A Tale of Two Climatic Changes: Part Three
Key to understanding the posts is Earth’s power balance as presented by Nobel-laureate Dr John Clauser in a video
Clauser concludes that Earth’s temperature should remain relatively constant thanks to a cloud thermostat that buffers power density changes of up to 18 W/m2, so humankind should not be worried about the relatively minor power density increases caused by atmospheric CO2 increases.
But he leaves open the question on what physical process can disrupt this power balance and cause ‘climate change’. Clauser’s zero-sum zero-dimensional power balance (below) does not take into account temporal and regional power density differences and shifts, and does not take into account a “Stored Ocean Heat” term that has demonstrably played a role in Earth’s recent global warming.
The North Atlantic’s Semi-permanent climate systems
Post 1 documented the substantial difference between the glacial to interglacial transition – severe climate change – to the comparably minor “climate change” we are currently experiencing. During the glacial to interglacial transition large regions experienced temperature increases of up to 35 ºC, and cold climate zones migrated dramatically to higher latitudes, e.g. Western Europe shifted from a cold, dry Tundra to a warm, wet Temperate climate.
This climatic change was caused by a systemic shift of the semi-permanent European and North American weather systems. North Atlantic Low Pressure systems (LG: Low Glacial, LI: Low Interglacial) remained at the Polar Front, that is at the boundary between the Polar and Ferrel Cells.
However the semi-permanent High Pressure systems shifted from over the ice sheets (HG: High Glacial), that is from within the Polar Cell, to the Azores/Bermuda high, at the boundary between Ferrel and Hadley Cells, where the large-scale downward circulation of relatively cool, dry air increases atmospheric pressures.
What has been causing our recent “climate change”?
Our current “climate change” has been comparably minor. Temperature changes of a few degrees and precipitation changes of a few mm over the course of the last few decades have not caused significant regional reclassifications under the Köppen-Geiger Climate Classification system.
Small changes in precipitation and temperature can occur as a result of changes within the semi-permanent weather systems. For example, the 1951-1980 average January temperature in The Netherlands was around 2 ± 2 ºC.
This relatively mild and constant average January temperature is largely due to the stability of the Azores high – Icelandic Low pressure systems, which under average conditions generate relatively warm, westerly winds in winter.
When the high-low pressure difference is small these westerly winds become weaker, which opens the door for colder, continental weather systems to dominate and lower Dutch temperatures. This is basically what happened in 1963: the Azores High – Iceland Low pressure difference became abnormally small: the NAO Index dropped to -2.12 whereupon the average January temperature dropped to -5.6 ºC.
Fluctuations in the North Atlantic Azores – Iceland pressure difference are termed the “North Atlantic Oscillation”, which is demonstrably one of the most important causes of decadal climate fluctuations in the North Atlantic (https://www.science.org/doi/10.1126/science.269.5224.676).
“Over the past decade [the article was published in 1995], the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry
conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.”
NOAA monitors the North Atlantic Oscillation (NAO) via an index (graph above; https://www.ncei.noaa.gov/access/monitoring/nao/). High index values represent large pressure differences,
which in turn are associated with above-normal temperatures in the eastern United States and across northern Europe, above-normal precipitation over northern Europe and Scandinavia, and below-normal precipitation over southern and central Europe. Opposite patterns of temperature and precipitation occur during low values of the index, i.e. during periods when the pressure difference is small.
NOAA’s Winter (Jan,Feb) NAO Index data confirm the “coherent large-scale changes since 1980” that Hurrell in 1995 (https://www.science.org/doi/10.1126/science.269.5224.676) concluded were “contributing significantly to the recent wintertime warmth across Europe”: the 30 percent-smoothed LOESS line (left graph above) shows a lower-than-average 1950-1979 period, followed by a higher-than-average post-1980 period. (data: https://psl.noaa.gov/data/20thC_Rean/timeseries/monthly/NAO/nao.20crv2c.long.data)
Systemically above-average NAO Index variability correlate well to the NASA-reported (https://data.giss.nasa.gov/gistemp/graphs_v3/) 1910-1940 and post-1980 global mean surface temperature increases, as well as the 1950-1960 decrease.
So we’ve peeled back another layer of the onion. What is causing our current minor “climate change” in the Northern Atlantic? It must to a significant extent be due to the systemic increase of the NAO index, which in turn is the result of the growth and intensification of the semi-permanent Azores/Bermuda High and Icelandic Low pressure systems.
A systemic increase in the NAO index caused “above-normal temperatures in the eastern United States and across northern Europe, above-normal precipitation over northern Europe and Scandinavia, and below-normal precipitation over southern and central Europe”. But what’s causing this systemic increase?
Why is the Azores/Bermuda high growing and intensifying?
The IPCC AR5 noted great similarities between the 1910-1940 and post-1980 warming periods: “the most pronounced warming [occurs] in the Arctic during the cold season, followed by North America during the warm season, the North Atlantic Ocean and the tropics.”
A look at the NASA temperature reconstructions (https://earthobservatory.nasa.gov/world-of-change/global-temperatures) helps clarify whether a growing and intensifying Azores high is a likely cause of the 1910-1940 North Atlantic warming.
Around 1900-1904 the North Atlantic temperature anomaly map shows only minor differences from NASA’s 1951-1980 baseline. By 1935-1939 however significant warming had occurred in the North Atlantic ocean under the Azores/Bermuda high.
This heat is delivered to the weather systems that share it with the North American and European onshore. The geographical correlation of the 1935-1939 North Atlantic temperature anomaly with
the Azores/Bermuda high is almost certainly not fortuitous.
High pressure systems are caused by large-scale downward circulation of relatively cool, dry air, which thereby suppresses the upward convection of heat.
This same process causes heatwaves: a lingering high pressure system delays the upward convection of heat. When the Azores High’s pressure increases due to an increase in downward circulation of air, it further suppresses upwardly convecting heat, forcing heat to accumulate in the North Atlantic atmosphere and ocean.
A cartoon (https://pilotinstitute.com/high-vs-low-pressure-systems-explained/) demonstrates how this process also moots the cloud-thermostat and regionally disrupts the power balance: the relatively cold, dry downwards flow of air in high pressure systems results in relatively cloud-free conditions over the high, and therefore causes the cloud-thermostat to malfunction.
n the long term this accumulated ocean heat will counteract the high pressure expansion: by 1960-1964 the Azores/Bermuda high area (NAO Index graph above) and the North Atlantic temperatures (NASA map) were back to “normal”.
The 2015-2019 NASA map demonstrates similar processes are at work in the present day. The strengthening Icelandic low pressure system is the only North Atlantic area where no significant heat has accumulated over the last 124 years, very likely due to its efficient upward convection of heat: the warm, humid upward movement of air over the intensifying low pressure system convects heat up to the Tropopause, where it can effectively be radiated to space.
So we’ve peeled back another onion layer. What caused the 1910-1944 and present North Atlantic warming? The growth of the Azores / Bermuda high resulted in the accumulation of atmospheric and ocean heat under the high. But what caused the Azores / Bermuda high to grow and intensify?
The Azores High growth could plausibly be due to the strengthening of the Hadley Cell to the south, although this is rather unlikely, as the temperature over the tropics has remained relatively constant (1935-1939 and 2015-
2019 maps) due to the cloud-thermostat enforcing the Cell’s stability. In addition, the strengthening of the Icelandic Low strongly indicates it’s almost certainly the mid-latitude Ferrel Cell that is strengthening.
The Arctic Cell
The 1935-1939 and 2015-2019 NASA maps demonstrate that during both periods of North Atlantic warming the Arctic was heating 2-4 times faster than the mid-latitudes. Recent studies (https://link.springer.com/article/10.1007/s00382-016-3067-x) have demonstrated the existence of an “Arctic Cell“ (“A” in figure b above), whereby “there is a significant negative correlation between the Arctic and Polar cell strengths.
” The Arctic Cell grows in strength during the winter months, i.e. during the months the Azores high is forming. The figure below demonstrates that Arctic Cell growth is accompanied by Ferrel Cell strength increase during the winter months. i.e. when the Azores high is forming and strengthening.
The Arctic Cell strengthens as a function of Arctic temperature: higher Arctic temperatures cause more heat to be radiated to space via the Arctic Low.
Conclusion Post 3:
The 1910-1944 and recent North Atlantic warming periods were caused by a growing and intensifying Azores High, which in turn was caused by a strengthening Ferrel Cell, which in turn was caused by a strengthening Arctic Cell, which in turn was caused by increases in Arctic temperatures.
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