A paper published today in Geophysical Research Letters finds Arctic sea ice extent is determined primarily by the natural ~60-90 year cycle of the Atlantic Multidecadal Oscillation [AMO], not greenhouse gases.
According to the authors, "Arctic sea ice is intrinsically linked to Atlantic multidecadal [natural] variability" finding a ~60-90 year cycle of "Covariability between sea ice and Atlantic multidecadal variability as represented by the Atlantic Multidecadal Oscillation (AMO) index is evident during the instrumental record."
The paper adds to many other peer-reviewed publications finding changes in Arctic sea ice are primarily related to natural variability of ocean and atmospheric oscillations, storm and wind activity, and not changes in greenhouse gases.
A Signal of Persistent Atlantic Multidecadal Variability in Arctic Sea Ice
Martin W. Miles et al
According to the authors, "Arctic sea ice is intrinsically linked to Atlantic multidecadal [natural] variability" finding a ~60-90 year cycle of "Covariability between sea ice and Atlantic multidecadal variability as represented by the Atlantic Multidecadal Oscillation (AMO) index is evident during the instrumental record."
The paper adds to many other peer-reviewed publications finding changes in Arctic sea ice are primarily related to natural variability of ocean and atmospheric oscillations, storm and wind activity, and not changes in greenhouse gases.
A Signal of Persistent Atlantic Multidecadal Variability in Arctic Sea Ice
Martin W. Miles et al
Satellite data suggest an Arctic sea ice–climate system in rapid transformation, yet its long-term natural modes of variability are poorly known. Here, we integrate and synthesize a set of multi-century historical records of Atlantic Arctic sea ice, supplemented with high-resolution paleo proxy records, each reflecting primarily winter/spring sea ice conditions. We establish a signal of pervasive and persistent multidecadal (~60–90 year) fluctuations that is most pronounced in the Greenland Sea, and weakens further away. Covariability between sea ice and Atlantic multidecadal variability as represented by the Atlantic Multidecadal Oscillation (AMO) index is evident during the instrumental record, including an abrupt change at the onset of the early 20th century warming (ETCW). Similar covariability through previous centuries is evident from comparison of the longest historical sea ice records and paleo proxy reconstructions of sea ice and the AMO. This observational evidence supports recent modelling studies that have suggested that Arctic sea ice is intrinsically linked to Atlantic multidecadal [natural] variability. This may have implications for understanding the recent negative trend in Arctic winter sea ice extent, although because the losses have been greater in summer, other processes and feedbacks are also important.
Arctic sea ice controlled by NAO
ReplyDeletehttp://www.klimatupplysningen.se/2013/11/20/nya-ron-fran-kalkalger-i-arktis/
But if this is so, then why didn't the Northwest Passage and Northern Sea Route didn't both open up about 5-6 times in a row 60-90 years ago? Is that too far away from the Greenland Sea? And how how about the ice shelves north of Ellesmere Island that were there for thousands of years, but have now almost completely disintegrated?
ReplyDeleteThis is something I don't understand if it's all just a cycle...
read some of these posts
Deletehttp://stevengoddard.wordpress.com/?s=navigate
http://hockeyschtick.blogspot.com/search?q=arctic+sea+ice+less
I read some of those posts, but my questions do not seem to get answered there. For instance, we know what caused summer Arctic sea ice to be low during the Holocene Climatic Optimum, but that cause is not applicable to today's situation.
DeleteCan you point me to a blog post here or at Goddard's that explains my question: Why didn't the Northwest Passage and Northern Sea Route both open up about 5-6 times in a row 60-90 years ago? Is that too far away from the Greenland Sea? And how how about the ice shelves north of Ellesmere Island that were there for thousands of years, but have now almost completely disintegrated?
"other processes and feedbacks are also important."
What could those processes and feedbacks be? Shall I try to get a hold of the paper to see if they are named?
This seems to me to involve as much the philosophy as the substance of science.
DeleteWe do not observe natural sinusoidal cycles with fixed periods. We apply Fourier analysis to long time intervals, say hundreds or thousands of years and DERIVE average periods.
However, we may not be able to drive the logic in reverse to use the general to predict the particular. Partly this is because we do not have a physical model (physics model), merely a mathematical / statistical model.
What we observe as cycles may be chaotic and pseudo-periodic. The methodology cannot distinguish between pseudo-periodic and true periodic phenomena.
[This problem also arises in using the pseudo-periodic stock market cycles to predict the Dow Jones Industrial Average.]
The uniformitarian model proposed by Lyell and others helped to establish natural forces as determinants of Earth's evolution in opposition to catastrophism based on the Biblical story of Noah's Flood. But we now know that so many physical forces change the Earth that it is difficult to distinguish systematic processes from chaotic processes. We may know what causes earthquakes, but we cannot predict a particular earthquake nor say why a particular earthquake occurred when it did.
Today we accept catastrophes as significant determinant sof Earth history. We accept as a possible explanation for the end of the Cretaceous period 65 million years ago that a large bolide struck the Earth.
The same is true when we.examine the paleoclimatic evidence in ice cores from Greenland and Antarctica or the rock samples from the deep-sea drilling program.
We observe evidence to support the Milankovitch Cycle theory from these drilling programs. This theory links the cycles of the Ice Ages to cycles of celestial mechanics.
Yet there is still uncertainty concerning Marine Isotope Stage (MIS) 11, about 400,000 years ago when the inter-glacial period was about 50,000 years long compared to the usual 20,000 years. If there is a 400,000-year cycle [and I believe the evidence is convincing] will the Holocene last 50,000 years? If so, will sea level eventually rise 20 meters?
From what I have read of André Berger's work, that is the most likely scenario. MIS 11 seems to me our best analog for the Holocene. However, I am not certain. The entire Milankovitch Theory may be based on misinterpretation of pseudo-cycles.
J.S. Gould wrote Time's Arrow, Time's Cycle, a history of geology focusing on the conceptualization of Deep Time and uniformitarianism. As I recall he explained why Earth's history cannot.run in reverse.
In my opinion, his explanation also explains why we cannot explain a specific "cyclical" event of the past.
In my opinion a scientist can still maintain that physical determinacy operates at the macro level based on a method that may have been taught by Enrico Fermi.
Legend has it that Fermi taught his students that when presented with a complex multivariate physical system the should estimate on the back of an envelope the effects of as many parameters as possible and then put the estimate away in a drawer while they spend the next few years doing the experiments. Later when they had conducted the experiments they should compare the result to the back-of-the-envelope estimate. They would be astounded how close was their "guestimate".
The moral of this story is that even if a multivariate system looks chaotic, it is probably a deterministic system. What appears to be chaos arises from not understanding all the deterministic processes that produced the catastrophic phenomena. So the pseudo-cycles may be real cycles, except we do not have enough knowledge or understanding of the deterministic processes to explain all the wiggles (components of the sinusoidal pattern).
A philosopher of science might say that there is no way of knowing whether Earth's history follows a chaotic path (arrow) or is governed by physical laws (cycles).