Climate Sensitivity of the Northern Hemisphere


While most people agree that the variations in the orbital parameters are the triggers for the beginning and end of the glacial/interglacial cycles, it is the magnitude of the change caused by the energy changes (forcing) that is disagreed upon.  Many attempts are made to point out how small the change is in the total orbital forcing.  The problem is that they are looking at the Earth as a whole and not the local effect on the Northern Hemisphere.  As I pointed out in Tuesday’s post, local changes in the Northern Hemisphere’s energy can have a big influence on the Earth’s climate.

Over the past 450,000 years there have been several major glacial/interglacial (ice age/current climate) cycles. The current interglacial has been “warm” for about 11,000 years now.  This period is very commonly referred to as the Holocene interglacial.  The current interglacial was “triggered” by a change in the orbital parameters of the Earth’s orbit that caused the NH to have a period where the amount of energy it received during the summer increased 11%, or about 50 W/m2.  The temperature of the NH changed about 12-14 °C with that change in energy.  As explained in depth in a previous article, the reason NH is more significant is because it has twice as much land as the SH does.  This causes it to warm and cool more than the SH.

The Inconvenient Skeptic

Earth during the last glacial

What has typically happened when determining the climate sensitivity for the transition from glacial to interglacial is a calculation where the total change in energy to the Earth is used.  This is then used with the total change in temperature of the Earth.  The fundamental problem with this approach is that there is little change in the total energy because the increase in NH energy is counter-balanced by a loss in SH energy levels.  A typical sample of this type of work is here.  The result looks like this.

λ = (5°C /  7.1W/m2 ) = 0.7 °C/(W/m2)

Since the decrease in SH energy levels have almost no influence on what is happening in the NH, the overall climate sensitivity is overstated.  The change in forcing that matters is the increasing energy in the NH.  If the climate sensitivity for the NH is analyzed by itself, the result is very different.  Here are the climate sensitivity calculations for the NH for the transition from the Last Glacial Maximum (LGM) to the Holocene Interglacial.  I used the 12-14 °C  temperatures described in the last NH article.

λ(12°C) = (12°C /  50 W/m2 ) = 0.24 °C/(W/m2)

λ(14°C) = (14°C /  50 W/m2 ) = 0.28 °C/(W/m2)

While the temperature change is larger for the NH alone, so is the change in solar energy (forcing).  Although change in forcing is slow, it is relentless.  Every summer, over the course of 10,000 years, gets slightly more energy than the summer before.  This results in more and more melting of the ice sheets.  Summers 10,000 years ago in the NH received 10% more solar energy than the they do now.

The next analysis is from the initiation of the Eemian Interglacial that happened 135,000 years ago.  This transition had a stronger solar forcing than the Holocene did.  The total energy change from 135,000 – 126,000 years ago was 65 W/m2.   The Eemian interglacial also had a total peak energy that was about 15 W/m2 higher than the Holocene.  Determining the temperature change is done by comparing the LR04 Benthic and the EPICA data.  This shows that the starting point for the two periods were likely comparable.  The EPICA data also indicates that the peak Eemian temperature 126,000 years ago was 4 °C warmer than the Holocene.  So I will use a range of 16-18 °C for the Eemian sensitivity calculation.

λ(16°C) = (16°C / 65  W/m2 ) = 0.25 °C/(W/m2)

λ(18°C) = (18°C /  65 W/m2 ) = 0.28 °C/(W/m2)

This compares favorably to the Holocene result for sensitivity.

In both cases the increase in NH energy coincided with a decrease in SH solar forcing.  When the NH increase is averaged with the SH decrease, the average net change is little.  In the case of the glacial cycles, much like the seasons, it simply doesn’t matter that there is little change in the total energy.  It is the local energy in the NH that drives the change locally and then the local changes cause the global change.

Both results also indicate that the IPCC estimates for sensitivity are significantly overstated.  Here is the conversion table for climate sensitivity in the range of 0.24 – 0.28 °C/(W/m2) when converted to the commonly used temperature change per doubling of CO2.

The Inconvenient Skeptic

Climate Sensitivity Conversion

Assuming the CO2 forcing model that is commonly used by the warmists is accurate, then the warming caused by a doubling of CO2 is in the range of 0.89-1.04 °C.  It would also indicate that the warming that could be attributed to the increase in CO2 for the past 100 years is about 0.4 °C.  The next additional 0.4 °C increase would be reached when the CO2 levels reached 543 ppm.

I am not claiming that their forcing model is correct, I will get to that in due time.  I will currently say that their climate sensitivity is overstated and the projected temperature increases are equally overstated.

Note:  I will continue to use the °C/(W/m2) units because not all readers are familiar with the Kelvin scale.  I try to make my articles readable to as many people as possible.

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Posted in Climate and Science Articles - Global Warming by inconvenientskeptic on October 28th, 2010 at 3:09 am.

3 comments

This post has 3 comments

  1. Glenn Tamblyn Oct 29th 2010

    John

    There is a fundamental problem with what you are doing here – apart from the objections I have raised about your earlier points.

    You are taking your analysis of variations over a 1 year cycle which you incorrectly refer to as the NH’s influence on Climate. Firstly, wrong title. 1 year isn’t Climate, its Weather.

    Then you are trying to use this to establish some NH only CS. This is meaningless. While the annual cycle you observe is real, it exists because the mixing processes in the atmosphere and more importantly in the oceans, do not transport that much energy between the hemispheres over the time scale of a single year.

    Inter-Hemispheric mixing time for the lower atmosphere is more like 1-2 years. In the stratosphere it is more like 5 years. Ocean currents cycle water all around the world and from the surface to the deeps. It is estimated that a ‘parcel’ of water may take around a 1000 years to travel the worlds currents and return to where it came from.

    So on a less than 1 year timescale mixing doesn’t balance heat between North & Souith that much. But on time scales of centuries to millenia, the time scales applicable for looking at Ice Core data, the environment is VERY well mixed North to South and Top to Bottom. Therefore, any changes in energy uptake on these timescales, whether North or South, Air or Oceans, will be well mixed and distributed around the globe

    So, just using the change in energy for the NH alone during a Milankovitch cycle is totally invalid and meaningless. As is the idea of a NH only CS. The world is too well mixed for that.

    So a statement such as
    “Since the decrease in SH energy levels have almost no influence on what is happening in the NH,”

    Is Totally Completely And Utterly Wrong. Thermodynamic, Fluid Mechanical, Meteorological and Oceanographic Nonsense!

    Energy levels between the hemispheres are extremely well mixed on long time scales. Long starting at anything above a few years for the atmosphere and decades or longer for the oceans.

    This is the fallacy you are making of projecting a less-than-1-year timescale behaviour onto a millenium timescale behaviour. That is a nonsense that completely ignores meteorology, oceanography and basic thermodynamics. NH and SH are Absolutely NOT disconnected on these timescales.

    Therefore, your use of 65 W/M^2 as the forcing in your calculation is totally invalid. Yes the NH receives MORE energy at one end of the Milankovitch cycle (MC). But the SH receives almost the same amount LESS. And atmospheric and ocean circulation mixes these two together very well so the NET Milankovitch forcing is actually the difference between the two.

    The common figure given for the average forcing over a MC is 3.4 W/M^2, not 65. This is the average since each MC is somewhat different as they are actually a conjunction of several different cycles with differing periods.

    So, consider an ‘average’ glacial cycle.

    Milankovitch forcing = 3.4
    Typical CO2 variation is 200ppm to 300ppm.
    So 5.35 * ln(300/200) is 2.17

    Total forcing from these factors is 5.57 W/M^2

    So the CO2 component of the total is just under 40%, the accepted figure.

    And this is the equivalent of around 1.4 doublings of CO2

    Typical temperature range over a glacial cycle is 10 DegC

    So 10 DegC / 1.4 = approx’ 7.

    That is the CS from the Ice Core record.

    I believe this over-states the CS somewhat since we don’t see what impact Methane changes may have and these need to be considered a forcing as well. And comparing a CS over a glacial cycle when Albedo change is significant due to ice sheet changes will overstate the CS in a warmer world that is getting warmer – the ice albedo feedback today under a warming pressure will not be as great.

    So, overall a long term CS of 3 – 5 is not at all implausible.

    The fundamental fallacy in your argument is that you are ignoring North/South mixing and are ignoring energy changes in the SH. This is totally invalid!

    John
    You might want to move this to another thread.

    Consider also what the forcing of CO2 & Milankovitch is over a glacial cycle. The following is a simple simulation of a glacial cycle, starting at the top of an interglacial. It shows the year and the CO2 Alone Forcing and the Combined CO2 & Milankovitch Forcing relative to the top of the interglacial.

    In my simple spreadsheet, Milankovitch varies sinusoidally from 0 to -3.4 and CO2 declines at -2 ppm per millenium from 300 ppm towards 200 ppm. Then to simulate the human influence during the Holocene it then grows back up from the 22000 year mark at 2 ppm per millenium. Then at the 32000 year mark it jumps to 560 ppm to match what is occuring very quickly in the modern era.

    Notice how the CO2 contribution to Forcing starts to reverse from 22000, but the Total Forcing doesn’t reverse, it keeps going down because the Milankovitch component outweighs it.

    Then in the modern era at 32000 in my simulation, CO2 completely takes over resulting in .9 W/M^2 higher than at the Top of the Interglacial

    So using the very figures used for the expected major impact of CO2 in the modern era, the impact of CO2 is outweighed by Milankovitch during the decline from an Interglacial when they are in opposition as they were during the Holocene. When they are in conjunction as after previous interglacials, their impact compounds.

    Thus the ice core record does not support the idea that CO2’s impact will be negligible today. Co2 has a smaller impact during a glacial cycle because it’s magnitude of impact is less than we are expecting today.

    Years from top of CO2 Forcing W/M^2, Combined Forcing,
    InterGlacial WITH Human WITH Human
    Influence Influence

    0 InterGlacial Peak 0.000 0.000
    2000 -0.072 -0.085
    4000 -0.145 -0.198
    6000 -0.218 -0.338
    8000 -0.293 -0.504
    10000 -0.369 -0.694
    12000 -0.446 -0.907
    14000 -0.524 -1.141
    16000 -0.603 -1.393
    18000 -0.684 -1.660
    20000 -0.766 -1.940
    22000 Human Infl’ -0.684 -2.065
    24000 -0.603 -2.197
    26000 -0.524 -2.331
    28000 -0.446 -2.465
    30000 -0.369 -2.594
    32000 Modern Era 3.339 0.915

  2. inconvenientskeptic Oct 29th 2010

    Glenn,

    I am aware what the “normal” Milankovitch cycle forcing used is. I strongly disagree with it.

    There is 50 W/m2 difference in the summer energy that the NH received over the course of 10,000 years. So flawless is the 65N correlation to the global temperature over the past 150,000 years that it is folly to disregard it. It also is the ONLY forcing factor that leads the temperature.

    Perhaps I presented my information out of order, but I will convince you yet. Early next week I will get some correlation stuff together. 🙂

    Thanks,
    John

  3. Malaga View Oct 31st 2010

    Wonderful posting… thank you.

    Although change in forcing is slow, it is relentless

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