. Crowley and Berner due allow that the complexities of climate modeling may possibly provide an explanation of Veizer et al.'s results, which indicated that CO2 was not a strong influence on long-term climate patterns. This explanation is only deemed necessary IF Veizer et al.'s results are confirmed by "further scrutiny", which has not yet taken place.
To the contrary, the direct radiative forcing of CO2 is very much limited by Stefan-Boltzmann as previously shown ~0.2-0.3oC per doubling and this alone would invalidates a reliance on changing CO2 concentrations as a major causative factor of iceages whether inducing one or ending such.
Changes in aldebo from melting ice today can no more be placed at the doorstep of anthropogenic CO2 change than temperature across time due to other factors.
As can be clearly seen in the above graphic, the Temperature transitions clearly lead the CO2 concentrations. That along with the mininmal direct radiative forcing of CO2 in comparison with other factors, ( water vapor concentration 95% of greenhouse effect, ice pack extent, clouds, etc.)
see also: Origin of the 100 kyr Glacial Cycle
by Richard A. Muller
Whenever ice is heated above 0oC (even from constant solar irradiation and no other factor) it's going to melt, as it melts the extent of the icepack decreases with albedo decreasing as a consequence providing more heating. CO2 is not even a sufficient much less a necessary factor to the event of warming, as historically the surface Temperature leads CO2 concentration as you have noted yourself. Changes in water vapor add even more significantly as one advances out of colder climes of an ice age.
What must be determined is the initator of such warming & cooling events, and changes in CO2 concentration simply does not qualify for lagging in time as well as lack as an IR active substance in comparison with even very small concentrations of water vapor, coupled with the effect of high altitude ice clouds from Solar, interplanetary, and inter galactic events modifying albedo.
To the contrary, the direct radiative forcing of CO2 is very much limited by Stefan-Boltzmann as previously shown ~0.2-0.3oC per doubling and this alone would invalidates a reliance on changing CO2 concentrations as a major causative factor of ice ages whether inducing one or ending such.Now we're talking about two different things. A major glacial epoch is not the same as a glacial period (when the contrasting period is an interglacial). It would be helpful if you could see the Crowley and Berner figure, but I can explain it pretty easily. The whole Pleistocene period of glacial-interglacial oscillations counts to Berner as a glacial epoch, a period in which continental ice sheets were present. His Phanerozoic climate model doesn't have the time resolution capability of distinguishing glacial advance and retreat and the causes of them. I.e., the concentration of CO2 in the atmosphere, in concert with the global tectonic setting (meaning the continental arrangement, the presence, location, and height of mountain ranges) is the main determinant of global climate over periods of millions of years.
Other factors, particularly astronomical factors (though I did read a VERY recent paper by oceanographer Carl Wunsch that addresses Milankovitch forcing factors; he indicates that their influence should be much less than as has been promoted and understood, but the statistics are way, way beyond me) will determine climate change and global temperature over periods that are considerably less than "millions of years". It's obvious from the graph that we've shared that atmospheric CO2 concentration responds to these other factors. Did you notice that Hansen said, as I have said many times, that in this case CO2 acts as a "a positive feedback that contributes to the large magnitude of the climate swings"? Note that this means CO2 and other GHG concentrations act to magnify change in both directions, meaning increasing or decreasing global temperature, because of their radiative forcing effects! To whit, when global temperatures decrease, CO2 and other GHG concentrations decrease, which amplifies (perhaps even accelerates) the climate trend.
Changes in aldebo from melting ice today can no more be placed at the doorstep of anthropogenic CO2 change than temperature across time due to other factors.
That's disputable but not provable. Many of the scientists who have observed the loss of perennial Arctic sea ice have taken pains to make sure that they don't say that the melting ice is a direct consequence of global warming, i.e., GHG-induced climate change or global temperature increase. At the same time, they attribute the melting ice to the observed general warming over the Arctic, which has occurred in the same timeframe (obviously) as the global temperature trend. What I was trying to point out was that the radiative forcing due to ice loss is the same positive forcing factor that is found in Hansen's figure. So no matter what the cause of the melting Arctic ice, the result is a positive radiative forcing term.
What must be determined is the initiator of such warming & cooling events, and changes in CO2 concentration simply does not qualify for lagging in time as well as lack as an IR active substance in comparison with even very small concentrations of water vapor, coupled with the effect of high altitude ice clouds from Solar, interplanetary, and inter galactic events modifying albedo.
Here you state a vital point of convergence in our discussion. Yes, CO2 does not qualify as the initiator of warming and cooling events in the recent (420,000 year, or Pleistocene glacial period) paleoclimate record. I totally agree. Let me reemphasize: I totally agree. But what I have been pushing very strongly in our discussion is the fact that CO2 is a radiative forcing component of Earth's climate system. Increasing atmospheric CO2 concentrations (and the concentrations of other GHGs) should lead to increasing global temperature. The remarkable case of the Paleocene-Eocene Thermal Maximum seems to demonstrate an event in which most other climate components were stable (~unchanging), so that the only change was a rather dramatic increase in CH4 and then CO2 atmospheric concentrations, leading to an apparent large increase in global temperature. (Note also that this event was about 150,000 years long, not 200, leaving the question of how rapidly the climate would respond to this increase wide open -- and that's a very significant question.)
And then the bottom line is: since the mid-1800s, atmospheric CO2 concentrations have increased about 80 ppmv, and they will not stop increasing for decades. There are very few other radiative forcing changes happening in the Earth's climate system right now, though if the Sun launches a few more giant solar flares at us during what is supposedly the down phase of the solar cycle, I might have to change that statement. In the absence of other factors, the rapid increase in atmospheric CO2 concentrations, and the radiative forcing that results from that process, will have an effect on Earth's climate system. Since there is still considerable uncertainty about the magnitude of some negative forcings (particularly clouds), the net result of the GHG forcing is still quite uncertain. Hansen has stated that controlling black soot emissions would do much more than Kyoto x 10, and that technological advance can significantly slow the growth rate of CO2 in the atmosphere. Taken together, that would result in much less forcing than a "no change in current trends" scenario. I think he's right; I've said that before.
That's a lot to say. If there is any justification in calling "global warming" a "global warming hoax", it lies with the media that promote worst-case dire scenarios as if they were as plausible as the midrange, average, mean predictions. Obviously they aren't, but the headlines are more strident. Factually, atmospheric CO2 concentration is increasing, as are the concentrations of other GHGs, though I believe methane has hit a plateau for unexplained reasons. Increasing atmospheric CO2 concentrations are a positive radiative forcing factor. Increased radiative forcing is expected to have a noticeable effect on global climate.
The last three statements are straightforward, factual, and no hoax. Saying otherwise is not contributing to the effort to understand how Earth's climate responds to forcing factors, be they radiative or something else.