Ellis sent me his paper “Modulation of Ice-ages via Precession and Dust-Albedo Feedbacks” in Geoscience Frontiers, and I found it rather intriguing. To greatly simplify: CO2 is good for you, and it’s going to get real cold not too long from now. I asked him to write a summary, which is below, but use the paper for any intelligent criticisms.
Here is an interesting conundrum: climate scientists will claim that the science underpinning terrestrial climate is settled. And yet we can simultaneously discover that there is no clear explanation as to why the climatic changes during ice-ages occur. It is speculated that orbital cycles and CO2 are involved, but it has never been explained why some of these orbital cycles produce ice-ages and interglacials, while others do nothing at all. So why would a climate system be selective in its response to orbital cycles?
The four orbital cycles involved in paleoclimatology are: axial precession, apsidal precession, axial obliquity and orbital eccentricity. And these combine to change the amount of sunlight (insolation) impinging upon the Earth’s higher latitudes. This orbital-induced oscillation is known as the Milankovitch Cycle (singular), which has a periodicity of about 22 kyr, and the changes in sunlight in higher latitudes it induces can be quite large.
Fig 1 shows the Milankovitch Cycle in blue, while the higher latitude temperature response is in red. As can be seen, some of the peaks in the blue Milankovitch Cycle (i.e.: extra sunlight-insolation in high latitudes), produce no temperature response whatsoever. Which is odd, and not explainable by the CO2 feedback theory.
Fig 1. Graph of Milankovitch Cycles (blue) vs Antarctic temperatures (red). Each blue peak represents increased sunlight-insolation in the high latitude northern hemisphere. Each red peak represents an interglacial warming event, which occur roughly every 80 or 100 kyr. Note that some sunlight-insolation peaks produce no temperature response at all. Sources: Laskar 2004 orbital cycles, and Epica3 ice core temperature data.
In fact, the problems with ice age feedbacks and modulation are manifold. There is also the problem that during ice ages, high CO2 is coincident with cooling, while low CO2 is coincident with warming. Which is a highly contrarian response for the standard CO2 feedback theory. Plus all of the interglacial warming events are coincident with northern hemisphere Milankovitch Cycles, rather than the southern hemisphere equivalents.
Again this would be an unusual hemispherically asymmetric response for a global feedback like CO2. And lastly, CO2 is a very weak feedback indeed during interglacial warming, when calculated annually or decadally; while the true feedback needs to be fairly powerful, in order to melt the vast ice northern sheets in just 5,000 years.
The result of this short analysis is that CO2 cannot be the feedback system assisting the Milankovitch Cycle, and thus controlling interglacial modulation. Yet we know that there must be a feedback mechanism of some kind, to explain the missing interglacials (the intermittent temperature response to increased high latitude sunlight-insolation). So the requirements of this proposed novel feedback system are peculiar, because: it must be based in the northern hemisphere; it must warm when CO2 is low; it must be very strong; and yet it has to be intermittent – only operating once every 80 or 100 kyr. And that is a very strange feedback mechanism indeed.
So can we find such a peculiar, strong, intermittent feedback mechanism? A mechanism that has gone unnoticed within climate science for decades?
The intriguing answer, as is discussed and fully explained in my paleoclimate paper, is dust. Yes, humble dust falling on ice sheets and darkening their surface – or ‘reducing their albedo’, in scientific parlance. Fresh snow on polar ice sheets can have a very high albedo, reflecting up to 90% of inbound sunlight back into space, and this can have a huge regional cooling effect on the climate. This explains the missing interglacial problem, because this highly reflective ice can reject so much insolation that some of the Milankovitch Cycles do nothing at all, as can be seen in Fig 1.
While high albedo is a promising start in this quest, our humble dust can similarly explain all of the other peculiarities required by our hypothetical new feedback agent. Dust is indeed based in the northern hemisphere, because it has been determined that Greenland dust is from the high Gobi plateau. Dust can have a very strong warming influence upon ice sheet, increasing sunlight absorption by up to 215 W/m^2, or 50% of the total average sunlight available.
And finally, the dust found in polar ice cores is indeed intermittent, only occurring every 80 or 100 kyr, just before each interglacial warming period. See the dramatic correlation between dust and CO2 in Fig 2. Remember that CO2 is also proportional to temperature, so that dust correlates well with temperature too.
Fig 2. A graph of CO2 (blue) vs Dust (green). Note the good correlation between CO2 and dust (and therefore temperature and dust). Note that the dust-plot is inverted and logarithmic. Source: Epica3 2007 ice core data.
In which case, we may have discovered the true ice-age temperature feedback agent and mechanism – it is dusty-ice-sheet albedo rather than CO2. However, why would dust exhibit this strange intermittency, only arriving in vast dust clouds every 80 or 100 kyr? And arriving, I might remind readers, just before each interglacial warming period.
For the answer to this climate conundrum we must look well outside the suffocating constraints of standard climate science, and remind ourselves that CO2 is plant-food, and thus the most essential gas in the atmosphere. Without CO2, all life on Earth would perish.
But due to oceanic cooling during ice ages, and therefore oceanic absorption of CO2, atmospheric concentrations of CO2 are drawn down during the ice age and eventually reach as low as 180 ppm. This is dangerously low for much of the world’s plant life, especially at higher altitudes where concentrations can reach the equivalent of 150 ppm at the surface. And 150 ppm lies well inside the death-zone for most C3 plant-life.
The result of this low CO2 is that the high altitude Gobi Plateau turns into a CO2 desert. This is a new type of desert caused by a lack of CO2 rather than a lack of rain – a phenomena that goes largely unremarked in climate science. The surface dust from this vast and new shifting-sand desert is whisked eastwards by strong prevailing winds, forming the dusty Loess Plateau in China and also coating the Laurentide and Eurasian ice sheets in dust. And since these new CO2 deserts are caused by cold oceans at the depth of an ice age, these mostly northern hemisphere dust storms can only occur at the glacial maximum.
In other words, these dust storms are intermittent, occurring just before each interglacial warm period. And that relationship is causal, rather than coincidental. It is the dust that is lowering ice sheet albedo, allowing more sunlight absorption, resulting in melting ice sheets and interglacial warming. We are in just such a warm period now – the Holocene interglacial – and we are due another ice age in 500 to 1,000 years. Although the initiating orbital cycles are weak at present, due to low eccentricity, and so it is uncertain if the current orbital cooling cycle will be strong enough to generate a full-blown ice age.
Thus the delightful conclusion to this study, is that during ice-ages it is low atmospheric CO2 concentrations that cause global warming.
Fig 3. A summary graph of all the factors that play a role in glacial modulation.
- Ice sheets (light blue and grey) grow, forcing temperature (red) to fall.
- CO2 (yellow) reduces with temperature (red), due to oceanic absorption.
- As CO2 reaches 180 ppm there are CO2 deserts and dust storms (purple).
- When the next orbital cycle (blue sine wave) comes along, the dusty-ice sheets can melt and the world warms (red peaks).
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