why isnt the Milankovich cycles accepted as the cause of climate change on earth?
like it doesn’t seem to be accepted as the first and foremost causing factor of climate change. Why not? If it is accepted as a theory that has cause drastic climate changes such as the glacial periods then why wont it be accepted as creating climate change?
As we are currently at the peak of the Milankovitch cycle i.e, near circular orbit and minimal tilt it would be common sense that the world would be warming naturally from the Maunder Minimum. However, in the IPCC’s own words "a comprehensive mechanistic explanation of these variations remains to be articulated" .The mode of warming through solar forcing and the various feedbacks are not fully understood and hence can not be articulated within the models, so only a simplistic allowance for solar variance is considered.
The IPCC do however accept "minor changes in solar activity can cause dramatic climate shifts" (Bard et al, 2000, IPCC, 2007) and that solar forcing most likely drove the earths natural climate. Hence it is accepted as the primary driver of the earths natural climate, it just can not be modelled yet due to limited understanding of the various processes and feedbacks associated.
Akansofu, 2008, shows that when PDO cycles are accounted for the earth has been warming at a constant 0.5 degrees / 100 years since the Maunder Minimum, long before human produced co2 could have had an effect, and that increased co2 over the last 50 years has not accelerated the warming trend. This study is based on empirical data and common sense rather than climate models. This coincides with increased solar activity as is shown in IPCC AR4 WG1 Chapter 6, of a slightly higher level than that which caused the Medieval Optimum.
Some time over the next few thousands years it is expected that the Millankovitch Cycle will trigger the next ice age, as we are currently at a peak and it can only go down from there!
There is still much uncertainty is this area of climate science and has been identified by the IPCC as an area that requires significent research.
If anyone tells you the IPCC have already accounted for this in their climate models, they have obviously not read the body of the scientific work.
*sigh*
because this time, it isn’t.
"Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6000 years ago will continue for the next 23,000 years."
from;
Modeling the Climatic Response to Orbital Variations
John Imbrie and John Z. Imbrie
http://www.sciencemag.org/cgi/content/abstract/207/4434/943
It’s just a theory among a number of possibilities.
As the Earths orbit becomes more circular, the Northern Hemisphere gets more seasonal variation and the Southern Hemisphere gets less. The average distance from the Earth to the Sun hardly changes so total energy incident on the Earth does not significantly change. There is no certainty that the changing shape of the orbit will cause either cooling or warming.
I think it’s due to them stating they don’t see evidence of that happening now. The factors I see in play now are Sun Spots, the PDO and AMO and all of those point to a cooling period.
PDO = Pacific Decadal Oscillation
AMO = Atlantic Multidecadal Oscillation
Here are the four primary causes/theories. http://www.eoearth.org/article/Causes_of_climate_change
They do have warming and cooling predictions based on orbital and solar cycles. http://en.wikipedia.org/wiki/Solar_variation
Because people can’t be blamed for it. If people can’t be blamed for it, then they have no reason to try and control your behavior.
Milankovitch cycles form a portion of the external effects on climate. But not all of them as there are several hundred known external causes of climate variability and most if not all of them are poorly understood. For instance there is a know geologic interaction with orbital alignments in that we have greater earthquake and volcanic activity during major cosmic alignments that are blamed on gravitational effects. I can see this happening within the solar system but not in the larger universe as many seem to believe.
http://en.wikipedia.org/wiki/Milankovitch_cycles
http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html
What you are looking for is an interaction between Milankovitch cycles and the climate and while recognized it is not well understood because they say these cycles only produce ice ages or interglacial’s like we have been in for about 10,000 years now. What many if not all of those who have bought into the AGW hypotheses do not understand is the large number of potential climate change causes and just how poorly they are understood even by their heroes. Just during this current interglacial we have had 4 very well documented climate optimums preceding the current one all of which were considerably hotter than our present one will ever be and several climate skies at least one of which was much hotter than we are currently. Many of these fluctuations do not match with Milankovitch cycles. So because our science on this is still to primitive to give an exact answer yet as to the cause of these fluctuations they blame Co2 and our technological civilization because they believe it will be hard if not impossible to disprove their hypotheses.
http://nov55.com/ntyg.html
Wander around here a little and find some other theories about geologic and solar effects that we already know are thousands of times more powerful in effect on the climate than Co2 could ever be.
http://mivo-sys.tripod.com/hydro.html
Hydrothermal side effects from geologic activity that can warm oceans releasing Co2 into the air and melting ice in contact with the warmer seas.
http://science.nasa.gov/headlines/y2008/30sep_blankyear.htm
The side effects of sunspots and solar activity on the worlds climate. Point is that there are a lot of powerful effects working on the climate that the AGW believers either refuse to consider or the will not take serious that anything but human technology can alter climate despite thousands of years of historical and scientific studies that prove otherwise. AGW is not now and never will be scientific no matter how much they chant their mantras and try and burn in effigy the heretics like myself that know there are more and better answers out there that need to be found.
Because Global Warming is a trillion dollar industry. Where the global warming crowd was once an impediment to world economies, they are now an integral part of it.
Big E will replace Big Oil in the 21st century; and science, economics, and governments will kneel at its whim.
The Milankovitch Cycles are *a* cause of climate change on Earth, but not the only cause.
We’re also in the middle of a long-term and very gradual cooling portion of the Milankovitch Cycles.
"Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years."
http://www.sciencemag.org/cgi/content/abstract/207/4434/943
And as you can see here, the planet was indeed cooling slowly from about 8,000 years ago until about 100 years ago.
http://globalwarmingart.com/wiki/Image:Holocene_Temperature_Variations_Rev_png
So clearly the Milankovitch Cycles are not causing the current global warming.
It definately should be. it is completely true. The reason it isnt, is because Al Gore and the green party can profit off of the global warming is all our fault plot.