What are the radiative forcings associated with past Milankovitch cycles?

I don't think you would find such a figure, since such a figure would be disingenuous. Technically the Milankovitch cycle http://en.wikipedia.org/wiki/Milankovitch_cycle

does not change the solar flux (except for the eccentricity portion), http://en.wikipedia.org/wiki/Solar_forcing

the way the atmosphere behaves, http://en.wikipedia.org/wiki/Greenhouse_effect

or the length of the seasons. It only changes the severity of the seasons, http://en.wikipedia.org/wiki/Precession

and thus the extent of glaciation. Calculating the RF based on increased albedo http://en.wikipedia.org/wiki/Albedo

would be a simple calculation based on the Stefan–Boltzmann equation:

Energy Out = KT^4 http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzm...

K = a constant

T = absolute temperature

I suggest you consider the paleotemperatures estimated via ice core data. (About 10 Kelvin temperature change per ice age) http://en.wikipedia.org/wiki/File:Vostok_420ky_4cu...

Assuming an average earth temperature of ~300 Kelvin, the change in output would be:

RF = [K(310^4)]/[K(300^4)] -1 = 14% of the current solar insolation.

The truth is probably different. First, the ice core samples are responding to proxies that respond to temperature changes over time, thus smoothing over the peaks. 10 Kelvins is probably low given the smoothing. Also, not all of the 10 Kelvins are likely to be caused by the Milankovitch cycles. Other cycles and factors are in play, and arbitrarily assigning all 14% to a particular theoretical cause is as pretentious as the IPCC's calculations of the CO2 forcing;

Heat increase = 5.35 ln C/278 http://www.ipcc.ch/publications_and_data/ar4/wg3/e...

C = atmospheric CO2 concentration in ppmv

278 = baseline CO2 concentration in ppmv

and will be met with the same skeptic reaction. The 14% should be considered a low estimate (thanks to smoothing) of an upper limit (thanks to other factors).

For another number, you could calculate the increased albedo due to the increased glaciation.

Glaciers ~ 60% reflection

Not Glaciers ~ 20% reflection

Ocean ~ 8% reflection

Then figure the maximum extension of the ice:

~ 45 degrees North latitude

Edit:

All good points; especially the one about the poles seeing more change.

"your #s confuse forcing with feedback."

Indeed, my point was that such a calculation would be "disingenuous".

@Ben O:

You underestimate him. He is smarter than most Warmists.

The total forcing between inter-glacial and glacial periods appears to be 3.4 Watts per meter squared. This mean current forcing due to anthropogenic greenhouse emissions which estimated to be 1.5 to 2 watts per meter squared will overcome any negative forcing due to milankovitch cycles. In other words, in spite of the fact that the Earth should be heading into another ice age it is not, and as long as humans continue to emit these gases the Earth will never experience another glacial period.

http://www.ossfoundation.us/projects/environment/g...

I do not have the link to papers showing it at this time. The last time I saw it was when reading Dr. Hansen's new book "Storms of my Grandchildren." I will try and look up the reference in the book.

Portland Joe needn't try to tell MTR student that often scientific papers speculate.

As far as believers are concerned, if it's in a peer reviewed article, it's gospel.