In the last article I showed how the temperature change between Glacial and interglacial was sufficient to cause up to 2.3km of crust to be forced down into the earth’s core. In this article I examine how this could affect climate.
CO2 production from Cement making
A windmill takes energy from the wind and in so doing it opposes its motion. To enable that, each windmills has several hundred tonnes of concrete make from cement which is in turn produced by heating limestone rock.
The breakdown of calcium carbonate from heat is called thermal decomposition and the equations for this thermal decomposition of calcium carbonate are:
This decomposition will occur at depths of around 100km or greater. So, although no ice-age cycle will be sufficient on its own to push crust down this far, the successive expansion and contraction will ratchet the rocket downward so that the rock moves another 2.3km downward toward the point where it decomposes.
Similar processes will occur for most carbon containing rocks so that overall up to 2.3km of the 40,000 km of crust will be pushed down.
Carbon is found throughout the earth but particularly in Marine sediments and rocks as shown by the following table.
What is the effect of this Thermal subduction?
When carbon bearing rock like limestones are heated in the earth’s crust they will give off CO2 and various other chemicals including water. Whilst the crust is not pushed down far at any plate, the net effect of the thermal expansion is to push around a kilometer of rock down which in turn pushes rock that was previous subducted during a previous cycle even further. The net result is that around 1km of rock will be heated to release its carbon and other products.
During the warming phase, the earth’s crust will expand pushing outward. With no where else to go, the rock will be forced down at so called subduction zones. (fig 4.2)
Thus at and after the warming phase from the interglacial we should expect to see an increase in earthquakes as the earth “creaks” much like a house creaks on a hot day as it heats or cools. (fig 4.3)
And whilst the 20th century warming is very short in comparison to the ice-age cycle some studies have shown a linkage:
- Another story about global warming causing volcanoes…
- CO2 causes earthquakes, is there anything it can’t do?
- Guardian: Global warming to trigger “earthquakes, tsunamis, avalanches and volcanic eruptions.”
As I explain above, the surface rock subducted will decompose releasing CO2 and other decomposition products like SO2 and water vapour. (Fig 4.4)
And because it takes time for temperature changes at the surface to penetrate the crust, over time more and more crust is pushed down, eruptions continue until the expansion phase ceases and the remaining oceanic plate is decomposed at which point the eruptions cease.
When the cooling phase sets in, the crust will begin to contract. However, rather than reversing the flow of mantel that has been subducted downward, it is far easier to find a week point of the crust and to pull it apart. Such weak spots exist at mid oceanic ridges such as that running down the centre of the Atlantic. Here the rock will be pulled apart (fig 4.5)
So, the result of the cooling induced by the ice-age will be to increase the (apparent) rate of ocean floor spreading. (Fig 4.6)
Allowing fresh mantel material to fill the gap. (Fig 4.7) Material which does not contain all the volatile components that bubble up near the subduction zones.
And on to the next warming phase.
By filling the gap, the newly extruded crust material now prevents expansion, so that a further warming phase of the ice-age cycle, will have a ratchet effect subducting further material.
In effect, the crust moves like a caterpillar … first thermal expansion pushes material down subduction zones, then them al contraction pulls the tail up so that ice-age cycle by cycle the crust moves rather in the way of a caterpillar.
Evidence for a link between CO2 and ocean crust formation
Because this theory predicts a regular cycle of ocean crust formation corresponding to the ice-age cycle, I have been searching for evidence to support (or refute) this hypothesis. Now at the very last minute comes this from WUWT
The prediction I am making is that ocean floor formation will be a minimum as we leave an ice-age (corresponding to lowest CO2) and then rise after thermal expansion to a maximum. However, whilst the above graph shows a correlation between sea floor formation and ice-age cycle, the sea floor parameter is depth of the sea and the age is an estimate which seems to be based on constant rates of sea floor spreading and the age is based on changes in magnetism through a single period of normal magnetic polarity.
So, whilst this is indicative of a correlation it is unclear but Tolstoy seems to believe it supports this hypothesis:
Sea floor eruption rates, and mantle melting fuelling eruptions, may be influenced by sea-level and crustal loading cycles at scales from fortnightly to 100 kyr. An ~100kyr periodicity in fast-spreading sea floor bathymetry, and relatively low present-day eruption rates, at a time of high sea-level and decreasing orbital eccentricity suggest a longer term sensitivity to sea-level and orbital variations associated with Milankovitch cycles. Sea floor spreading is considered a small but steady contributor of CO2 to climate cycles on the 100 kyr time scale, however this assumes a consistent short-term eruption rate. Pulsing of sea floor volcanic activity may feed back into climate cycles, possibly contributing to glacial/inter-glacial cycles, the abrupt end of ice ages, and dominance of the 100 kyr cycle.
[Note: when I wrote this, I was expecting to use CO2 in a novel way to drive the climate. As I said in I’m now a CO2 denier, this approach ran into problems when I found CO2 and climate are not correlated during the cooling phase of the ice-age cycle. However, just as CO2 is released so other decomposition products will be released by this volcanic activity many of which are active in the climate. So the basic premise that the 100,000 year time delay for climate causing the ice-age cycle still has merit even if CO2 might not be the key ingredient being released]
Estimate of CO2 released
if we look at the amount of Carbon in the various constituents of the earth we find:
Amount in Billions of Metric Tons
578 (as of 1700) – 766 (as of 1999)
|Soil Organic Matter||
1500 to 1600
38,000 to 40,000
|Marine Sediments and Sedimentary Rocks||
66,000,000 to 100,000,000
540 to 610
|Fossil Fuel Deposits||
Table 4.1 Source: Forest Hydrology: An introduction to Water and Forests
As we showed above, the expansion of the earth’s crust over an ice-age cycle at the surface is around 2.3km at the surface over 40,000km. Thus on average, the fraction of rock that would be forced down is given by:
Fraction of crust subducted x quantity of carbon in rocks.
= 2.3/40,000 x 100,000,000 billion tonnes
=6 x 1012
This means that if the subduction depending on the surface expansion, up to 6 x 1012 tonnes of Carbon would be released as a result of thermal expansion induced subuction after an ice-age. This is equivalent when released as CO2 to around 20,0o0 billion tonnes of CO2. In comparison:
Since 1750 humanity has added 520 billion metric tons of greenhouse gases to the atmosphere and we’re on pace to add that much again within 40 years
Even if we take the expansion at 2.3km down where the effect of the cooling takes longer to impact and so is smaller, the total CO2 released is the same as all the CO2 released by humanity so far.
CO2 isn’t the only game in town
However, whilst we have measurements of CO2, we must not forget that CO2 is not the only climate driver from volcano activity. Sulphur dioxide, particles and water vapour could all play their part.
This suggests that each glacial cycle will create around
2.3 x 100,000,000 / 40,000 billion tonnes of carbon in rocks
=6 x 1012 tonnes of carbon
=2 x 1013 tonnes of CO2
So, thermal expansion of the earth’s crust and subsequent decomposition of rock to release CO2 or some other components appears to have the magnitude of impact that might cause or trigger climate change and it occurs on roughly the time scale we require.
But even though masses of CO2 are released, it cannot on its own cause this change.
[Note: when I wrote this, I was expecting to use CO2 in a novel way to drive the climate. As I said in I’m now a CO2 denier, this approach ran into problems when I found ghat the level of CO2 is not correlated with temperature during the cooling phase of the ice-age cycle. There is a critical dip in temperature around 16,000 years after the inter-glacial peak without the necessary similar sized corresponding dip in CO2. So CO2 cannot be either directly responsible or causal via any linear feedback mechanism.
However, just as CO2 is released so other decomposition products will be released by this volcanic activity many of which are active in the climate. So the basic premise that the 100,000 year time delay for climate causing the ice-age cycle still has merit even if CO2 might not be the key or only ingredient being released]