About Meridional Cooling and Climate Change

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Fig. 7.1. Changes in the Atlantic Multidecadal Oscillation and solar activity are consistent with temperature changes. Top, above average solar activity reduces poleward transport causing warming. Bottom, the ascending half-period of the Atlantic Multidecadal Oscillation causes an even bigger reduction in transport and has a bigger temperature effect. Middle, temperature evolution for the past 120 years is consistent with the effect of these two factors on transport. Data from SILSO sunspots (top), HadCRUT4 deseasonalized temperature (middle), and AMO deseasonalized (bottom), have been smoothed with a gaussian filter.

A recent post was Seven Theories of Climate Change, summarizing an array of explanations for fluctuations in temperatures and precipitation over Earth’s surface. Now, thanks to Javier Vinós & Andy May, we have a new hypothesis combining solar variability with oceanic/atmospheric oscillations to explain the climate record. An introduction to their findings is published at Climate Etc. The Winter Gatekeeper Hypothesis (VII). A summary plus Q&A. Excerpts in italics with my bolds and some added images. My first exposure to meridional cooling was provided by Clive Best, and later on is a repost of that understanding consistent with Vinós & May.

A synopsis of the Winter Gatekeeper hypothesis

The IPCC assessment reports published since 1990, reflect a scientific consensus that natural forces, including solar activity and ocean-atmosphere oscillations, like the Atlantic and Pacific multidecadal oscillations, had a net zero effect on the observed global average surface temperature changes since 1951. The IPCC consensus does not allow for changes in the poleward (meridional) transport of energy to have significantly affected this average temperature over the past 75 years.

The Winter Gatekeeper hypothesis proposes that changes in the meridional transport of energy and moisture are the main way the climate changes now and in the past.

Meridional transport variability has many causes and forces that act simultaneously and in different time frames on the climate system. They integrate into a very complex poleward energy transportation system. Among these are multidecadal ocean-atmosphere oscillations, solar variability, ozone, stratospheric-reaching tropical volcanic eruptions, orbital changes, and changing luni-solar gravitational pull. Meridional transport is therefore an integrator of internal and external signals.

It is not the only way the climate changes, but evidence suggests it is the main one.

The Winter Gatekeeper hypothesis does not disprove greenhouse gas effect induced climate change—manmade or otherwise—in fact, it acts through it. But it does not require changes in the atmospheric content of non-condensing greenhouse gases to cause significant climate change. Therefore, it does refute the hypothesis that CO2 is the main climate change control knob.

Meridional transport moves energy that is already in the climate system toward its exit point at the top of the atmosphere at a higher latitude. It is carried out mainly by the atmosphere, in both the stratosphere and troposphere, with an important oceanic contribution. The greenhouse effect is not homogeneous over the planet due to the unequal distribution of water vapor, and it is stronger in the wet tropics, weaker over deserts, and much weaker at the poles in winter. When meridional transport is stronger, more energy reaches the poles. There it can more efficiently exit the climate system, particularly during the winter, when there is no Sun in the sky. Most polar imported moisture in winter freezes, emitting its latent heat. Additional CO2 molecules increase outward radiation, as they are warmer than the surface. The net result is that all imported energy into the polar regions in winter exits the climate system at the top of the atmosphere (Peixoto & Oort, 1992, p. 363), and increasing the energy transported there at that time can only increase the loss.

When meridional transport is stronger, the planet loses more energy and cools down (or warms less) in a non-homogeneous way, because the net energy loss is greater in the polar regions. However, as more energy is directed toward the poles, the Arctic region warms, even as the rest of the world cools or warms more slowly. When meridional transport is weaker, less energy reaches the poles and exits the climate system. Then the planet loses less energy and warms, while the Arctic cools, because it receives less energy from the lower latitudes.

Figure 12: The effect of strong and weak Atlantic THC. Idealized portrayal of the primary Atlantic Ocean upper ocean currents during strong and weak phases of the thermohaline circulation (THC) Source: Bill Gray: H20 is Climate Control Knob, not CO2

Most of the energy is transported through the lower troposphere and ocean track. As a result, changes in multidecadal ocean oscillations produce a greater effect on climate in the multidecadal timeframe than changes in solar activity. Solar changes have a stronger effect on stratospheric energy transport. Even so, there is a non-well-defined link between changes in solar activity and changes in the multidecadal oscillations that result in major multidecadal climate shifts right after 11-year solar cycle minima (see Part IV). Nevertheless, modern global warming started c. 1850, when the Atlantic Multidecadal Oscillation increased its amplitude and period (Moore et al. 2017). The overall multidecadal oscillation (aka the stadium wave) currently has a period of c. 65 years, and the 20th century included two rising phases of the oscillation, explaining its two warming phases (1915-1945, and 1976-1997; Fig. 7.1).

Meridional transport was further reduced during the 20th century by the coincidence of the Modern Solar Maximum (Fig. 7.1 at top): A long period of above average solar activity between 1935 and 2004. It is the longest such period in at least 600 years. Solar activity acts mainly on stratospheric energy transport, but since it affects the strength of the polar vortex and the El Niño/Southern Oscillation (see Part II), it also influences tropospheric transport.

As it can be seen in Fig. 7.1, most of the warming during the 20th century can be explained by the combined effect of the ocean multidecadal oscillations and the Modern Solar Maximum on meridional transport. No other proposed factor can satisfactorily explain the early 20th century warming period, the mid-20th century shallow cooling, and the late 20th century strong warming period, without resorting to ad-hoc explanations. In a single century two periods of reduced transport (warming), coincided with the ascent of the Atlantic Multidecadal Oscillation and the effect of the modern solar maximum.

This resulted in 80 years of diminished transport that contributed to the greatest warming in 600 years, triggering political and scientific alarm.

Background Post Arctic “Amplification” Not What You Think

HT to Dr. David Whitehouse writing at GWPF regarding a recent study claiming Arctic Amplification is causing a wavey polar vortex, resulting in winter warming and cooling extremes.  His critique is Extreme cold snaps and global warming: A speculative explanation.

This post is challenging the notion of Arctic Amplification itself.  The term is bandied about with the connotation that man-made global warming is multiplied in the Arctic and responsible for weather extremes.

As the animation above shows, there have been in recent years alternating patterns of unusually cold or warm weather in the Northern Hemisphere.  There are several problems in the attempt to link these events to global warming/climate change, i.e., claiming causation from a slow increase in baseline global average temperatures.

  1. Arctic Amplification is an artifact of Temperature Anomalies
  2. Arctic Surface Stations Records Show Ordinary Warming
  3. Arctic Warmth Comes from Meridional Heat Transport, not CO2


1. Arctic Amplification is an artifact of Temperature Anomalies

Beyond the issues with the measurements and the questionable adjustments, there is a more fundamental misconception about air temperatures in relation to “climate change.” Clive Best does a fine job explaining why Global Mean Temperature anomalies do not mean what people think. Below is my synopsis of his recent essay entitled Do Global Temperatures make sense? (link)

Background: Earth’s Heat Imbalance

ERBE measurements of radiative imbalance.

The earth’s temperature at any location is never in equilibrium. It changes daily, seasonally and annually. Incoming solar radiation varies enormously especially near the poles which receive more energy per day in summer than the equator.

The earth cools primarily by moving heat from hot tropical regions towards high latitudes where net IR radiation loss cools the planet, thus maintaining a certain temperature profile.

Key Point: GMT Anomalies Are Dominated by the Highest Latitudes

The main problem with all the existing observational datasets is that they don’t actually measure the global temperature at all. Instead, they measure the global average temperature ‘anomaly’. . .The use of anomalies introduces a new bias because they are now dominated by the larger ‘anomalies’ occurring at cold places in high latitudes. The reason for this is obvious, because all extreme seasonal variations in temperature occur in northern continents, with the exception of Antarctica. Increases in anomalies are mainly due to an increase in the minimum winter temperatures, especially near the arctic circle. 

To take an extreme example here is the monthly temperature data and calculated anomalies for Verkoyhansk in Siberia. Annual temperatures vary from -50C in winter to +20C in summer. That is a seasonal range of 70C each year, and a year-to-year anomaly variation of ~8C is normal. The only global warming effect evident is a slight increase in the minimum winter temperatures since 1900. That is not due to any localised enhanced greenhouse effect but rather to an enhanced meridional heat transport. Temperatures in equatorial regions meanwhile have only ~4C seasonal variations and show essentially no warming trend.

2. Arctic Surface Stations Records Show Ordinary Warming

Locations of 118 arctic stations examined in this study and compared to observations at 50 European stations whose records averaged 200 years and, in a few cases, extend to the early 1700s

A recent extensive analysis of Northern surface temperature records gives no support for Arctic “amplification” fears.

The Arctic has warmed at the same rate as Europe over the past two centuries. Heretofore, it has been supposed that any global warming would be amplified in the Arctic. This may still be true if urban heat island effects are responsible for part of the observed temperature increase at European stations. However, European and Arctic temperatures have remained closely synchronized for over 200 years during the rapid growth of urban centres.

And the warming pattern in Europe and the Arctic is familiar and unalarming.

Arctic temperatures have increased during the period 1820– 2014. The warming has been larger in January than in July. Siberia, Alaska and Western Canada appear to have warmed slightly more than Eastern Canada, Greenland, Iceland and Northern Europe. The warming has not occurred at a steady rate. Much of the warming trends found during 1820 to 2014 occurred in the late 1990s, and the data show temperatures levelled off after 2000. The July temperature trend is even slightly negative for the period 1820–1990. The time series exhibit multidecadal temperature fluctuations which have also been found by other temperature reconstructions.

The paper is: Arctic temperature trends from the early nineteenth century to the present W. A. van Wijngaarden, Theoretical & Applied Climatology (2015).  My synopsis: Arctic Warming Unalarming

3. Arctic Warmth Comes from Meridional Heat Transport, not CO2

Key Point: Heat Distribution Changes, not Global Temperatures

Rising CO2 levels modify that radiation imbalance profile slightly. Surface temperatures in the tropics are not really warming at all. Any excess heat induces more clouds and more convection while surface temperatures remain constant. What really happens is that the meridional radiation profile changes. Slightly more heat is transported polewards so that hot places are shifting more heat to cold places which are doing the warming. If CO2 levels stop rising, then a new temperature and radiation profile would rather quickly be reached. This is then called ‘climate change’ but any such changes are concentrated in colder regions of the world. The global ‘temperature’ itself is not changing, but instead the global distribution of temperature is changing.

Key Point: More Atmospheric Heat means Warming in the Coldest Places

Temperatures at the poles during 6 months of darkness would fall well below -150C if there was no atmosphere, similar to the moon. Instead, heat is constantly being transported from lower latitudes by the atmosphere and ocean and so that temperatures never fall much below -43C. If more heat is transported northwards than previously, then minimum temperatures must rise, and this is what we observe in individual measurements.

Long term changes in temperature anomalies occur mainly in northern continents in winter months. This is not because the earth as a whole is warming up but rather that meridional heat transport from the equator to the poles has increased and the largest effect on ‘anomalies occur in winter. The average absolute temperature of the earth’s surface is unknown. Basing the evidence for climate change on the 150-year trend in global averaged temperature anomalies still biases the result towards higher latitudes where most of the stations are located.


When heat is released into the atmosphere from the oceans, it is transported toward the poles to dissipate into space. Places in higher latitudes are warmed, not by radiative effects of greenhouse gases in those locales, but by the incursion of warmer air from the equator.

What happens if more CO2 is added into the atmosphere? No one knows, but there are many opinions, a popular one being that more heat is retained in the atmosphere. But in that case, that additional heat will be shed by the planet in exactly the same manner: transport to the poles with slightly less extremely cold air at the higher latitudes.

Why in the world would we pay anything to prevent a little bit of warming in the world’s coldest places?

Clive Best takes the analysis further and relates to work by Christopher Scotese in a later post Fact: Future Climate Will Be Flatter, not Hotter

More explanation at The Climate Water Wheel

Resources:  Bill Gray: H20 is Climate Control Knob, not CO2

No, CO2 Doesn’t Drive the Polar Vortex (Updated)

Quantifying Natural Climate Change

via Science Matters

September 23, 2022

About Meridional Cooling and Climate Change | Science Matters (rclutz.com)

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