was there a huge lake in what's now the southern Sahara and Sahel, but the Sahara wasn't quite the desert it is now then. Or am I remembering this wrong?
I think it's the lakes superimposed on a current map. (It also shows the countries. :lol: ).
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Re: Paleoclimate Thread

Unread postby dohboi » Tue 30 Jun 2015, 16:15:46

D'oh!

Yeah, I missed that. I guess that's useful for people familiar with modern geography of the place to figure out exactly where these lakes were. It is quite a stunning map, in any case.
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Re: Paleoclimate Thread

Unread postby Peak_Yeast » Tue 30 Jun 2015, 19:06:37

Thanks for posting this. I love these types of information about our "recent" climates.
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Re: Paleoclimate Thread

Unread postby Apneaman » Wed 01 Jul 2015, 05:30:55

Paleoclimate: Climate Change Through Time

http://serc.carleton.edu/NAGTWorkshops/ ... imate.html
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Re: Paleoclimate Thread

Unread postby Apneaman » Wed 01 Jul 2015, 05:33:32

Peter Ward , Professor, Sprigg Institute of Geobiology, The University of Adelaide


Everything you need to know about Mass Extinction, Sea Level Rise and Amplification


https://www.youtube.com/watch?v=r4jKo2-dS4M
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Re: Paleoclimate Thread

Unread postby Apneaman » Wed 01 Jul 2015, 05:44:40

Tipping Points & Extinction Events - Dr. Peter Ward - 8 min


https://www.youtube.com/watch?v=i_cH_ALE-Fk
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Re: Paleoclimate Thread

Unread postby Apneaman » Wed 01 Jul 2015, 05:46:03

Big Think Interview With Peter Ward


https://www.youtube.com/watch?v=OPRUggIb-NI
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Re: Paleoclimate Thread

Unread postby Apneaman » Wed 01 Jul 2015, 05:52:49

Volcanoes, Not Meteorite, Killed Dinosaurs, Scientist Argues

http://www.livescience.com/25324-volcan ... saurs.html
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Re: Paleoclimate Thread

Unread postby Keith_McClary » Wed 01 Jul 2015, 13:21:25

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Re: Paleoclimate Thread

Unread postby dissident » Wed 01 Jul 2015, 17:14:12

Apneaman wrote:Volcanoes, Not Meteorite, Killed Dinosaurs, Scientist Argues

http://www.livescience.com/25324-volcan ... saurs.html


It's ridiculous how this is treated as an either/or situation. Tens of thousands of years of volcanic activity that we do not see today cannot be fobbed off as secondary in terms of CO2 and SO2 compared to a meteorite impact. The meteorite would have loaded the atmosphere with lithogenic aerosols and CO2 released from both land fires and melting of crustal rock. Most of the aerosol would have sedimented and been washed out by convective scavenging within two years. The CO2 release would be much smaller compared to the Deccan traps considering how much rock was melted and how it was melted (from above, which is not the same as volcanic CO2 release).

If you go to the Gubbio, Italy, location of the original discovery of the iridium layer back in the 1970s you will see thick layers of pink limestone with which it is associated. The pink limestone indicates anoxic ocean conditions during its formation and from the thickness of these layers (a good 30 cm thick) you can tell that this was not some 2-year blip but lasted tens of thousands of years. The team behind this paper has done a great job clarifying the timelines of the Deccan traps and the meteor impact. It is clear that the Deccan traps formation started before the impact and that they account for most the impact on the climate. The meteor theory has lots of popular appeal. But science is not a popularity contest.
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