How the Northern Hemisphere Drives the Modern Climate


Over the past several million years the geography of the Northern Hemisphere (NH) developed into the driving force in the Earth’s climate.  This can be seen in the annual temperature variation (Jones 99).

The Inconvenient Skeptic

Annual Temperature behavior of the Earth

Notice that the global temperature tracks with the seasons of the NH.  The reason for this is simple.  The NH has twice as much land as the Southern Hemisphere (SH).  Oceans do not change temperatures in the same manner that land does.  So every year when there is almost a 4 °C swing in the temperature of the Earth, it follows the seasons of the NH.  This is especially interesting because the Earth gets the most energy from the sun in January right now.  That is because of the orbit of the Earth.  The perihelion is when the Earth is closest to the sun and that currently takes place in January.

The small annual variation in the energy from the sun makes little difference right now to the Earth’s climate.  That is because the SH is tilting to the sun at that time of year instead of the NH.  This is a good example of local energy changes mattering more than the total global energy changes.  The NH receives less energy in the winter than it does in the summer.  Again, that is because of the Earth’s tilt.

So even though the Earth is closest to the sun while it is receiving the most energy from the sun, the Earth is the coldest at that time of year because the NH is away from the sun.  Looking at local amounts of energy can be critical to understanding how climate changes over time.  Here is the difference in energy that a mid-latitude location gets on a daily basis for two different times of year.

The Inconvenient Skeptic

NH Summer and Winter Energy Differences

The tilt causes the magnitude and duration of energy to vary in the NH by the time of year.  It is this variation in the daily energy that causes the seasons.  It is very important to understand that even though the Earth is getting more total energy from the sun on Dec 21 than it is on June 21, the Earth is colder on Dec 21 because the NH is tilted away from the sun.  Land warms and cools more than the oceans do.  Because the NH has twice as much land as the SH it sees more warming and cooling based on the amount of energy it gets from the sun.

Why does this matter so much?  In the debate about global warming, people often try to focus on the total energy while completely ignoring the local energy.  When the Earth warmed from the last glacial (ice age) to the current climate, it did so because of a change in the local energy that the NH gets in the summer.  Even though the total energy the Earth received from the sun had very little change, the amount of energy the NH recieved during the summer months changed by a large amount.

Right now the NH has an annual temperature range of 8-21 °C.  The SH has an annual temperature range of 11-17 °C.  In the coldest periods of the last glacial, the average temperature of the Earth was about 5 °C colder than it is today.  That does not mean that every place on Earth was 5 °C colder.  What it means is that the NH was much colder than it is today.  The tropics were still the tropics during the last glacial.  The difference in the global temperature was caused by a large part to a much colder NH.  When the NH is much colder it causes the average temperature of the Earth to drop.

The Inconvenient Skeptic

LGM Temperature Anomaly estimate.

Estimate from: Northern Hemisphere Ice-Sheet Influences on
Global Climate Change

Peter U. Clark, Richard B. Alley, David Pollard

The other factor is the sea levels.  They were more than 100 meters lower than they are today.  That caused other changes to the Earth’s climate.  That water that wasn’t in the ocean was locked up in the ice sheets that covered much of North America and Europe.  The oceans near both poles were colder while the sea levels were lower.  One of the changes caused by the colder oceans was the reduction in atmospheric CO2 as the colder water absorbed more CO2 from the atmosphere.  That is a partially why CO2 levels change with the temperature of the oceans.  Colder water absorbs CO2 from the atmosphere and warmer water CO2 releases into the atmosphere.

Many methods in determining the climate sensitivity depend on using the change in overall energy and the overall change in temperature to determine the climate sensitivity.  Since there is a small overall change in energy to the Earth, but the average temperature of the Earth changes, the estimated climate sensitivity is higher than it actually is.  The strong solar forcing in the NH causes a strong response in the NH that then causes a change to the rest of the Earth’s climate.  In the case of climate sensitivity there is a significant difference between what is happening on a global scale and directly to the Northern Hemisphere.  Just like the annual seasons are caused by local energy levels to each hemisphere, the current glacial cycles are also determined by local energy levels.  This is why the climate sensitivity is overstated when the glacial/interglacial transitions are analyzed.

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Posted in Climate by inconvenientskeptic on October 26th, 2010 at 1:33 am.

8 comments

This post has 8 comments

  1. Glenn Tamblyn Oct 27th 2010

    John

    Several points.

    Your graph of seasonal temp variations for NH/SH & Globe. What is the source for this – surface records in which case it is an amalgum of SST’s and Land station temps, or Satellites, in which case it is all atmospheric. Perhaps better captions are needed for your diagrams identifying sources.

    Again with your second graph, a reader could easily assume that this graph applies to mid-latitudes for BOTH hemispheres when in fact you are showing just the NH data, thus believing that the seasonal variation in GLOBAL incoming energy is this great – the variation between apehelion and perehelion is nowhere this magnitude.

    Then the fundamental problem with the conclusion you are trying to draw from this is that you are focusing on just the change in air temperatures (and perhaps SST’s). You are focusing on Temperature, rather than energy change.

    A far more useful graph would use the thermal mass of the air in each hemisphere and the thermal mass of that part of the oceans in each hemisphere that is involved in seasonal variation – probably the well Mixed Layer down to around 100m. Calculate the energy variation for each of these components over the season and plot NH vs SH for that. I suspect you will see much much less variability North/South. I know this is a harder calc but it would be MUCH MORE Meaningful.

    So your comments at the end

    “The strong solar forcing in the NH causes a strong response in the NH that then causes a change to the rest of the Earth’s climate.”

    I would completely disagree with this. You are not looking at the climate North or South. You are looking at the atmospheric component of the climate, which is very much the tail that tries to wag the dog.

    “Just like the annual seasons are caused by local energy levels to each hemisphere, the current glacial cycles are also determined by local energy levels.” You haven’t looked at local energy levels. You have only looked at local ATMOSPHERIC energy levels. More Tail and Dog.

    Recall the figures I cited for you about the relative energy increases in the different parts of the climate system:

    “Here are some figures from the March 2009 copenhagen Conference Synthesis report on energy accumulated between 1961 & 2003, all in 10^22 Joules

    Oceans 14.2
    Glaciers & Ice Caps 0.22
    Greenland Ice Sheet 0.02
    Antarctic Ice Sheet 0.06
    Continents 0.76
    Atmosphere 0.5
    Arctic Sea Ice 0.15

    The atmosphere is only a small part, around 3%, of the total energy change over that period. All Ice effects are nearly as great, land is more and Oceans are the elephant in the room at nearly 90%.”

    How can an analysis that just focuses on the atmospheric temperature, not even the atmospheric heat content be terribly useful in isolation. Just watching the tail won’t tell you much about the dog!

    So to your claim that the Northern Hemisphere drives the Climate. Not from what you have presented here it doesn’t.

    Time to look at the oceans and heat content!

  2. inconvenientskeptic Oct 27th 2010

    Glenn,

    Sorry, I missed getting that in there. It is actually Phil Jones 1999. It is added now. I also added a NH to the 2nd chart. I agree that clarifies the chart.

    That it is air temperature is irrelevant in this case. The oceans also cool from the Bahama’s to the North Pole. Snow covers significant fractions of the NH land mass over the course of the winter. The Arctic Sea Ice extent grows more than 10 million km2.

    Just the ice formation alone is a massive amount of energy. Without large heat of fusion of sea water keeping temperatures stable, the temperature drop would even be greater.

    A change in temperature indicates a change in energy. That direct conversion involves total mass and heat capacity doesn’t matter. The air, the oceans and the land all lose temperature and by definition, they all lose heat. Lots of it.

    The energies you describe are just the temperature changes applied by the mass and heat capacity. We know the Earth has warmed, that is all that says.

    How much heat does the Earth lose when the NH is in winter? Including the heat of fusion for 10 million km2 of sea ice. The snowfall across the NH. You will find that the energy magnitudes are pretty high when half the planet drops and average of °C.

    If you could show that water column temperature profiles were higher now than they were 6,000 years ago, that would be impressive, but the Earth was much warmer then, meaning it had more energy then.

    The average temperature of the Earth is fluctuates about 4 °C each year. It does so because the NH has the land and the land is what drives temperature changes.

    Would you agree once you verify the global annual cycle the NH is indeed the driving factor to the Earth’s annual temperature variation?

  3. Glenn Tamblyn Oct 28th 2010

    John

    “That it is air temperature is irrelevant in this case. The oceans also cool from the Bahama’s to the North Pole. Snow covers significant fractions of the NH land mass over the course of the winter. The Arctic Sea Ice extent grows more than 10 million km2.”

    And at the same time oceans cool from the equator to Antarctica, sea ice extent contracts in the SH, Snow melts in the SH.

    “A change in temperature indicates a change in energy. That direct conversion involves total mass and heat capacity doesn’t matter. The air, the oceans and the land all lose temperature and by definition, they all lose heat. Lots of it.”

    In the Northern Hemisphere. And at the same time in the Southern Hemisphere the reverse is happening. Lots of it. What is the net result?

    “How much heat does the Earth lose when the NH is in winter? Including the heat of fusion for 10 million km2 of sea ice. The snowfall across the NH.”

    And including the released heat of fusion of sea ice and snow melt in the Southern Hemusphere. And the increased uptake of heat by the southern oceans during their Summer.

    “You will find that the energy magnitudes are pretty high when half the planet drops and average of °C. ” Not nearly as great as you think because the other half of the planet rises.

    “If you could show that water column temperature profiles were higher now than they were 6,000 years ago, that would be impressive, but the Earth was much warmer then, meaning it had more energy then.”

    The point of those figures is that with any Global warming, the bulk of the energy change occurs in the ocean – last 50 years, Interglacial, full Ice Age, whatever.

    “The average temperature of the Earth is fluctuates about 4 °C each year. It does so because the NH has the land and the land is what drives temperature changes.”

    It could be phrased either way – it is the greater amount of land in the north that drives atmospheric temperature changes. Or it is the greater amount of ocean in the South that moderates atmospheric temperature changes.

    “Would you agree once you verify the global annual cycle the NH is indeed the driving factor to the Earth’s annual temperature variation?”.

    No. As I commented above it can be read either way. And that is only the variation of atmospheric temperature, not the whole environments temperature. Far more important is what the annual change in Total Heat Content for the planet is. Not temperature. Temperature is just a consequence of heat. As an engineer the rule is simple. Follow the heat.

    So, I would instead phrase it that the asymmetry of the continents between north and south results in asymmetrical warming/cooling with the NH seeing greater atmospheric warming/cooling and less oceanic warming/cooling while in the SH it is reversed – greater oceanic warming/cooling and less atmospheric warming/cooling.

    John, you are repeatedly using expressions like ‘the Earth’s …” when actually you are referring to one component of the Earth system, not the system as a whole. So claims about the impact of one component can only be used in discussions about that component. To then extrapolate that to the entire system is invalid. If that is not your intent then you need to be much more precise about your use of language or you can convey the wrong impression.

  4. inconvenientskeptic Oct 28th 2010

    Glenn,

    You correct that it could be looked at from either side, the NH drives more extreme changes and the SH moderates those changes. That is fine either way.

    The actual point is that the decreasing solar energy in the NH results in a decrease in global temperature on an annual basis. Increasing solar energy in the NH results in an increase in global temperature on an annual basis.

    In this way the local, but annual changes in the solar energy drive the global temperatures.

  5. Glenn Tamblyn Oct 30th 2010

    John

    “The actual point is that the decreasing solar energy in the NH results in a decrease in global temperature on an annual basis. Increasing solar energy in the NH results in an increase in global temperature on an annual basis.

    In this way the local, but annual changes in the solar energy drive the global temperatures.”

    Incorrect John

    It is not local changes in Solar energy over the year that drives anything. The Northern and Southern Hemisphere’s have similar variations, after allowing for some variation between Perehelion and Aphelion.

    What differs is the Northen vs Southern Hemisphere responses to the solar variation, due to different proprtions of land vs sea. In the North air temps vary more because there is more land to heat the air. In the south ocean temp’s will vary more because there is more ocean. And ‘globat temperatures’ are the temp of the atmosphere AND the oceans.

    You are still continuing with this focus on just atmospheric temp’s – tail wagging dog.

  6. inconvenientskeptic Oct 30th 2010

    Glenn,

    “The Northern and Southern Hemisphere’s have similar variations, after allowing for some variation between Perehelion and Aphelion.”

    That is incorrect as I stated in the article. Perihelion is the closest approach and that is in January when the Earth is coldest. If perihelion was driving the seasonal difference, then January would be the warmest, not the reverse.

    You have the approaches backwards. June/July should be the coldest now as the Earth is farthest at that point and hence receives the least energy.

    Check that again, the link I have for perihelion gives the dates for closest approach, All are January for the next thousand years.

    The Earth is 4 °C colder when it is getting the most energy on an annual basis. That is a fact. The reason is exactly for the reasons I have stated.

    Please re-check that for yourself. 4 °C on an annual basis is significant and unrelated to Earth’s overall position to the Sun. Only the relative position of the NH matters in the current geographical configuration of the Earth.

    This also indicates that my focus on the NH is justifiable, or at least potentially valid and worth further investigation.

  7. Glenn Tamblyn Oct 31st 2010

    Again John

    The atmosphere isn’t the climate. It is one small part of it.

    Go back to your Engineering days John. Hopefully your lecturers drumed into you just as forcefully as mine did that any meaningfull analysis in thermodynamics depends critically on drawing the right system boundary. Get the system boundary wrong and your analysis will be wrong. Focusing on just the atmosphere has the system boundary wrong.

    There will be variations over the oscillation between perehelion & aphelion, and these will vary in magnitude over the Milankovitch cycles. But if your SB is wrong you will miscalculate the magnitude of these variations because you will be ignoring the intra-system energy flows. And since the ocean is thermally vastly more massive, any analysis that ignores this will produce wildly incorrect results.

    I repeat. The atmosphere isn’t the climate.Its just the small part of it we happen to live in. And given the vastly different specific heats of the air vs the ocean, comparisons based on temps are rather meaningless. Compare the energy content.

  8. Thanks for the post

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