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.
###
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
What is this BS ‘radiative forcing’ ? It has no place in physics,but then the author is a qualified environmental “scientist”.
Folks, this is a news report written by a journalist who quite likely could not identify Antarctica on a map where it wasn’t at the bottom and colored white. I assume that the study authors had some data of some sort to base their conclusions on. Unfortuately the nature of the evidence has been entirely lost in this writeup. Until someone finds either the paper itself or an intelligent summary of its content, discussion this looks to me to be a complete waste of time.
David J Ullman (Oregon State University, Corvallis) on …
hope this works, you can get to some of his Papers from here.
michael
http://www.researchgate.net/profile/David_Ullman
try try again
Thanks Mike!
It would appear that the ‘forcings’ are based on GISS Model E.
The paper is a masterpiece of speculation.
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.
Ummm…. question. WHY didn’t Greenland respond? Same sunlight, same forcings, same CO2. A giant counterexample right in their own claims.
Greenland, like Antarctica, is surrounded by water. That may be the key factor in the ice sheet there not melting.
How do the glaciers know they are surrounded by water? The factors cited were solar, forcings and CO2.
“What we found was that during most of the deglaciation, the surface mass balance of the Laurentide Ice Sheet was generally positive”
There was no link to the actual research so I still haven’t read what the evidence for this is. It doesn’t seem likely though. There were areas south of these ice sheets that were a lot wetter eg. SW USA, North Africa, middle east. The wind patterns meant that the ice sheets were in a sort of rain shadow. Siberia now gets about the same average precipitation as semi-arid regions and the Antarctic.
Also, dynamic suggests that the terminus of glaciers were melting quicker but much of the drainage of the ice sheet in the south was down the Mississippi as a river not glaciers ending in a bay. Surely then, there is some evidence that the ice sheet in the NE US didn’t start to recede until late? All the evidence points to the ice sheet receding from the south to the north with proglacial lakes forming and bursting their dams.
I would go with greater rainfall. It takes a lot of energy to melt ice and if the precipitation is rain not snow, then the pools of water on the ice absorb more radiation rather than reflect it. A lot of summer rain when shallow pools of water are more likely to dry out than freeze over seems like a better reason than the ice flowing to the sea quicker.
Robert B, I believe you hit the nail on its head. Early March cold rain will melt snow pack. Watch out for flooding if the ground is still frozen,
Today we can sunbathe where there used to be a mile of ice. Almost nobody is sunbathing in Greenland at any time of the year. The conditions aren’t nearly the same.
Nuuk in Greenland is currently enjoying some fine settled weather! Not very warm but the sun is out!
http://www.weather-forecast.com/locations/Godthaab/forecasts/latest
http://arcticomm.gl/webcam/arcticomm_webcam.jpg
Yes. Glaciers must have precipitation, and both are surrounded by water, whose evaporation is carried above them by prevailing wind. In contrast, Alaska is located far from prevailing winds carrying moisture from the north Atlantic. And when the Arctic ocean was frozen in the last glaciation, much of Alaska remained unglaciated, in sharp contrast to Canada.
Yes, ,something happened way back then. but something is always happening.
Wouldn’t it be nice if the PR people who write these releases recognised that all journal articles are contributions not decisive works that end discussion. It cannot be said that the authors ‘found’ what they propose. Rather, they ‘suggest’ that this is what happened.
Yes, I know it’s a small point…
It is a fact that there is cyclic climate change in the paleo record with a periodicity of 1500 years plus or minus 500 years. In the last 15 years climatologists have confirmed that cyclic changes are global. The cyclic changes occur during the interglacial period and during the glacial period. One of the surprises in the climate record (Discovered in 1993 by analysis of the Greenland Ice Sheet Project 2 ice core, paleo climatologists did not trust project 1’s ice core analysis and hence drilled another core at an ideal location, 30 miles from project 1’s location, to confirm project 1’s analysis) is the discovery of very large abrupt climate change events.
The abrupt climate change events are capable of and do end and start the interglacial periods (Interglacial periods start and end abruptly not gradually). There are dozens of different observational and analysis results that support the assertion that the cyclic abrupt climate change is caused by cyclic changes to the solar cycle which in turn is caused by/trigger by the motion of the sun by the large planets which explains what regulates the period of the cycle.
http://www.agu.org/pubs/crossref/2003/2003GL017115.shtml
The cyclic change to the sun when it occurs, causes a small, medium, or very large change to the earth’s climate. The observational fact all of the climate changes – small, medium, and super large – occur along the same series in time (imagine a sequence in time where the size of the next in the sequences varies in dependence on what happens to the sun) for the next 1500 year plus or minus 500 year climate change and the fact that there are small, medium, and immense cosmogenic isotope changes that correlate with the cooling and warming events are a couple of the observations that supports the assertion that the sun is causing the cyclic climate changes.
Early indication of the start of cooling will be expansion of deep blue in this diagram. It will be interesting to see how the cult of CAGW initially tries to spin away abrupt cooling.
http://www.ospo.noaa.gov/data/sst/anomaly/2015/anomnight.6.22.2015.gif
The strongest cyclic climate changes are called Heinrich events which is a idiotic naming conversion. A cyclic physical event should not be named after the person who discovered the event. Use a naming convention that provides information concerning the cause of the event. Heinrich events initiate and terminate interglacial periods.
The small and medium cyclic climate changes are called Dansgaard-Oeschger events. Again an idiotic naming convention. (Wally Broeker started the idiotic naming convention and sent the climate community off into left field with suggestion that North Atlantic Drift current could somehow cause a Heinrich event. (It is an order of ten too small.)
If and when the planet starts to unequivocally cool, I will present in serial form a Coles note summary of what is happening and its theoretical implications.
Great stuff – – that’s exactly what my gut came to realize simply through studying the history a bit. Do you have a link to the actual study – would appreciate.
Ah, speculation. I’m surprised more climate scientists don’t play roulette
“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.”
Whaaaat?? Only at Oregon State would MORE accumulation result in LESS mass. Perhaps that only happens during deglaciation?? Wow – I am glad I graduated from the UofW! Perhaps the Physics department at OSU needs to be notified that the Climatology dept has discovered a new law of physics – one where adding more mass results in less total!
I assume only that the quote was correct.
And this is PhD work??
‘It just might be that the ice sheet needed an added kick from
something like elevated CO2 levels to get things going,’ Ullman said.
Yes, it just might be, maybe, perhaps, possibly.
[quote] …the massive Laurentide ice sheet that covered Canada during the last ice age initially began shrinking through calving of icebergs, [/quote]
How can a shrinking ice sheet calve icebergs?
The last glaciation greatly lowered sea level and exposed continental shelf (bare land), on which glaciation formed. As ice melted and the sea rose, this ice was broken into the sea.
That process may work for coastal areas, but in places like Pennsylvania, Ohio, Indiana, Illinois, Wisconsin, Iowa, and the Dakotas, for example, it would not.
There is considerable evidence that glaciation in the US melted from south to north over time, and as you infer, this was due to Temperature and increasing solar insolation, not the sea.
As it is clear that CO2 always lags temperature changes, it is ingenuous to pretend that it triggered anything back then. As temperatures crashed while atmospheric CO2 was still high, it is clear that CO2 not only cannot cause warming but also cannot maintain warmth when CO2 is high.
Also, experts in ice core analysis indicate that there is 30–50% losses of CO2 during the traumatic micro fracturing during the depressurization of ice core retrieval. If you back calculate, at 40% losses, what the CO2 might have been originally, we get CO2 concentrations the same or much higher than now and quite similar to the direct CO2 chemical bottle data that shows that CO2 has been high during three periods of the last 200 years and as high as 550 ppm (400 ppm at present) (200 years of direct chemical CO2 bottle data by Ernst Beck)
I am glad you posted this. I was questioning the ice core level of CO2 as presented. It only seems logical that CO2 levels were higher than what the ice cores represent for the exact reason you state. A 32 F bottle of coke retains most of the CO2 injected into it, however a warmer bottle will boil over with CO2. The oceans are similar in their retention of CO2. Warmer = less CO2 (or any other gas)
There is no real evidence that CO2 has any effect on climate. It is just conjecture. If greenhouse gases added to global warming then H2O has got to be the culprit. For significant amounts of CO2 to enter the atmosphere, large volumes of water need to warm up. But for H2O all that is needed to wa
rm up is the surface of the water and the air. The claim is that H2O is a positive feedback to the climate effect of increased levels of CO2. But if H2O provides such a positive feedback it must provide a positive feedback to increased levels of itself. Positive feedback systems are inharently unstable yet the Earth’s climate has been inharently stable for at least the past 500 million years, enough for life to evolve. Besides being a greenhouse gas, H2O is a major coolant in the Earth’s atmosphere which is a major reason why the feedback effect of H2O must actually be negative and hence mitigate the effects of other greenhouse gases on climate. If CO2 actually affected climate it would have to do so by changing the radiometric thermal insulation qualities of the atmosphere. The increase in CO2 that has been observed would cause an increase in the natural lapse rate in the troposphere but that has not happened.
It always surprises me these people ignore altitude when discussing icesheet gain and loss. As ice accumulates, surface altitude increases and it gets colder, hence more snow. As ice mass is lost, the reverse happens. Two strong +ve feedbacks.
Stopping the ice accumulation feedback and initiating the ice loss feedback requires a relatively short period of sudden ice loss (and of course other factors have to be conducive, particularly orbital forcings) in perhaps as little as a century or two.
What could cause sudden rapid ice loss over a short period?
My pet theory is that as ice accumulates, sea levels fall and coastal swamps/bogs dry out, becoming susceptible to lightning initiated fires, and we know from current experience, these can burn for decades.
Atmospheric black and organic carbon levels rise and get deposited on the ice, reducing its albedo and initiating melt. Some gets washed off by meitwater, but most doesn’t and over years accumulates on the surface of the ice and is exposed at peak summer melt, causing accelerated ice loss, reducing altitude and reaching the point where other factors can continue the melt, as rising sea levels extinquish the fires.
That’s almost as ridiculous as the CO2 theory.
Here’s how the the Laurentide Ice sheet started as a wee baby 115Ky ago. Cool summers.
http://i58.tinypic.com/izcoi1.png
I hope that graphs right. Huntsville, Al has had a string of 19 days at or above 90F and nine straight days at or above 95F. The extended forecast doesn’t look much better for us.
I only needed to see that the “study” was funded by the National Science Foundation to know what the conclusions would be; so I stopped reading at that point.
hey , i belong to a couple climate change debate sights on facebook. im surely in the minority going up against all these warmists folk and could use some help . if anyone that can debate with some real technical knowledge should join up . this site (wattsupwiththat) is constantly under ridicule and not taken seriously . they have like one or 2 guys that actually study some type of climate science just spewing madness and my technical knowledge can only go so far so any help would be appreciated .i think 1 site is invite only so id have to invite you . get at me at emmdigital at gmail