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Increase In Earth's Temperature, What Is The Reason?


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Hi, inductance.

 

Good thinking, but, it seems to me that you were overlooked one more subject: satellites are measuring direct thermal radiation from surface, and their data are pretty much matching ground stations.

https://en.wikipedia.org/wiki/File:Satellite_Temperatures.png

 

Overlooked, no. 

 

Satellites attempt to measure the entire lower troposphere which is a 10km layer, so it's a different measurement.

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You're right. But clearly they are match, while stratosphere shows cooling. So it is consistent with greenhouse gasses model.

 

 

According to theory, the lower trop should be warming at double the rate of surface, so one or both are not satisfactorily accurate. 

Also, there's still the missing hotspot above the tropics and a low level of understanding of lapse rate feedback. The science is clearly incomplete. 

 

Btw, the much maligned Willie Soon presented quite a compelling argument for error in the land measurements when he separated rural from urban and semi-urban sites and presented the 2 global trends independently. I might be wrong but I'm one of many who are of the view that the datasets have not been subjected to a desired level of rigorous testing. 

 

Not only is it likely that UHI hasn't been accurately identified, in addition to the potential errors outlined in my first post there's also the issue of sensors themselves, as weather stations around the world are converted from MIG to semiconductor, and recording is automated.

 

Due to the much lower mass of a semiconductor sensor, it's able to measure something closer to a real Tmax, and given that all records are based on Tmax and Tmin, the importance of this cannot be overstated.

 

That said, there's no doubt that the globe is warming and there's little doubt that the observed relationship between temperature rise and human population & CO2 emissions is purely a coincidence, but beyond that there remains important questions that lack reasonable and confident answers.

 

It's therefore not surprising that many scientists say that mitigation action is a matter of risk assessment. We should act, just in case....

 

It's an acknowledgement of the level of uncertainty that exists in reality. 

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The elephant in the room is the fact that the earth naturally goes through cycles of glacial and interglacial periods, and we are still coming out of the last glacial period. It is going to get warmer in the future, with or without us. No doubt, our activities have accelerated this latest peaking towards the inter-glacial, but going by the history of the planet, it would happen anyway.

 

The explanation that I find the most compelling for the cycling climate is the one given by Milankovitch.

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The elephant in the room is the fact that the earth naturally goes through cycles of glacial and interglacial periods, and we are still coming out of the last glacial period. It is going to get warmer in the future, with or without us. No doubt, our activities have accelerated this latest peaking towards the inter-glacial, but going by the history of the planet, it would happen anyway.

 

I thought we had already stopped the "warming" part of the Milankovitch cycle.  We should have been cooling for thousands of years now, according to the pattern.  But since, "No doubt, our activities have accelerated" our emissions, we are now overpowering the cycle.  Now, at our spot in the cycle, orbital forcing will no longer have that cooling effect; but as you can see, it will now also contribute some additional warming force.

 

500px-SummerSolstice65N-future.png

 

The explanation that I find the most compelling for the cycling climate is the one given by Milankovitch.

 

Surely, Milankovitch explains the orbital effects on solar insolation (especially at 65 degrees N. latitude, which correlates best with the glacial/interglacial cycles), but the cycling of climate is affected by other forcers too.

 

A more compelling explanation to many, increasingly, is the one given by Ruddiman

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I thought we had already stopped the "warming" part of the Milankovitch cycle.  We should have been cooling for thousands of years now, according to the pattern.  But since, "No doubt, our activities have accelerated" our emissions, we are now overpowering the cycle.  Now, at our spot in the cycle, orbital forcing will no longer have that cooling effect; but as you can see, it will now also contribute some additional warming force.

 

500px-SummerSolstice65N-future.png

 

 

Surely, Milankovitch explains the orbital effects on solar insolation (especially at 65 degrees N. latitude, which correlates best with the glacial/interglacial cycles), but the cycling of climate is affected by other forcers too.

 

A more compelling explanation to many, increasingly, is the one given by Ruddiman

 As I understand the Milankovitch hypothesis, there isn't one cycle, but several and when they converge the planet experiences the climate extremes of glaciation or inter-glacial periods.

I agree there are other factors as well, chief among those is the cyclic energy storage in the oceans.

I didn't find Ruddiman's hypothesis very compelling but I will have another look at it. Thanks for the link.

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 As I understand the Milankovitch hypothesis, there isn't one cycle, but several and when they converge the planet experiences the climate extremes of glaciation or inter-glacial periods.

 

That graph posted above, of insolation at 65 N., is a composite of the 3 Milankovitch cycles showing the cumulative effect of the 3 cycles.

 

 

 

I agree there are other factors as well, chief among those is the cyclic energy storage in the oceans.

I didn't find Ruddiman's hypothesis very compelling but I will have another look at it. Thanks for the link.

There are probably many cyclic energy storage mechanisms on the planet, though few so large, but that's not the point.

The point should be about the long-term average or "mean" of those cycles, and if that average is being changed or shifted, radically and rapidly.

 

But about the Ruddiman link from above, you might have noticed they kept talking about sparse populations during the Copper and Bronze Ages, with the caveat that people used more land per person back in those days, so therefore Ruddiman's hypothesis would be more plausible.  I think that is probably valid, but also recent research is showing that populations were, at least periodically, also much larger back in those days, from SE Asia to the Americas as well as across Africa.

 

The 2006 book, "1491: New Revelations of the Americas Before Columbus" explains some of that perspective for the Americas.  The more we learn about those early days of civilization, the more sense Ruddiman's idea seems to make.

 

 

...doesn't it?

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Undeniably there are problems with the Milankovitch theory, but there are also proposed solutions.

I will just go the easy route and quote Wiki:

 

The 100,000-year problem ("100 ky problem", "100 ka problem") of the Milankovitch theory of orbital forcing refers to a discrepancy between the reconstructed geologic temperature record and the reconstructed amount of incoming solar radiation, or insolation over the past 800,000 years.[1] Due to variations in the Earth's orbit, the amount of insolation varies with periods of around 21,000, 40,000, 100,000, and 400,000 years (Milankovitch cycles). Variations in the amount of incident solar energy drive changes in the climate of the Earth, and are recognised as a key factor in the timing of initiation and termination of glaciations.

 

While there is a Milankovitch cycle in the range of 100,000 years, related to Earth's orbital eccentricity, its contribution to variation in insolation is much smaller than those of precession and obliquity. The 100,000-year-problem refers to the lack of an obvious explanation for the periodicity of ice ages at roughly 100,000 years for the past million years, but not before, when the dominant periodicity corresponded to 41,000 years. The unexplained transition between the two periodicity regimes is known as the mid-Pleistocene transition, dated to some 800,000 years ago.

 

Hypotheses to explain the problem

 

Climatic resonance

The mechanism may be internal to the Earth system. The Earth's climate system may have a natural resonance frequency of 100ka; that is to say, feedback processes within the climate automatically produce a 100ka effect, much as a bell naturally rings at a certain pitch.[6][7] Opponents to this claim point out that the resonance would have to have developed 1 million years ago, as a 100ka periodicity was weak to non-existent for the preceding 2 million years. This is feasible — continental drift and sea floor spreading rate change have been postulated as possible causes of such a change.[8] Free oscillations of components of the Earth system have been considered as a cause,[9] but too few Earth systems have a thermal inertia on a thousand-year timescale for any long-term changes to accumulate. The 100,000 year problem has been scrutinized by José A. Rial, Jeseung Oh and Elizabeth Reischmann[10] who find that master-slave synchronization between the climate systems natural frequencies and the eccentricity forcing started the 100ky ice ages of the late Pleistocene and explain their large amplitude.

 

 

I just happen to be a fan of Milankovitch cycles and in particular the model that includes the natural resonance mechanism. This may be speculative and turn out to be completely wrong, but it makes sense to me and, if nothing else, thinking about it does provide an interesting intellectual pastime.

 

I don’t find Ruddiman’s theory compelling because it only goes back as far as the Late Holocene and certainly has nothing to do with cycles of glaciation that have been going on for millions of years. That does not mean I don’t believe in AGW, just that I think there are much larger factors in play here. AGW is the tail shaking the dog, and the dog has been shaking for a million years before any humans came along.

 

The planet IS going to get warmer in the future, we can be sure of that. And, I might add that I don’t think that is necessarily something we should be worried about. We can adapt to the increased solar radiation and even Jujutsu the sun by using those rays to power our (solid-state) air conditioners.

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The planet IS going to get warmer in the future, we can be sure of that. And, I might add that I don’t think that is necessarily something we should be worried about. We can adapt to the increased solar radiation and even Jujutsu the sun by using those rays to power our (solid-state) air conditioners.

Increased solar radiation?  From what?  Do you mean the way the sun has always been heating up by about 0.01% per each million years?

Sure, "we can adapt," (with nifty air conditioners?) but what about the biodiversity, the resource services, and the food chains upon which we depend?

 

 

Undeniably there are problems with the Milankovitch theory, but there are also proposed solutions.

I will just go the easy route and quote Wiki:

 

I just happen to be a fan of Milankovitch cycles and in particular the model that includes the natural resonance mechanism. This may be speculative and turn out to be completely wrong, but it makes sense to me and, if nothing else, thinking about it does provide an interesting intellectual pastime.

 

I don’t find Ruddiman’s theory compelling because it only goes back as far as the Late Holocene and certainly has nothing to do with cycles of glaciation that have been going on for millions of years. That does not mean I don’t believe in AGW, just that I think there are much larger factors in play here. AGW is the tail shaking the dog, and the dog has been shaking for a million years before any humans came along.

 

I think many of us are fanatical about the reality of the effect of Milankovitch cycles on the climate. 

 

And sure, the Milankovitch cycle explains a lot, and there is evidence going back for hundreds of millions of years showing the signals of its regular effects.  But with today’s configuration of continents, the only way for the Milankovitch cycle to affect the pattern of ice growth/retreat, is with CO2 levels remaining below ~500 ppm.

~Above that level, ~or more likely above 350 ppm, the ice will not be sustainable over any long term, regardless of any Milankovitch configuration.  ISTM it’s only at low CO2 levels, when enough ice can form, that the Milankovitch cycle will affect the ice growth and retreat pattern.

 

Or words to that effect; but the point is, Albedo is a much stronger forcer than Milankovitch.  Albedo trumps Milankovitch, except for that one configuration with a very white polar region.  

With too much or too little ice, the Milankovitch configuration couldn’t have much effect on the pattern of ice growth or retreat. 

 

So sure, the “natural resonance mechanism” would change as the planet cools and average albedo changes over thousands to millions of years.

The “very recent” evolution of the “temperate soils,” those carbon-rich agricultural Mollisols and Chernozems—sometimes called “interglacial soil” (hint, hint)—is another (relatively "new") part of that natural resonance mechanism.

 

Albedo has a huge effect on the yearly average amount of heat coming into the earth system. 

However, Milankovitch cycles don’t even change the yearly average amount of heat coming into the earth system, but it simply changes the distribution of that heat by latitude or season.  So it shouldn’t be surprising that many factors could easily change or easily overwhelm the small, delicately balanced, effect that Milankovitch has on any existing ice balance.

===

 

That is the point Ruddiman makes, about how the natural climate pattern has been decoupled (to some extent) from the Milankovitch pattern, by artificially raising the levels of greenhouse gases.  For some few thousands of years now, we’ve unintentionally been offsetting the expected natural (Milankovitch) cooling trend, thereby keeping the climate fairly level.  Very recently, we’ve been unintentionally overcompensating for the calculated Milankovitch cooling trend.  But now that we know about it, our overcompensation will become intentional, unless we intentionally work to maintain a relatively stable greenhouse level.

===

 

Just look how short the interglacial peaks are, and how much variability there is within each glacial cycle ...at the scale of 400kyr.

 

Then look at how “level” our Holocene climate has been, compared with any previous period of similar length. 

And when you zoom in on the most recent little “red shelf” on the right-hand side above, it looks exceptionally level, at a magnified scale (below) over 50kyr.

 

...and even more stable and level, at the scale of 18kyr.

greenland.18kyr.gif

 

...of course these ice core records don't show the 20th century warming, but....

 

Doesn't the Holocene climate seem unusually stable, as if perhaps another fairly "new" factor had been introduced?

~

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I think many of us are fanatical about the reality of the effect of Milankovitch cycles on the climate. .....

~

 

 

Yeah, we need to keep an eye on those Milankovitch extremists! :rofl: 

 

First off, I don’t think we actually are in disagreement here, it is more likely we are focusing on different questions, or at least different aspects of the same question.

 

The OP was:Increase In Earth's Temperature, What Is The Reason?”

 

My answer is this planet has been going through cycles of glaciation and inter-glacial periods that can be explained by the Milankovitch cycles, and these have been continuing for millions of years and have nothing at all to do with human activity or AGW.

 

Now, if the OP asked “Why is the Earth’s temperature increasing at a faster rate now, than it has in the past?”

 

That is an entirely different question, and the answer to that has to do with AGW, and in particular the amount of CO2 that human activity has added to the atmosphere in relatively recent years.

 

With that clarification in mind, I will attempt to address other points you raise and I apologize for any I miss:

 

“And sure, the Milankovitch cycle explains a lot, and there is evidence going back for hundreds of millions of years showing the signals of its regular effects.  But with today’s configuration of continents, the only way for the Milankovitch cycle to affect the pattern of ice growth/retreat, is with CO2 levels remaining below ~500 ppm.”

~Above that level, ~or more likely above 350 ppm, the ice will not be sustainable over any long term, regardless of any Milankovitch configuration.  ISTM it’s only at low CO2 levels, when enough ice can form, that the Milankovitch cycle will affect the ice growth and retreat pattern"

 

 I don’t quite understand what role the configuration of continents plays in all of this. Who is concerned about ice forming at High levels of CO2? The glaciation occurs when CO2 levels are Low and the inter-glacial (where we are heading now) is when the CO2 levels are high.

 

“Albedo is a much stronger forcer than Milankovitch.  Albedo trumps Milankovitch, except for that one configuration with a very white polar region.” 

 

I don’t see how you can separate albedo from Milankovitch, as you are doing, and say that one trumps the other. They are both related and part of the bigger picture. If Milankovitch cycles have been *cycling* for millions of years, (and they have) then albedo has been going through cycles also. One follows the other, but which of them is in the lead?

Also, there will always be short-term variations superimposed on the long-term trend. These variations are known as regression toward the mean;  the phenomenon when an extreme value of a variable is observed, the next measurement will generally be less extreme.

 

“So sure, the “natural resonance mechanism” would change as the planet cools and average albedo changes over thousands to millions of years.”

Agreed

 

“The “very recent” evolution of the “temperate soils,” those carbon-rich agricultural Mollisols and Chernozems—sometimes called “interglacial soil” (hint, hint)—is another (relatively "new") part of that natural resonance mechanism.”

 

OK.

 

“Albedo has a huge effect on the yearly average amount of heat coming into the earth system.”

 

I think this statement needs some clarification/explaining, so I will do my best:

If, by *earth system* you mean the planet and its atmosphere, then, albedo does not have any effect on the amount of heat coming into that system. The amount of solar energy at visible light wavelengths coming into the system yearly stays fairly constant. Most of that energy gets radiated back into the atmosphere as Infra-red radiation. O2 or N2 molecules in the atmosphere do not absorb IR so most of it just passes through back into space. CO2 does have vibrational modes that are IR active. CO2 (and other greenhouse gasses) will absorb an IR photon and become vibrationally *excited*. Secondary intermolecular collisions occur so there is an overall thermal effect which heats the atmosphere. Now, energy must be conserved, so these excited molecules emit their excess energy in the form of more IR radiation (at lower frequencies). Some of that goes into space and some goes back to the earth’s surface. End result, the surface is warmer than it would be without the CO2 in the atmosphere.

Point of all this is, albedo (in the form of GHG) doesn’t increase the average amount of heat coming in; it lets less escape, so the equilibrium temperature will be higher. Maybe that is a nit-pick, but I think it is an important one.

 

"However, Milankovitch cycles don’t even change the yearly average amount of heat coming into the earth system, but it simply changes the distribution of that heat by latitude or season.  So it shouldn’t be surprising that many factors could easily change or easily overwhelm the small, delicately balanced, effect that Milankovitch has on any existing ice balance”.

 

Again, you are focusing on short-term effects, while I have been focusing on the long-term cycles of glaciation that have nothing to do with human activities. The evidence is these cycles have been happening for millions of years, so they cannot be anthropogenic in nature. As for the short-term trend, yes, it is of great importance to us that are here now, but we should understand that the long-term trend will prevail no matter what we do. That doesn’t mean we do nothing about climate change, we need to cut down on our use of fossil fuels and make more use of other energy, and that includes nuclear power, in my opinion. We also should be at least planning for the eventual relocation of major cities away from the coastlines. It might take 1000 years or more before the maximum temperatures are reached, and the big melt happens, but there is nothing wrong with preparing our descendants for what is coming. Personally, I am trying to purchase some shore front property on the Arctic Ocean so my descendants can enjoy yachting in the temperate Arctic 2000 years from now. :cool: 

 

 

“That is the point Ruddiman makes, about how the natural climate pattern has been decoupled (to some extent) from the Milankovitch pattern, by artificially raising the levels of greenhouse gases.  For some few thousands of years now, we’ve unintentionally been offsetting the expected natural (Milankovitch) cooling trend, thereby keeping the climate fairly level.  Very recently, we’ve been unintentionally overcompensating for the calculated Milankovitch cooling trend.  But now that we know about it, our overcompensation will become intentional, unless we intentionally work to maintain a relatively stable greenhouse level”.

 

OK. I think we are basically in agreement but were on different pages in the same book. Or something like that.

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Although the release of carbon sequestered in fossil fuels by humans is relatively new, the temperature increase has been pretty well sustained for the duration of recorded human history (see the graphs in post #27 and others).  The major cause must be primarily an outside source, and for some reason most studies ignore the impact of the sun.  The sun, which is middle-aged at about 4.5 billion years old, has been getting brighter and larger as it ages.  Earth will eventually become uninhabitable long before the sun consumes it.  You should probably wait a bit before packing.

 

544px-Solar_evolution_%28English%29.svg.

Edited by fahrquad
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The surface temperature of the sun has been relatively consistent, but increased luminosity implies increased infrared light, among other frequencies, so radiant heating has to be a factor. 

 

The luminosity varies quite a bit over Billions of years, but if you zoom in on the time span that covers the Holocene (9,700 BC to present) it will be perfectly flat, so nothing to do with any temperature change we are seeing. What we are seeing is the normal cycle described by the Milankovitch cycles with AGW superposed on it, plus a few other facts we haven’t quite figured out yet

 

But we still have quite a bit of warming up to do if we are to match the temperatures reached during the last inter-glacial 125 kyr ago:

 

With polar temperatures ~3–5 °C warmer than today, the last interglacial stage (~125 kyr ago) serves as a partial analogue for 1–2 °C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6 m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0 m but is unlikely (33% probability) to have exceeded 9.4 m.

 

 

And that was without AGW!

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Yeah, we need to keep an eye on those Milankovitch extremists! :rofl: 

First off, I don’t think we actually are in disagreement here, it is more likely we are focusing on different questions, or at least different aspects of the same question.

 

The OP was:Increase In Earth's Temperature, What Is The Reason?”

 

My answer is this planet has been going through cycles of glaciation and inter-glacial periods that can be explained by the Milankovitch cycles, and these have been continuing for millions of years and have nothing at all to do with human activity or AGW.

 

But if the question is about the “Increase In Earth’s Temperature,” then why suggest the orbital cycle at all?   That cycle has been in a cooling phase for over 10,000 years now.  Milankovitch is a good answer for explaining past glacial/interglacial cycles, but the correlation falls apart as an explanation for the present.

 

 

Now, if the OP asked “Why is the Earth’s temperature increasing at a faster rate now, than it has in the past?”

 

That is an entirely different question, and the answer to that has to do with AGW, and in particular the amount of CO2 that human activity has added to the atmosphere in relatively recent years.

 

Well, you are perfectly correct here!  And it’s a good point, since my answer was mostly about the question of why Earth’s temperature hasn’t been decreasing for millennia …or why the Earth’s temperature has been relatively constant for millennia. 

Just contrast the “long flat line” from our Holocene temperatures with ten thousand years of Eemian (at ~130,000 yr) temperatures!

 

 

With that clarification in mind, I will attempt to address other points you raise and I apologize for any I miss:

 

“And sure, the Milankovitch cycle explains a lot, and there is evidence going back for hundreds of millions of years showing the signals of its regular effects.  But with today’s configuration of continents, the only way for the Milankovitch cycle to affect the pattern of ice growth/retreat, is with CO2 levels remaining below ~500 ppm.”

~Above that level, ~or more likely above 350 ppm, the ice will not be sustainable over any long term, regardless of any Milankovitch configuration.  ISTM it’s only at low CO2 levels, when enough ice can form, that the Milankovitch cycle will affect the ice growth and retreat pattern"

 

 I don’t quite understand what role the configuration of continents plays in all of this.

Because the Milankovitch cycle can’t explain how polar ice initially could come to exist.  Along with the position of the continents, low CO2 levels can allow the ice to exist, while Milankovitch variations can only cause the ice extent to advance or retreat.

 

 

Who is concerned about ice forming at High levels of CO2? The glaciation occurs when CO2 levels are Low and the inter-glacial (where we are heading now) is when the CO2 levels are high.

You seem to be saying Milankovitch, rather than CO2, would determine if glaciation could occur.  But since Milankovitch signals show regularity over hundreds of millions of years, during a mostly ice-free history, that can’t be it.

But also, defining “inter-glacial” as “where we are heading now” is wholly misleading.  We’ve been heading out of the Milankovitch-induced interglacial phase for some millennia already.  Maybe it wasn’t clear on that first graph posted above, but that Milankovitch (interglacial) peak was 11,000 years before time zero (the present).  We should have long been cooling, according to Milankovitch, and yet we are now heading for another cycle of increasing Milankovitch warmth forcing.  Do you see how this is shown?

 

insolation-at-65-north.jpg

 

I suppose I define high CO2 and low CO2 differently.  High levels geologically, would mean over ~350 ppm, where ice seems to be unsustainable.  Low levels would mean ice can form easily, and remain or grow …or depending on the cyclical increase of insolation at 65 °N latitude (plus feedbacks), the ice extent could also temporarily retreat. 

 

 

 

“Albedo is a much stronger forcer than Milankovitch.  Albedo trumps Milankovitch, except for that one configuration with a very white polar region.”

 

I don’t see how you can separate albedo from Milankovitch, as you are doing, and say that one trumps the other. They are both related and part of the bigger picture. If Milankovitch cycles have been *cycling* for millions of years, (and they have) then albedo has been going through cycles also. One follows the other, but which of them is in the lead?

With no ice, (through most of geologic time) Milankovitch couldn't change albedo.  But low CO2 levels would allow the ice to form, and then Milankovitch variations will cause the ice extent to advance or retreat.  As soon as the 65 °N latitude insolation declines back toward average or below, the ice stops retreating, and ice growth returns …normally.  At least that is the way it seems to have worked for several million years, until this last Milankovitch peak.

 

 

 

“Albedo has a huge effect on the yearly average amount of heat coming into the earth system.”

 

I think this statement needs some clarification/explaining, so I will do my best:

 

If, by *earth system* you mean the planet and its atmosphere, then, albedo does not have any effect on the amount of heat coming into that system. The amount of solar energy at visible light wavelengths coming into the system yearly stays fairly constant. Most of that energy gets radiated back into the atmosphere as Infra-red radiation. O2 or N2 molecules in the atmosphere do not absorb IR so most of it just passes through back into space. CO2 does have vibrational modes that are IR active. CO2 (and other greenhouse gasses) will absorb an IR photon and become vibrationally *excited*. Secondary intermolecular collisions occur so there is an overall thermal effect which heats the atmosphere. Now, energy must be conserved, so these excited molecules emit their excess energy in the form of more IR radiation (at lower frequencies). Some of that goes into space and some goes back to the earth’s surface. End result, the surface is warmer than it would be without the CO2 in the atmosphere.

 

Point of all this is, albedo (in the form of GHG) doesn’t increase the average amount of heat coming in; it lets less escape, so the equilibrium temperature will be higher. Maybe that is a nit-pick, but I think it is an important one.

I’m sorry I wasn’t clear on this point.  I should have said: "Albedo has a huge effect on the yearly average amount of energy retained by the earth system."  

I’m not sure what you mean though, by talking about “albedo (in the form of GHG),” when describing the basic greenhouse mechanism. 

 

 

"However, Milankovitch cycles don’t even change the yearly average amount of heat coming into the earth system, but it simply changes the distribution of that heat by latitude or season.  So it shouldn’t be surprising that many factors could easily change or easily overwhelm the small, delicately balanced, effect that Milankovitch has on any existing ice balance”.

 

Again, you are focusing on short-term effects, while I have been focusing on the long-term cycles of glaciation that have nothing to do with human activities. The evidence is these cycles have been happening for millions of years, so they cannot be anthropogenic in nature. As for the short-term trend, yes, it is of great importance to us that are here now, but we should understand that the long-term trend will prevail no matter what we do. That doesn’t mean we do nothing about climate change, we need to cut down on our use of fossil fuels and make more use of other energy, and that includes nuclear power, in my opinion. We also should be at least planning for the eventual relocation of major cities away from the coastlines. It might take 1000 years or more before the maximum temperatures are reached, and the big melt happens, but there is nothing wrong with preparing our descendants for what is coming. Personally, I am trying to purchase some shore front property on the Arctic Ocean so my descendants can enjoy yachting in the temperate Arctic 2000 years from now.   :)

Maybe you think I’m talking about “short-term effects” (of the Milankovitch cycle) because I mentioned the “yearly average,” but no.  Let me try again.  Throughout the entire Milankovitch cycle, over thousands and tens of thousands and hundreds of thousands and across millions of years, wherever Earth is within that cycle (of the multiple cycles of tilt and asymmetries), there is no change to the total amount of incoming solar insolation ...averaged over the whole planet for a whole year.

 

Obviously there are changes to the distribution of that total amount of insolation, but the Watts per square meter of insolation stay the same for the global system, regardless of whatever phase of any Milankovitch cycle we might be in.  Do you see how that works?

 

Albedo has huge effects on the amount of energy absorbed or reflected by the planet, whereas Milankovitch has zero effect of the amount of energy that the planet receives.  If Milankovitch does have any effect on temperature, it is because the cycle does change the distribution of insolation relative to some local albedo feature   …such as a very white polar cap, if one happens to exist. 

When a planet has uniform albedo, then Milankovitch-type of changes should have no effect on temperature.  With a difference in albedo though, Milankovitch changes can alter the amount of (the constant incoming) energy that becomes absorbed/reflected by the albedo, and that can then affect temperature.  Does that make sense?  :huh: 

 

 

“That is the point Ruddiman makes, about how the natural climate pattern has been decoupled (to some extent) from the Milankovitch pattern, by artificially raising the levels of greenhouse gases.  For some few thousands of years now, we’ve unintentionally been offsetting the expected natural (Milankovitch) cooling trend, thereby keeping the climate fairly level.  Very recently, we’ve been unintentionally overcompensating for the calculated Milankovitch cooling trend.  But now that we know about it, our overcompensation will become intentional, unless we intentionally work to maintain a relatively stable greenhouse level”.

 

OK. I think we are basically in agreement but were on different pages in the same book. Or something like that.

...or maybe a revised edition of the same book?  ;) 

 

~

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But also, defining “inter-glacial” as “where we are heading now” is wholly misleading.  We’ve been heading out of the Milankovitch-induced interglacial phase for some millennia already.  Maybe it wasn’t clear on that first graph posted above, but that Milankovitch (interglacial) peak was 11,000 years before time zero (the present).  We should have long been cooling, according to Milankovitch, and yet we are now heading for another cycle of increasing Milankovitch warmth forcing.  Do you see how this is shown?

 

insolation-at-65-north.jpg

 

 

 

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This is where I disagree. In talking about such a large and complex system as the Milankovitch cycle , it is just not possible to accurately pin down where we are at present.

 

The Milankovitch cycle acts as an initiator of the process, both warming and cooling, and does not exert a continuous influence over it. There can be large lag times between stimulus and response in such a large elastic system. Some inter-glacial periods have lasted for tens of thousands of years while others have been much shorter. I am highly skeptical of anyone who points to a position on a graph and says “you are here” or “you should be there.”

 

Especially now, when there is forcing due to human influence, it is very hard to pinpoint where we would be if there were no anthropogenic involvement; we could be slightly below, at or even slightly above our inter-glacial "normal" or possibly slightly cooling.

 

Based on the last inter-glacial, (I linked to a paper in my last post) that was much warmer than today and with no anthropogenic inputs, I believe we are still warming according to the natural cycle, with the human influence superposed on top of that.

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