Surface atmospheric temperature varies strongly month to month and year to year. The broad brush view is obtained by looking at variations across the decades. SAT by decade

In the broad we can say that in terms of the decadal variations:

  • Temperature in high latitudes is much more variable than in low latitudes.
  • Temperature is much more variable between 30°north latitude and the Arctic than elsewhere.
  • Cooling manifested in the early decades other than in near equatorial latitudes where the extent of temperature change is least.
  • It is clear that temperature change is a two way process.
  • Cooling occurred in the decade after 1986 in the tropics as greenhouse gases accumulated. We have no explanation for this cooling, and that which affected the highest latitudes and the latitude band 30-60° north from 1956 through to 1976 and are unable therefore to be certain that it will not recur.
  • Both the Arctic and the Antarctic began a warming phase starting with the decade 1977-86. The warming in the Antarctic is faster in the early phase but slower in the latter. The Arctic warmed particularly strongly after the turn of the century as the rate of warming in the Antarctic fell away. Greenhouse gases other than ozone are well mixed and vary very little according to latitude. Something other than greenhouse gases must be responsible for the variation in the rate of temperature change according to latitude.
  • In general the temperature of the mid latitudes of the northern hemisphere cooled and warmed with the Arctic but to a lesser extent.
  • The evolution of temperature in the tropics and the mid latitudes of the southern hemisphere is similar. These latitudes cooled slightly as the warming in high latitudes accelerated after 1977-86.


Here we look simply at the difference between the first and the last decade in each month of the year.

change in t by lat

  • The Antarctic warmed in winter and cooled in summer showing more change than the Arctic.
  • The Arctic warmed slightly in summer but a great deal in winter.
  • The mid latitudes of the northern hemisphere at 30-60° north warmed in autumn and spring. This lengthened the growing season in a part of the globe that includes the heartlands of Western Civilization, Western Europe and North America where winters are cold but can sometimes be severely cold. Industrialization and the ready availability of cheap energy have made it possible for these parts of the planet that experience very cold winters and a short growing season to support a greater population. Warming in autumn and spring has assisted this process.
  • We see that warming is in no sense ‘global’. Neither is it consistent  between one month and another.
  • In those places that suffer from cold, warming is temporarily constrained to the cooler winter months. Where winters are unfavourably cold, in fact most of the planet, this is beneficial.
  • Plainly the major dynamic here has nothing at all to do with the concentration of a greenhouse gas that is well mixed. If it were, the warming would vary little between the seasons and there is no reason to expect that it should vary with latitude.
  • If there is a background level of warming due to increasing greenhouse gases that provides a plateau upon which ‘other forces’ superimpose change then we would see that background warming manifest at that time and in that place where the ‘other forces’ are least active. Unless we can decide what those other forces are and be truly cognizant of the mechanism that is behind them we are unable to estimate the change that they are responsible for and can have no idea whether man is having an influence on he climate or not. If we go ahead and suggest/maintain that man is responsible for the warming of the globe as a whole we make an error in logic. We can not be sure of anything. To suggest that man is likely to be responsible and to assert that we can do this with a high level of confidence  is clearly overstepping the mark.

In this circumstance how are we to proceed? Plainly the bulk of the warming that has a seasonal component is not connected with greenhouse gases. We must ask what causes this warming. In particular what is it that causes warming in winter in high latitudes?

In the next chapter we look at the extent of variability in temperature according to the month of the year. We find that there is a consistent pulse attached to warming that indicates its source. At first glance the process of change is apparently  hemispheric in its incidence. However, when we look closer we see a unifying signal emanating from the Antarctic stratosphere that governs all. The degree of warming is very different according to latitude even though it bears a consistent time signature. There is a pacemaker that orders its heartbeat. The closer one approaches the poles the more impressive is the beat of that pulse. That pulse is strictly seasonal. The mechanism is fascinating. It represents a new frontier for climate science. Get out your stethoscope, gather round, here is a curiosity, here is a case that is entirely unfamiliar.




  1. Erl, make sure you don’t get too stridant. There is a reason why you might expect more warming in winter and also more warming where the winters are coldest. This relates to the SB blackbody law of radiation. As you are no doubt aware the energy that it takes to warm a cold body/object by 1 degree is less than the energy needed if the same body is at a warmer starting temperature. Therefore, for a constant amount of forcing, you can expect to warm a cool place more than a hot place. But then I don’t see this effect being able to explain the magnitude of the latitudinal differences you have plotted above.

    By the way the same disproportionate cooling/warming effect also occurs between high and low latitudes on glacial/interglacial timescales.


  2. Rob R. Thanks for the reality check. If the warming was greatest in the coldest months then some radiation forcing factor could be influential. And, in the Arctic the warming is indeed greatest in the coolest months. But in the Antarctic the situation is more complex. In the stratosphere it has been in Spring, peaking in October as temperatures are rising strongly towards the summer maximum. At the surface its a little earlier but still skewed.

    And then there is the anomalous cooling in the summer in the Antarctic to consider. That seems to relate to the southwards migration of the heavy cloud associated with frontal activity. Southwards migration relates to the oft mentioned ‘expansion of the Hadley Cell’ which in my terms is due to the secular increase in atmospheric pressure in the mid altitudes over the last 68 years, mainly in winter, and due to a shift in atmospheric mass from all latitudes south of 50° south. Hence the long term decline in rainfall in the west cost of Western Australia where we are reliant on winter rainfall.

    Its the variability in winter from one year to the next that needs to be elucidated and we need to ask Variability from what source, what mechanism. China is currently experiencing the coldest winter for 30 years. Surface pressure is very high from Greenland/Hudsons Bay through to Southern China. Arctic air is streaming south. It descends form above. See here: http://earth.nullschool.net/#current/wind/surface/level/overlay=misery_index/orthographic=-77.62,90.62,430/loc=121.742,61.972

    The balance between surface pressure in high versus mid latitudes is the essence of the Arctic Oscillation also known as the North Atlantic Oscillation. Its this phenomenon that determines whether people in the mid latitudes experience warm moist westerly winds or cold dry Arctic blasts. And, its strictly a winter variability thing that relates to the presence of ozone that initiates and drives Polar Cyclone activity. If there is more ozone aloft then surface pressure falls in high altitudes and the warm moist westerlies are drawn further northwards. This is primarily a northern hemisphere thing. Next post will show that variability in the mid latitudes of the southern hemisphere is slight by comparison.

    So, the nature of the ‘forcing’ that is being applied is critical. I see that forcing as being intimately associated with the movements of the air, the planetary winds and cloud cover mediating the amount of solar radiation reaching the surface.


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