From John Ray's shorter notes
January 16, 2016
Are high CO2 levels preventing a new ice age?
That is what the article abstracted below finds from their modelling. You can read here the amusing gyrations the authors and other Warmists go through in order to claim that we should still worry about global warming. But it follows that if we DID cut CO2 levels drastically that would bring on an ice age. How does the precautionary principle handle that?
What their modelling told them was that we just missed the beginning of a new ice age a couple of hundred years ago -- which is plausible. The current interglacial is already rather long compared to previous interglacials. And they attribute that near miss to levels of CO2 that were unusually high at that time. But note: The levels at that stage were NATURAL. The near miss was before there was any significant industrial civilization. So the claim that CO2 levels in recent times can be naturally high must rattle a few cages. Perhaps your SUV is NOT responsible for the present high levels of CO2!
But how good are their models? They claim to have backcast fairly well but that is a slender reed to lean on. A lot of nicely backcasting models have made a real hash of predicting our present temperature.
The big faults I see in their models are that they accept two conventional views: That the climate sensitivity to CO2 is substantial and that the long term Holocene atmospheric CO2 level was 280ppm. And model outcomes are of course very sensitive to the parameters used. So if either of those assumptions is wrong, all the model outcomes are wrong too.
And skeptics do of course challenge the first assumption -- so if we are right, Schellnhuber & co are wrong. But let's be charitable and give the repulsive Schellnhuber his preferred sensitivity figure.
Papal adviser Schellnhuber
That brings us to the second assumption -- which is probably wrong too. Measuring the deep past through ice cores is a very shaky enterprise, which almost certainly takes insufficient account of compression effects. The apparently stable CO2 level of 280ppm could in fact be entirely an artifact of compression at the deeper levels of the ice cores. Dr Zbigniew Jaworowski's criticisms of the assumed reliability of ice core measurements are of course well known. And he studied them for over 30 years.
So in the end I think this study is a fairly improbable bit of speculation. Fun though!
Critical insolation–CO2 relation for diagnosing past and future glacial inception
A. Ganopolski, R. Winkelmann & H. J. Schellnhuber
The past rapid growth of Northern Hemisphere continental ice sheets, which terminated warm and stable climate periods, is generally attributed to reduced summer insolation in boreal latitudes1, 2, 3. Yet such summer insolation is near to its minimum at present4, and there are no signs of a new ice age5. This challenges our understanding of the mechanisms driving glacial cycles and our ability to predict the next glacial inception6. Here we propose a critical functional relationship between boreal summer insolation and global carbon dioxide (CO2) concentration, which explains the beginning of the past eight glacial cycles and might anticipate future periods of glacial inception. Using an ensemble of simulations generated by an Earth system model of intermediate complexity constrained by palaeoclimatic data, we suggest that glacial inception was narrowly missed before the beginning of the Industrial Revolution. The missed inception can be accounted for by the combined effect of relatively high late-Holocene CO2 concentrations and the low orbital eccentricity of the Earth7. Additionally, our analysis suggests that even in the absence of human perturbations no substantial build-up of ice sheets would occur within the next several thousand years and that the current interglacial would probably last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at least 100,000 years8, 9. Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time.
Nature 529, 200–203 (14 January 2016) doi:10.1038/nature16494
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