Is the Supermoon responsible for record low Polar ice formation?

The  “Supermoon”  on November 14th coincided with the closest (perigean) approach to the earth of the moon since 1948. Tidal forces are inversely proportional to the cube of distance. Full moon occurs  when the sun lines up with the moon and November 14th is also close to the perigee of the earth’s orbit round the sun. This combined to produce strong tides. At full moon in November the moon lies in the southern hemisphere . So for the Arctic it is the opposite facing tides that is strongest while for the Antarctic it is the direct lunar facing tide that dominates. They are symmetric. Here are my calculations of the tractional acceleration at different latitude covering November, based on the JPL ephemeris.

arctic-amplify

The tractional tidal force acting at 45N (green) and 75N (blue). Polar regions experience far greater tidal ranges during the lunar month than temperate regions. The Supermoon amplified this effect by about 20%. This enhanced tidal mixing and has probably inhibited ice formation since early October.

It is the tidal range that is maximised during a perigean spring tide. That is the difference between low and high tides. At high latitudes this effect is magnified  as just one tide dominates and neap tides effectively disappear completely. This gives an extreme varying monthly tidal range. Tides act throughout the ocean,  dragging both deep  and shallow water alike. This increasing churning tidal flow since October has had two effects. First it has  inhibited natural sea ice formation, and secondly mixed in more warmer water from lower latitudes than normal.  These large tidal ranges look likely to continue till the end of 2016 before returning to normal.

figure2a

The Arctic ocean also has relatively shallow basins with narrow channels at the Bering Sea and to the North Atlantic between Iceland-Scandinavia. This accentuates tidal flow.

Thanks to @Kata_basis for prompting me to look into this !

see also:

  1. Does the moon trigger interglacials
  2. Evidence of  tidal effect on the polar jet stream
  3. Tidal effects in Polar regions
  4. The straw that broke the camels back

 

 

Posted in Climate Change, Ice Ages | Tagged | 5 Comments

Carbon Recycling

The carbon cycle can be rather confusing as there are at least 3 totally separate processes at play, each occurring on different time scales. Here we show that it is just geological processes that result in a ‘long tail’ as the atmosphere recovers from a doubling of CO2. This long tail is very small and has little long term consequences. Glacial variations are much larger.

To understand the carbon cycle means understanding the difference between CO2 residence time and turnover time. The residence time for an individual CO2 molecule emitted by man is only about 5-10 years (C14 measurements). Every CO2 molecule in the atmosphere is rather quickly absorbed either by photosynthesis or by the ocean. However on average most of them are simply replaced by another CO2 molecule entering the atmosphere through evaporation from the ocean or by respiration. The turnover time is the e-folding time needed for a sudden net increase in CO2 to decay back to normal. At equilibrium the total CO2 content of the atmosphere remains constant over decadal time scales. Currently though, as a result of our emissions, slightly more CO2 molecules are being absorbed than are being returned to the atmosphere. The atmosphere is therefore not quite in equilibrium with ‘natural’ life and the oceans.

Estimate of current carbon flows between the atmosphere and the oceans. Figures are in Gtons of carbon. Graph originally from Grid Arendal

Estimates of the current imbalance of carbon flows between the atmosphere and the oceans. All figures are in Gtons of carbon based on a total atmospheric carbon at 750 Gtons (CO2: 390ppm). Plot made by Grid Arendal

If you sum up all the sources and sinks then you find that about half man-made emissions are being absorbed each year. That means that only about half of the CO2 emitted by humans remains in the atmosphere. The strange thing is that this ratio hasn’t changed at all in 50 years, despite rapid increases in emissions.

AR4 plot: The fraction of Anthropogenic CO2 retained in the atmosphere is unchanged in over 50 years, despite increasing emissions.

AR4 plot: The fraction of Anthropogenic CO2 retained in the atmosphere (b) is unchanged in  50 years, despite increasing emissions (a).

Today we are emitting about twice as much carbon dioxide as we did 30 years ago, yet only half of it survives a full year. That means that currently, an amount of carbon dioxide equal to the total annual emissions of 30 years ago is being absorbed each year. Why is this and what does it mean? Part of the answer lies with the greening of the earth, but far more importantly the answer lies in how the oceans are responding.

There is a ‘concentration effect’ acting on ocean sinks due to the increasing partial pressure of CO2 in the atmosphere.  While we are still increasing emissions then levels will continue to rise. If instead we can stabilise emissions at some number of Gtons/year then CO2 levels would also stabilise, albeit at a higher level in the future. If we could cut emissions completely then levels would stabilise at a much lower level over a few hundred years. However, they would still not fall to pre-industrial levels for 100s of thousands of years. This is because of the so-called ‘long tail’ effect. So what exactly is going on and can we estimate what future levels will be?

There are 3 independent Carbon cycles which in total must balance.
1. Dissolution/Absorption of CO2 at  Ocean surfaces.
2. Biological re-cycling of CO2
3. Geological re-cycling of CO2

  1. Dissolution/Absorption of CO2 at  Ocean surfaces.

In stability there is a balance of CO2 Partial Pressures between the surface of the ocean and the atmosphere. At any given temperature the exchange of carbon dioxide molecules between the atmosphere and the ocean surface always reaches an equilibrium. This equilibrium is controlled by the partial pressure of CO2 in the atmosphere equalising to the partial pressure of CO2 in the surface of the ocean. Then the number of carbon dioxide molecules that escape from the sea surface is  balanced by the number that enter the sea from the atmosphere.

If the temperature of the ocean rises then the kinetic energy of the carbon dioxide molecules in the seawater increases and more carbon dioxide molecules will leave the ocean than would enter the ocean. This continues until the partial pressure of carbon dioxide in the atmosphere increases to balance the new pressure at the sea surface.

If instead the ocean were to cool then the reverse of the above would happen, and CO2 levels would fall. Consequently carbon dioxide is more soluble in cold water than in warm water. This is Henry’s law. One consequence of this effect is that the oceans “inhale” carbon dioxide from the atmosphere into cold sea surfaces at high latitudes and “exhale” it from warm sea surfaces at low latitudes.

Increasing the carbon dioxide concentration of the atmosphere therefore causes the oceans to take up (inhale) more carbon dioxide. Because the oceans surface layer mixes slowly with the deep ocean (hundreds of years) the increased carbon dioxide content of the surface ocean will be mixed very slowly into the large carbon reservoir of the deep ocean. The rate of our adding carbon dioxide to the atmosphere is too fast for the deep ocean to be a significant reservoir. So as the carbon dioxide content of the atmosphere rises, so too does the concentration in the ocean surface.

2. Biological cycle of CO2

Cyanobacteria were the first organisms to develop photosynthesis. They evolved 2.5 billion years ago and quickly spread across the oceans, because they depend only on CO2, H2O and sunlight. They absorb CO2 and exhale oxygen. As they died and were fossilised into rocks so the oxygen levels in the atmosphere built up by an amount exactly equal to the organic carbon buried in rocks. Plants and trees depend on chloroplasts for photosynthesis, which evolved from symbiosis with Cyanobacteria. Animals could only  evolve to eat plants and breath once oxygen levels became sufficiently high. Biogenic CO2 from dead organisms, mainly calcium carbonate shells, slowly gets buried over eons into sedimentary rocks, a tiny percentage of which ends up as fossil fuels. Peat deposition in wetlands also buries carbon vegetation which eventually ends up as coal. All these processes removes CO2 from the atmosphere and form the biological component of the geological cycle.

The total mass of living plants and animals and carbon in soil, at any given time represents a temporary store of carbon. This is comparable to the mass of CO2 in the atmosphere. Life thrives in warmer climates with high CO2 levels and suffers during colder more arid glacial periods with  low CO2 levels.

3. Geological cycle.

Carbon dioxide in the atmosphere combines with water to produce weakly acidic rain. This acidic rain reacts with Igneous rocks to produce a set of ions and a weak acid. This is washed through soils down rivers to the sea where they react to produce opaline silicate and calcium carbonate. As a result CO2 is removed from the atmosphere.

carbon-earth

SiO2 and CaCO3 are insoluble and will settle to the ocean floor where they are moved by plate tectonics to subduction zones, carried deep into the Earth and heated converting them back into metamorphic rocks and releasing carbon dioxide. When these rocks and their associated carbon encounter Volcanic eruptions or Mid Ocean vents they return the CO2 to the atmosphere, thus ending the cycle.

The Geological thermostat

The rate of tectonic plate motions set the rate at which CO2 is released from the Earth’s interior to the atmosphere. If release from the earth’s interior exceeds the rate at which CO2 is removed from the ocean by the formation of calcium carbonate shells by oceanic biological processes, then carbon dioxide will accumulate in the atmosphere and visa versa. More CO2 leads to a warmer and wetter world which increases rock weathering, removing CO2 from the atmosphere and cooling down the planet  again.

This process has been proposed as the natural thermostat which  kept the climate habitable for 4 billion years apart from a couple of excursions. It sounds like a good theory, but is it actually true? Why is it that 280ppm seems to be the set point for the thermostat? Just how confident  are climate scientists that they really understand the carbon cycle? Can they, for example, explain why lower levels of CO2 occurred during ice ages? This is what AR5 says on the matter.

AR5: All of the major drivers of the glacial-to-interglacial atmospheric CO2 changes (Figure 6.5) are likely to have already been identified. However, Earth System Models have been unable to reproduce the full magnitude of the glacial-to-interglacial CO2 changes. Significant uncertainties exist in glacial boundary conditions and on some of the primary controls on carbon storage in the ocean and in the land. These uncertainties prevent an unambiguous attribution of individual mechanisms as controllers of the low glacial CO2 concentrations.

So the simple answer is no they don’t really understand the carbon cycle. Nor can they determine why CO2 levels in the atmosphere are naturally so low at <0.03%. A proper understanding of the carbon cycle should at least be able to determine why 280ppm is the natural level for today’s climate. I think this is the fundamental challenge for Carbon Cycle modellers.

Anthropogenic CO2

A stable CO2 level in the atmosphere is achieved once  an equilibrium is reached between the ocean and the atmosphere, and this depends on temperature. Anthropogenic emissions must eventually reach such an equilibrium with the ocean and CO2 levels stop rising. This will result in some DT rise in global temperatures. The rock weathering thermostat presumably would then  kick in to reduce CO2 levels back to ‘normal’ over several 100 thousands of years. However before then we would anyway have entered another series of ice ages with lower CO2 settings. Lets see if we can estimate what will happen in the future.

My Simple Model.

slide1
We take two Carbon reservoirs of mass Y(Ocean) and and mass X(Atmosphere).

We emit 2DX per year into the atmosphere X, of which half is retained and half is absorbed into the Ocean. Now consider a time when atmospheric levels have exactly doubled, after which all emissions stop.

Then Atmosphere partial pressure = 2P(X), where P(X) is initial atmospheric pressure.
Ocean Partial Pressure = P(Y+X), the new pressure of the Ocean with  X more CO2 added

We know that at time zero P(Y) = P(X), and that at equilibrium the partial pressures will again equalise.  So putting in some numbers

Case 1: Using full Ocean (after mixing)

Y= 40,000 GtC while X = 610 GtC  (in 1750)

So P(Y+X) = P(Y)40610/40000 = 1.015 P(Y)

Therefore at equilibrium we find that the final atmospheric pressure will be 285ppm. ( a rise of just 5ppm)

Case 2: Shallow ocean mixing only (fast response)

If instead we consider only the surface mixed zone then we should use Y=1000 GtC. Then the answer would be

P(Y+X) =P(Y)1610/1000 = 1.61 P(Y) = 450 ppm.

All this means is that levels would quickly fall within ~10 years to 450ppm and then drop more slowly  over the next ~300 years to 285ppm.

Fall in atmospheric CO2 levels following a doubling of pre-industrial values. Assumes zero emissions thereafter.

Fall in atmospheric CO2 levels following a doubling of pre-industrial values. Assumes zero emissions thereafter. The gap between the blue curve and the dashed line at pre-industrial levels is the ‘long tail’

This simple calculation is complicated slightly if the  climate also warms by say  3C as a direct result of a doubling of  CO2, but you can allow for that using Henry’s law. Since we are using CO2 levels rather than temperature, Henry’s law actually helps us. Taking a mean ocean temperature value of 13 C the solubility of CO2 actually increases by about 10% as temperatures falls. So levels actually fall slightly faster.

My results totally disagree with the BERN model. The BERN model as described in AR4 predicts instead the following decay.

Bern Model calculation of CO2 levels following a doubling of CO2 in the atmosphere.

Bern Model calculation of CO2 levels following a doubling of CO2 in the atmosphere.

In my opinion the BERN model has a logical flaw. It assumes that a fixed 22% of the Anthropogenic increase in CO2 will remain in the atmosphere for hundreds of thousands of years, waiting for  geological weathering – but why would it?  What possible justification is there to image that  it is a fixed percentage,  independent of amplitude?

To illustrate my point, here is an analogy: Suppose I have a bath full of water with 3 holes in the bottom. The first hole is 10 cm wide, the second is 1cm wide, and the third is 1 micron wide. The water will all empty quickly, mostly through the large hole, some through the small hole and essentially ignore the 1 micron wide hole. However the BERN model says no this is wrong. More than  20% of the excess CO2 will sit around waiting hundreds of thousands of years to pass through the 1 micron hole, while ignoring the option of dissolving in the ocean!

It is only when the partial pressures of carbon dioxide between the atmosphere and the ocean re-balances that a new ‘geological’ balance of CO2 can be reached. That happens rather fast and the net increase is small compared to glacial cycle variations, which as we have seen, climate scientists don’t yet understand.

 

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Milankovitch Insolation study

Summary: The annual insolation of planet earth does not change during Milankovitch cycles. Instead it is the distribution of solar energy with latitude and with season that determines the earth’s climate. The most surprising result of this study is that the latitude gradient of summer insolation seems to determine the onset of glaciations. As a result of this we can predict that the next glaciation would naturally begin in  7000 years time.

I have been looking in detail at how long term orbital changes can affect the distribution of solar energy with latitude and with season. These results are taken from calculations based on Laskar’s  LA2004 orbital solution which covers the last 50 million years and future 10 million years.

  1. Seasonal Variation

First we look at the calculations over 6 million years for  the seasonal monthly changes in daily insolation at 65N.

Daily insolation at 65N for different months over 6 millions.

Figure 1: Daily average insolation calculated at 65N for different months over a 6 million year period. Monthly averages  for all 12 months are plotted.  Jan-June are shown in red, while July-Dec are shown in blue.   The green vertical lines shows the same pattern repetition in the future already occurred  2.8 million years ago.

In general there is a symmetrical 6 monthly seasonal balance about the summer solstice (currently June/July). However, one noticeable additional effect is that the variability in autumn (October) is far greater than that during spring (March). Early polar melt season insolation increases much stronger at high obliquity/eccentricity than it falls at the end of the melt season. Summer months are mostly symmetric about the summer solstice. The future pattern over the next million years has a very similar pattern to that calculated from 2.8 million years ago. Despite large changes in orbital eccentricity and obliquity, the total annually averaged insolation hardly changes at all over 6 million years. This is simply a reflection of Kepler’s 3rd law. High eccentricity brings shorter summers. Orbital effects only change the local distribution of solar energy with latitude and season. The total energy received by earth from the sun each year is essentially constant. It is noticeable that currently the distribution of radiant energy is in a low variability phase caused by a smaller eccentricity modulation than normal. Figure 2 in more detail summer months

65N for April, May, June, July, August,September

Figure 2: 65N for April, May, June, July, August,September

The plot above shows a more detailed look  on how precession works to balance spring insolation against autumn insolation. Note that there  a slight difference in timing depending on the choice of June (May21 – June21) or July (June 21 – July 21). This is due to the precession term changes in summer equinox. For the rest of this study we use the July figures, as do most other authors.

2. Latitude

Next we look at how solar insolation varies with latitude during the peak summer month – July.  The data covering the last 800,000 years of glaciations are shown in Figure 3 below. The insolation values plotted are for 6 different latitudes 90,80,70,60,50 and 40. In addition we show in orange the difference in insolation between the pole (90) and 60N.

Ice Volume is shown in cyan. The top graph shows the latitude dependence for July insolation.

Figure 3: Ice Volume is shown in cyan and the Epica (Antarctic)  temperatures in red. The top graph shows the latitude dependence for July insolation for different latitudes. The greatest spread is between 90 and 60. This 90-60 differential is shown plotted below in orange. The 10k rolling average is shown in red and  follows 41K the obliquity cycle. The blue arrows show coincidences with large and small interglacials whereas the lower blue curves show transient warming events. In general GISP Greenland data show stronger effects correlated with 65N,  but they only cover the last 200k years.

It is well know, and confirmed here,  that major terminations and intermediate ice melt-backs always coincide with maxima insolation. However, when two large maxima occur in quick succession at high eccentricity, the second one has little effect. It would appear that the gap between two peaks must be at least one obliquity cycle of 41,000 years to have a strong effect. This could be related to an albedo like hysteresis effect on growing ice sheets. At the summer equinox the net insolation received each day at the pole is the highest anywhere on earth. This average reduces to a minimum at 60N, but rising into a V-shape increase by 40N. This shape is dependent on  orbital parameters.  Three typical profiles are shown in figure 4.

3 typical insolation latitude profiles

Figure 4:  3 typical insolation latitude  profiles for July

Northern Hemisphere weather is driven by the temperature gradients between mid latitudes and the pole. The data show that the largest gradient(DS) in summer insolation is between the pole and 60N and varies with obliquity and precession. This is shown by the orange curve in figure 3. What is very interesting however is to study not the maxima, but the minima in DS. These minima consistently correspond to strong cooling periods throughout the full 800,000 year period,  corresponding to an  increase in (Benthic Fora) ice volume and a decrease in Epica temperatures. This is shown in figure 5.

Arrows show minima in the gradient of solar heating between 90N and 60N.

Figure 5: Arrows now show minima in the gradient of solar heating between 90N and 60N – (brown signal above)

The data show  that there is always a cooling effect on climate whenever the insolation gradient is minimum at high latitudes in mid summer. Furthermore minima in gradient do not correspond to minima in insolation. Presumably this is because a smaller change in energy flux difference with latitude reduces  mixing of warm air masses from lower latitudes towards the poles. This effect is looked at in more detail in the Figure 6, below which also shows the smaller, but more variable, gradient difference between the Pole and 40N

Detail of last 200,000 years. The lower curve is the S(Pole) - s(40). This shows stronger variability of the same cooling effect.

Figure 6: Detail of last 200,000 years. The lower olive curve is the S(Pole) – s(40) difference. This shows stronger variability of the same cooling effect. The next minima occurs in 7000 years time.

There is good agreement. Minima never occur within an interglacial, except the interesting case 190,000 years ago, coincident with a maximum in polar insolation. The large peak in 65N insolation gets cut short, leading to a rapid fall in temperature and increased glaciation. Assuming these observation are correct, then it is a simple matter to ‘predict’ when the current interglacial will end. Sawtooth interglacials like the Eemian 120,000 years ago and especially the Anglian 400,000 years ago always end  at the next DS gradient minimum. The most recent glaciation is also similar to the Anglian since both ended when the 400,000 year eccentricity modulation was at a minimum. The insolation data can be extrapolated forward to successive minima as shown in figure 6.  The next minima will occur in 7000 years time. Under normal circumstances this minimum  would naturally terminate our present Holocene interglacial, and probably also end  human civilisation. Could global warming delay the next ice age?

Anthropogenic Global Warming is real but its long term effects are still uncertain. The best measure of such effects  is climate sensitivity, or the net warming caused by a doubling of CO2. Despite 30 years of research this value has remained unchanged in the range 1.5 to 4.5C. Why is there no progress despite huge investment? I think the basic problem is that there  is a communal agreement that all climate models are valid. However, that can not really be the case as I described here.  Climate sensitivity must  have an exact value, but scientists are reluctant to give any preference on this, lest it damage funding for rival modelling groups. Therefore I will give my best estimate based on those models that best fit the measured temperature data. The answer is ECS=2.3±0.5C. Warming at this level is serious but not disastrous, since we know that such levels have occurred many times in the past.  CO2 levels must eventually begin to fall within a hundred years from now, because by then we will either have developed alternative energy sources,  or else society will have already collapsed. The biggest question 2000 years from now will be whether global warming has been sufficient to delay the next ice age by 50,000 years.  Assuming we are still in control of our destiny then,  we will likely then be trying to keep CO2 levels artificially elevated.

Updates: thanks to Lance Wallace for correcting spring/autumn mistake.

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