The change in CO2 concentration is pretty easy to see. The obvious always gets the blame. To solve puzzles you have to decide if the answer is a simple joke hidden in a complex picture or if the picture is really complex. The Earth climate system is pretty complex.
In Let's Concentrate on Concentrations I tried to show that there is a small changing in concentration of CO2 that has a rapid initial radiant impact that decreases with time and a slow conductive impact that increases with time. The solar output has daily rapid changes due to rotation, annual changes due to orbit and obliquity of the axial tilt of the Earth, processional changes due to wobble around the axial tilt and finally, changes in geomagnetic intensity that vary with the solar cycle and internal dynamics of the molten core. There are layers upon layers of small changes with differing rates of change. That is a pretty complex system. Missing from the debate is the relative rotation of the complex layers, where the Bucky ball shaped model is helpful.
Imagine standing on the surface and looking up to the tropopause. The surface has a radius R and the tropopause has a radius of 2R. The surface is turning at velocity S and the tropopause is turning at a rate of S/2 for simplicity. Whatever energy the surface gets from the sun is 1/2 what the tropopause gets because of the difference in radius and area of the tropopause relative to you observation point get twice as much because it is moving half as fast. All else being equal, our climate is based on these two layers accumulating energy at different rates, different times and at different relative positions. No big deal right?
Now let's change the sun by a watt. That has 1/4 Watt impact on the surface and 1 Watt impact on the tropopause. Because of the relative velocities of these two layers, there is a large potential difference between the layers that a small change in solar would indicate at first blush.
With the ink in the aquarium experiment, CO2 has more impact on the change near the surface which approaches saturation more quickly than the tropopause. We have yet another impact that differs due to the different relative properties of the two layers.
Now I have to go fishing, but which do you think might be impacted more by a change in geomagnetism and solar magnetism, the surface or the tropopause?
The tropopause may indeed respond to fluctuations in the geomagnetic field. Plus the upper troposphere total energy relative to the surface, which would include the velocity of the jet streams, produces a complex dynamic relationship influence by natural cycles including the solar wind, magnetic orientation as well and TSI fluctuation. This would tend to reinforce Milonkovic cycle theory.
The correlation of climate with solar, including geomagnetic has bee done to death. So the next step is figuring out the magnitude of the geomagnetic impact and proving the limits of CO2 forcing yet again.
The impact of the change in atmospheric conductivity with CO2 increase appears to be a good clue for the scale of change required. Improved thermal conductivity with increased CO2 is small, but much more linear than radiant impact. Since it mainly effects the ocean surface to atmosphere interface in the southern oceans, millennial scale changes in the thermal conductivity approach a balance with other forcing. This would require multidecadal or century scale reductions in solar forcing to increase snow/ice cover to the point where albedo change can continue a cooling trend allowing more absorption and sequestering of carbon dioxide.
The last little ice age, a century scale event, should be typical of an off major cycle cooling response. Major cycles being linked to the Milankovic cycles which would produce millennial or multi-millennial cooling/warming events.
The best estimate I have to date for solar minimum impact is 0.25 Wm-2 at the surface. That would require 4 to 8 times the length of a solar half cycle, approximately 5 years, to trigger a new little ice age. Now I just have to fine tune that estimate to get a rough estimate of how much geomagnetic change may be required, which is not easy for a variety of reasons. Fun, fun, fun.
Enjoy your holidays!