I wonder what caused a shift in ‘radiative forcing’ 9,000 years ago? Good thing that it happened though, or we would likely not have the civilization we have today.
Sudden shift in ‘forcing’ led to demise of Laurentide ice sheet
CORVALLIS, Ore. — A new study has found that the massive Laurentide ice sheet that covered Canada during the last ice age initially began shrinking through calving of icebergs, and then abruptly shifted into a new regime where melting on the continent took precedence, ultimately leading to the sheet’s demise.
Researchers say a shift in ‘radiative forcing’ began prior to 9,000 years ago and kicked the deglaciation into overdrive. The results are important, scientists say, because they may provide a clue to how ice sheets on Greenland and Antarctica may respond to a warming climate.
Results of the study, which was funded by the National Science Foundation with support from the National Aeronautics and Space Administration (NASA), are being published this week in Nature Geoscience.
David Ullman, a postdoctoral researcher at Oregon State University and lead author on the study, said there are two mechanisms through which ice sheets diminish — dynamically, from the jettisoning of icebergs at the fringes, or by a negative ‘surface mass balance,’ which compares the amount of snow accumulation relative to melting. When more snow accumulates than melts, the surface mass balance is positive.
When melting outpaces snow accumulation, as happened after the last glacial maximum, the surface mass balance is negative.
‘What we found was that during most of the deglaciation, the surface mass balance of the Laurentide Ice Sheet was generally positive,’ Ullman said. ‘We know that the ice sheet was disappearing, so the cause must have been dynamic. But there was a shift before 9,000 years ago and the deck became stacked, as sunlight levels were high because of the Earth’s orbit and CO2 increased.
‘There was a switch to a new state, and the ice sheet began to melt away,’ he added. ‘Coincidentally, when melting took off, the ice sheet began pulling back from the coast and the calving of icebergs diminished. The ice sheet got hammered by surface melt, and that’s what drove final deglaciation.’
Ullman said the level of CO2 that helped trigger the melting of the Laurentide ice sheet was near the top of pre-industrial measurements — though much less than it is today. The solar intensity then was higher than today, he added.
‘What is most interesting is that there are big shifts in the surface mass balance that occur from only very small changes in radiative forcing,’ said Ullman, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. ‘It shows just how sensitive the system is to forcing, when it might be solar radiation or greenhouse gases.’
Scientists have examined ice cores dating back some 800,000 years and have documented numerous times when increases in summer insolation took place, but not all of them resulted in deglaciation to present-day ice volumes. The reason, they say, is that there likely is a climatic threshold at which severe surface melting is triggered.
‘It just might be that the ice sheet needed an added kick from something like elevated CO2 levels to get things going,’ Ullman said.
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If the levels of CO2 were not as high as todays levels, why is the ice not melting rapidly, if what they claim is true?
The paper must be bunkum. Both sea level rise and a number of coastal sediment proxies show that the Laurentide melting was underway ~19000 years ago, and was essentially gone by 9000 ya, despite the Younger Drayas event, which cause (lake Aggasiz breaching the ice dams of the St. laurence) shows the disappearance was from melting and a sharply negative mass balance.
It is as if the author is unaware of Greenland ice, coastal sediment core, moraine dating (like in Wisconsin), and all the other hard physical evidence concerning the event. If his point was some inferred CO2 tipping point, then it is a massive fail.
Either the paper is trash or it is sadly misrepresented in the press release.
‘What we found was that during most of the deglaciation, the surface mass balance of the Laurentide Ice Sheet was generally positive,’ Ullman said.
Oh, sure, they must of found it stuck to the underside of someone’s desk at Oregon State. Maybe they used a model, aka guess work. All the rest of the press release is a fairy castle built on this make-believe premise.
Scientists have examined ice cores dating back some 800,000 years and have documented numerous times when increases in summer insolation took place, but not all of them resulted in deglaciation to present-day ice volumes.
I didn’t know anyone had cored the Laurentide ice sheet and left the results lying around for Oregon State to find.
What’s the proxy for summer insolation?
No mention of a proxy in the paper. They use ‘simulations’ plus celestial mechanics (Laskar et al 2004) for summer insolation.
Love this:
“But there was a shift before 9,000 years ago and the deck became stacked, as sunlight levels were high because of the Earth’s orbit and CO2 increased”
This was my fault. I had just bought a second SUV back in 7000BC.
Thre’s good news here,
“Ullman said the level of CO2 that helped trigger the melting of the Laurentide ice sheet was near the top of pre-industrial measurements — though much less than it is today. The solar intensity then was higher than today, he added.”
Solar intensity is down, so CO2 increase is keeping us from slipping into the next ice age 🙂
About 10,000 years ago, all three Milankovitch cycles were working in harmony to melt the Laurentide ice sheet as well as the Eurasian icesheet. It was all about the Sun, fellas, and CO2 had virtually nothing to do with it; and btw, the beginning of this melting started about 20,000 years with a few setbacks along the way.
Funny, glacial calving used to be a sign that a glacier was stable or growing, but now, through the magic that is “climate science” presto chango – it means just the opposite.
Calving only happens when glaciers end in water. Quite how the Laurentide ice sheet ‘calved’ when most of its edge was on land is beyond me. Precious little calving going on here:
http://www.panoramio.com/photo_explorer#view=photo&position=0&with_photo_id=61852823&order=date_desc&user=4755731
The biggest factor in glaciation is precipitation. Radiation isn’t terribly relevant.
No clue.
The latest fad is the “attribution study” where an expert pronounces that something was caused by CAGW. Today’s California Water News carries an article about an attribution study linking extreme weather with CAGW:
http://www.usatoday.com/story/weather/2015/06/22/extreme-weather-climate-change-global-warming/29124803/
Extreme weather events linked to climate change, study says
Excerpts:
“We have a new normal,” said lead author Kevin Trenberth, a scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., and two fellow scientists. “The environment in which all weather events occur is not what is used to be: all storms, without exception, are different.”
[…]
One expert, Martin Hoerling of the National Oceanic and Atmospheric Administration, who was not involved in the study, criticized that there’s no new research in Trenberth’s study, and that it’s basically an op-ed piece. “The issue of how climate change affects weather is much more complicated,” than expressed in the piece, Hoerling said.
“It is important to emphasize that extreme events are not borne of high vapor vapor and warm oceans alone,” Hoerling said.
[…]
Another expert, meteorologist Michael Mann of Penn State University, also not involved in the study, calls it “a useful contribution to the ongoing discourse on climate change and extreme weather.”
How can climate change affect weather? Climate is average weather over a fixed period. For the climate to change, the weather has to change first. Climate change is the result of a change in the weather.
These people are caught up in their failure to understand their own jargon.
Anthony – your advertisers are getting out of control. They interrupt reading your stuff , both visually, orally, and by shifting your text in the middle of reading it. Takes away from concentration what you have posted, even interferes with writing this reply.
I don’t have any of those issues on my computer.
Me either. Perhaps he has some adware surreptitiously installed.
No issues here either.
Me either, but I do have that happening just in the past few days over at Climate Depot.
It’s the CO2 wot dun it.
The ad has a pause button, click and it stops until page is refreshed.
Use firefox and install add-on “AllBlock”. From the description: “This simple addon lets you instantly remove any content from any webpage. Just (Ctrl+Shift+Click) on any item on a webpage to instantly remove it.”
buddy you have malware of some type.
” ‘It just might be that the ice sheet needed an added kick from something like elevated CO2 levels to get things going,’ Ullman said. ”
So just a little kick from that magic molecule CO2 ended the Wisconsin Glacial Episode. What do they suppose caused the beginning and end of the Nabraskan, Kansan, and Illinoian glacial periods?
https://stevengoddard.wordpress.com/2015/06/22/obama-continues-his-siege-against-reality/#comments
The Northwest passage will be blocked, not due to ice, but due to lowering sea levels as the ice sheets build. Even in this ice thickness picture you can see the ice sheets starting to build as the ice retreats from the Northern Russia region. Warm water from the Atlantic is moving in from the passage between Greenland and Europe. The Atlantic is cooling while the Arctic is warming. It couldn’t be more obvious that this is the end of the Holocene. This is all laid out by Ewing and Donn (1956 Science). The US and Russian military know it. Russia will have the arctic region, and Alaska, which is one of the few places to survive the change from interglacial to glacial. People really need to be talking about this, especially here.
For the record, I’m one of you, a skeptic, a realist. This is natural variation, Milankovitch Cycles..
It’s not supposed to happen till 2100, according to Ole Humlum’s Fourier analysis of GISPII, but go figure..
?w=614
http://www.glerl.noaa.gov/pr/pr_images/glacier.jpg
Nice graphic. I don’t believe I’d realized (or, I’d forgotten) that there was still so much of the ice sheet left only 7,000 years ago. An additional pane, or two, illustrating the full extent of the ice sheet – what, some 29,000 yrs ago, or so, would have been a nice addition to the graphic. Thanks
There’s a major lake (Lake Agassiz) missing northwest of Superior in that graphic and 7 KYA Lake Agassiz was continuous with Lake Ojibwe to the east and which drained into the St. Lawrence river east of Lake Ontario. There was no ice in the area indicated 7,000 KYA. You can only wonder where they get this kind of information(?).
The image is from the great lakes NOAA site. I don’t think any of the other lakes qualify. The ice sheet is what created the Great lakes.
http://www.glerl.noaa.gov/
I have no doubt CO2 was elevated back then. Greening and “insecting” was likely quite rapid as ice sheets everywhere retreated, resulting in ever increasing CO2. Additionally, something else was outgassing and that would be the oceans. When warm waters rise to the surface and sit there, they not only pump heat into the atmosphere, they pump CO2 into the atmosphere.
If this were my investigation, I would be looking for clues about the Arctic Oscillation, why it was stuck for such a long time in one phase, and why it rather rapidly switched to another regime. When it is negative Arctic blasts inundate Canadian territory, freezing its tootsies off. It seems reasonable that ice ages in the NH are characterized by the AO being stuck in negative (along with orbital forcing and other factors). But what goes one way on Earth tends to swing back eventually but not smoothly, and not in equal measures. A positive AO would bring melting temperatures to this very same region and would start in the western part of the Laurentide Ice Sheet which is EXACTLY what has been found. It seems to me that the only thing having enough energy to build and sustain, and then to destroy such large environments is an oceanic-atmospheric teleconnection regime that creates global changes and that are unique to each area of the globe (IE some areas are much colder while other areas are much warmer at the same time when these global regimes are in charge). I think CO2 just rides the tail of these regime shifts.
http://serc.carleton.edu/vignettes/collection/58451.html
http://www.climate.gov/news-features/event-tracker/how-polar-vortex-related-arctic-oscillation
P.G., I agree. And the largest shift in insolation occurs between northern hemisphere (NH) and SH, where one cools as the other warms. The oceans become major conveyors of such heat changes around the globe.
donb @ur momisugly 11:15 am
?w=720&h=636
I would like to understand the bi-polar earth affect. Right now we have the Arctic “heating” and the Antarctic “cooling”. Does this happen on Mars also? Elsewhere? Mars is bi-polar but annually. I can understand how the earth would be bi-polar based on changes in orbit and when perihelion occurs. But no one seems to talk about that. Yet, it shows up on so many graphics of the earth’s temperature.
Maybe someone can point me to some reading.
Thanks.
Per Willis:
I would look at the AO and AAO indices for further elucidation. That said, there are lots of differences between the poles thus they may react differently to oceanic and/or atmospheric oscillations and regime shifts.
“‘What we found was that during most of the deglaciation, the surface mass balance of the Laurentide Ice Sheet was generally positive,”
How do they know that I wonder? It requires knowing the thickness of the icecap, cloudiness, the local lapse rate and the amount of precipitation. There are no reliable proxies for any of these, so it is “models all the way down” as usual.
By 9,000 years ago the Laurentide Ice was already mostly melted. It had been melting for about 10,000 years. The Eurasian icecap was already all gone. I hope that was allowed a negative mass balance a bit earlier by the models, since it didn’t have any ocean to calve into the last couple of milleniums.
How do you know it’s not just an under-specified model…….with funding.
Atmospheric CO2 follows biology.
Biological activity increases follow warming.
Late glacial melting ENDED 9000 years ago. Melting began 19 to 20 thousand years ago.
https://en.wikipedia.org/wiki/Late_Glacial_Maximum
There is something seriously wrong about what this press release is saying about the paper.
Solar TOA insolation in the Northern Hemisphere reached a maximum about 9400 years ago and has been slowly decreasing. But the total decrease (~40 watt/m^2 at 65N) probably was too slow to trigger this early melting.
The mass sheet mass balance is maintained by precipitation rate, which depends on open oceans and ocean currents in the North Atlantic and Arctic. Such currents change. If this precipitation (snow) abruptly decreased, then warm temperatures of NH solar insolation maximum could produce rapid melting. NH cloud albedo may also have been involved.
Melting from small changes in CO2 seems unlikely.
The run up to the peak of solar TOA isolation happened well before 9400 years ago. Roughly 13,000 years ago, perihelion occurred in the beginning of June. It took thousands of years for it to pass the solstice and trail off into latter July.
Orbital eccentricity peaked about 15,000 years ago; orbital obliquity peaked about 12,000 years ago; but climatic precession peaked later. The NH is still in insolation decline from that peak. The month of the peak cannot be determined because of slight changes in orbits of the planets.
“The NH is still in insolation decline from that peak”
..
Not true.
Perihelion is currently in the first week of January.
The last time perihelion was on the December solstice was in 1246 AD. It is advancing toward the March Equinox at the rate of about one day every 58 years. So the NH is not declining, it is on the rise.
donb: “Orbital eccentricity peaked about 15,000 years ago”
eccentricity has a periodicity of 100,000 years and we are near the minimum of eccentricity now. So there is no way eccentricity “peaked” 15,000 years ago unless you mean the minimum is the peak.
NH insolation at 65N depends not only on axial precession (cycle time just under 26,000 years), but also on the tilt of Earth’s axis, which varies over 21.5-24.5 degrees. These BOTH contribute to insolation, and not just where the axis is pointing. Earth’s tilt reached a maximum 9500 years ago.
donb: ” orbital obliquity peaked about 12,000 years ago”
Obiquity changes 1 degree about every 6833 years. We are currently at 23.5 degrees and declining so that would put the peak of obliquity (24.5 degrees) only 6833 years ago. 12,000 obliquity was closer to what it is today but increasing.
To Tom. I mean a peak in insolation produced by eccentricity interacting with other orbital parameters. You are correct that eccentricity is a 100,000 yr plus cycle. However, in considering NH insolation, it is the interaction of ALL parameters that produce the result.
Because Earth is near the minimum in eccentricity, its effect on precession etc., over the next few 10s of thousands of years will be to dampen swings in insolation. Thus, Earth is unlikely to experience a major glaciation anytime soon.
Of course, insolation is only part of the reason Earth has glaciations.
Tom. I think we are comparing apples and oranges. You and Joel are discussing orbital changes individually. When I refer to a maximum or minimum, I mean the effect on solar insolation at 65N. This depends on interactions of all parameters and will not be in phase with any one.
National Science Foundation (actually,National Fr**dulent Science Foundation)with support from the National Aeronautics and Space Administration (NASA) (actually, Never A Straight Answer) sarc/
Science for Sale. Sad.
‘It shows just how sensitive the system is to forcing, when it might be solar radiation or greenhouse gases.’
It shows nothing of the sort. Glaciation and deglaciation are driven by summer solar isolation at high northern latitudes, which in turn drives the rate of change of ice volume, not ice volume itself. These phenomena are not amenable to treatment as a matter of climate sensitivity as in greenhouse gases. The statement is specious. See for example Fig 2 in
http://earthweb.ess.washington.edu/roe/Publications/MilanDefense_GRL.pdf
Look fellows and fellins since we have this no increase in surface temperature but an increase of CO2. Where is all that famous back radiation going? Or not going?
By the way this paper is garbage.
Just shows you get the report you paid for
Notice how strong the Sun is today on June 23, 2015 at the margins of where those glaciers were 14,000 years ago.
The Sun was almost exactly just as strong at the summer solstice 14,000 years ago.
The glaciers were melting furiously at this time of year and all the rivers were flowing south at tremendous rates and new lakes were appearing out of nowhere. The Mammoths had to be very careful or they would drown. The humans who moved in 500 years later, also had to know what they were doing or their camps would be in the middle of a new river or lake.
Why did the glaciers melt back 14,000 years ago. Go stand in the Sun right now and it will be very clear.
Well Bill, I’m sure that the summer solstice occurred, but since the equinoxes precess, can you tell us all when was perihelion in relation to the solstice?
“The Sun was almost exactly just as strong at the summer solstice 14,000 years ago. ”
If you are addressing insolation remember that because the periodicity of Precession is 23,000 years, summer solstice in the northern hemisphere was closer to perihelion 14,000 years ago rather than closer to aphelion as it is today.
There is a large submerged city off the west coast of India that was larger than any city built for another 5000 years. Maybe if the ice sheet hadn’t melted we may be much more advanced!