Cycles
posted 2nd June 2020
We know that the Earth has gone through many different cycles during its existence. The Earth has experienced ice ages, where it has been (almost) completely cover in ice, and periods of inter-glacial, where there has been no ice. These cycles are completely natural and occurred long before humans evolved on the planet and are still occurring today. As we have about 24mKm2 of ice at present, we are technically still in an ice age.
There are numerous cycles, solar, atmospheric, and oceanic which affect our planet. Each cycle varies in magnitude and time frame and many interact with others.
Milankovitch Cycles:
Let us start with Milankovitch Cycles: Milankovitch was a scientist, born in Croatia in 1879. His work was studying how the Earth's movement and position in relation to the sun and how this changed the climate of the Earth.
Fig 1 Milankovitch Cycles with addition of Vostok ice core data and benthic forams
[Milankovitchhttps://en.wikipedia.org/wiki/Milankovitch_cycles]
- Orbital eccentricity - based on the Earth's elliptical orbit and has a cycle of ~100,000 years
- Axial Tilt (obliquity) - ranges between 22.1° and 24.5° over a cycle of ~42,000 years
- Axial precession - is the direction of the Earth's axis or rotation relative to fixed stars with a cycle of ~26,000 years
- Apsidal precession - the orbital ellipse precesses in space with a cycle of ~112,000 years. Within this cycle there is also a ~26,000 years cycle.
Milankovitch considered, obliquity as the most prominent of these cycles. Measurements from the Vostok Ice Core data shows the ~112,000-year cycles very well.
Fig 2 Vostok Ice Core data showing the ~100,000 year obliquity cycles
Vostock
Vostok Ice Core
The cycle of benthic foraminifera are a form of plankton abundant in the oceans. They have been used to measure climatic changes and appear to align with the Vostok ice core data. They increase after a rise in temperature then a rise in CO2, which makes sense as they photosynthesise.
Vostok Ice Core
On the subject of the sun, it also goes through cycles of roughly 11 years, when solar activity, the number of sunspots, solar flares and coronal loops affect weather an ultimately climate on Earth.
Solar Cycles:
The relationship between sunspots and the temperature of the Earth is reasonably well understood, with more sunspots the Earth becomes warmer and lower sunspots the Earth becomes cooler although the time lag is not fully understood.
There has been a lessening of the last three solar cycles, with the early Cycle 25 showing no difference to the downward trend.
Fig 3 shows the cycles of sunspot activity.
Solar Cycles
Ocean cycles:
El Nino Southern Oscillation (ENSO):
El Nino is the warm phase of the ENSO oscillation and La Nina the cool phase. These phases are depicted by warm/cool sea surface temperatures (SST) off the east coast of South America in the Pacific Ocean. These effects are shown globally in atmospheric temperatures. ENSO is the most important of the ocean cycles having the strongest effects on global temperatures.
Fig 4 shows El Nino and La Nina events from 1950 -2015
ENSO
Since satellite temperature records began in 1979 University Alabama Huntsville (UAH) has been recording lower atmosphere temperatures. These show up some recent ENSO, El Nino's of 1998, 2016 and 2019/20 in particular. The latest data figure 5, from April 2020 shows the start of a downward trend.
Fig 5 UAH Satellite Lower Atmosphere Δ Temperature 1979-2020
UAH
The downward trend aligns with the latest ENSO index 02Jun2020
UAH satellite Lower Troposphere Temperature
PDO
Pacific Decadal Oscillation (PDO):
The Pacific Decadal Oscillation affect sea surface temperatures (SST) north of 20°N and range between warm and cool over a period of roughly 20-30 years.
Fig 7 shows the warmer and cooler cycles of the PDO
[PDO=http://www.chanthaburi.buu.ac.th/~wirote/met/tropical/textbook_2nd_edition/navmenu.php_tab_5_page_3.1.0.htm
The PDO appears to be entering a cool phase in line with the solar cycles.
Atlantic Multidecadal Oscillation (AMO):
The North Atlantic Multidecadal Oscillation: The area of the north Atlantic Ocean goes through cycles of warm and cold surface sea temperatures (SST). The fluctuations are irregular based on interdecadal variations. The AMO has a cycle periodicity of ~60 years (30 years warms and 30 years cool). This cycle is about to change to cool phase.
Fig 8 shows the Sea Surface Temperature anomalies of the AMO warm/cool phases.
AMO
Summary of Ocean Oscillations:
ENSO, PDO and AMO are the three main ocean oscillations, there are several, less dominant ones, such as the Arctic Oscillation (AO or NAM), Interdecadal Pacific (IPO), Madden-Julian Oscillation (MJO) and the Quasi-biennial Oscillation (QBO).
ENSO is in a neutral phase, tending to La Nina (cooler). The PDO is tending to cooling phase and AMO is about to change to its cool phase. Along with the low solar cycle, it makes for interesting times.
Atmospheric Cycles:
The Inter-Tropical Convergence Zone (ITCZ): it is depicted by a line of cloud, mainly cumulonimbus, encircling the Earth near the Equator. This produces heavy rainfall.
It oscillates between 500km-4,000km north and south (either side of the Equator) depending on season. The ITCZ also has connections to monsoon formation affecting the Indian Ocean and sub-continent.
Fig 9 The Inter-Tropical Convergence Zone
ITCZ
The Jet Streams:
There are two main Jet Streams, one which circulates the Norther Hemisphere and is mainly runs in a West to East direction. The other is positioned in the Southern Hemisphere and also runs West to East. These are known as the polar jet streams. There are two other jet streams known as the sub-tropical jet streams and occur both north and south of the equator.
These jet streams occur mainly between 20,000 and 40,000ft in the atmosphere. They normally vary in strength from about 40-200Kts. Aircraft pilots use these Jet Stream to plan routes, greater tail winds helps to shorten flight times and increases fuel efficiency.
It is common for low-pressure systems to follow the line of the jet streams. The position of all jet streams are erratic in position and strength.
They have an enormous effect on weather.
Fig 10 Northern Jet Stream 02Jun2020
Northern Jet Stream
Fig 11 show the polar and southern sub-tropical Jet Stream 02Jun2020
Southern Jet Streams
Summary of Cycles:
We have seen there are a multitude of different natural cycles and oscillations, which affect different aspects of weather and hence ultimately climate on Earth. The big question is, does anybody know how they all interact with each other or does it simply lead to the chaotic effect on weather and ultimately climate?
Given the latest information in the figures shown in this article, there appears to be a downward trend in temperature shown by all the key cycles of ENSO, the PDO the AMO and Solar Cycle. I wonder when the last time all these cycles started going negative, perhaps it was during the Maunder Minimum!
Considering the Inter-governmental Panel on Climate Change (IPCC) "The climate system is a coupled non-linear chaotic system" begs the question, is the climate system possible to fully understand?
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