Here is more evidence  of an exceptionally deep solar minimum which will arrive around 2020. For the last three days, the irreplaceable and invaluable Spaceweather.com has been alerting us to it. These signs of an unusually deep solar minimum have important implications about global warming.

The Evidence of  Sunspot Numbers for a Deep Solar Minimum

Several posts back,  I wrote of other evidence cited by Spaceweather.com about a coming deep solar minimum. The evidence noted there was given by the unusually small number of sunspots for this phase of the solar cycle. Space weather.com wrote,

The sun is spotless again. For the 133rd day this year, the face of the sun is blank.To find a year with fewer sunspots, you have to go back to 2009 when the sun was experiencing the deepest solar minimum in a century.

The number of sunspots existing at a particular time is directly related to the total power output of the Sun. The more power the Sun generates, the more sunspots we will see. This power output varies over a well known eleven year cycle appropriately called the solar cycle. Although there is evidence for solar cycles stretching back around 11,400 years, people started numbering solar cycles in 1755, with solar cycle 1 beginning February of that year. We are now approaching the end of solar cycle 24, which should occur around 2020. A graph of sunspot numbers over time for the last three solar cycles is shown below.

Notice the peaks of sunspot numbers have been decreasing ever since the 1990s. This appears to be connected to the “pause” in global warming we have seen since the late 1990s. This correlation will be discussed more later.

A New Index For Solar Irradiance of Earth Predicts a Deep Solar Minimum

However,  we now have a different and independent indication of the approach of an unusually deep solar minimum. Called the “Thermosphere Climate Index” (TCI), it gives how much heat is being radiated into space from NO molecules in the thermosphere. The thermosphere is the next to last layer of the atmosphere before you get to interplanetary space. Its temperature is extremely sensitive to solar irradiance, the power per unit area received from the Sun. The higher the solar irradiance, the hotter the molecules in the thermosphere become. The higher the temperature of thermosphere NO molecules, the more those molecules will reradiate energy back into space. Ipso facto, the greater solar activity becomes, the higher Earth’s TCI becomes.

Notice the value of the TCI is primarily a measure of how large the solar irradiance of Earth is, i.e. how active the Sun is. It says almost nothing directly about how hot the bottom layer of the atmosphere, the troposphere, is. The troposphere holds around 75% of the atmosphere’s total mass and 99% of the total mass of atmospheric water and aerosols. It is where weather lives. However, the TCI does have some indirect implications for global warming, which will be discussed in the section about global warming below.

So what is the TCI telling us now? Spaceweather.com quotes Martin Mlynczak of NASA’s Langley Research Center as saying:

We see a cooling trend. High above Earth’s surface, near the edge of space, our atmosphere is losing heat energy. If current trends continue, it could soon set a Space Age record for cold.

Martin Mlynczak also stated,

The thermosphere always cools off during Solar Minimum. It’s one of the most important ways the solar cycle affects our planet.

Mlynczak states that as the end of 2018 approaches, the TCI is close to setting a record for cold. He declares, “We’re not there quite yet, but it could happen in a matter of months.”

Below is a plot of the TCI from 1947 to 2016 that was recently published in the paper

Mlynczak, M. G., L. A. Hunt, J. M. Russell III, B. T. Marshall, C. J. Mertens, and R. E. Thompson (2016), The global infrared energy budget of the thermosphere from 1947 to 2016 and implications for solar variability, Geophys. Res. Lett., 43, 11,934–11,940, doi: 10.1002/2016GL070965.

If you compare the last three solar cycles from this plot with the plot of sunspot numbers, you can see they march together almost in lockstep. They both predict a particularly deep solar minimum.

The Implications For Global Warming

So,  what does all this have to do with global warming, particularly with the controversy over Anthropogenic Global Warming (AGW)? Measures that show how active the Sun is do little to show us directly how the troposphere’s temperature might vary. The variations in solar irradiance are just too small.

However, there is a very strong, indirect influence of solar activity on global warming. By now the mechanism by which solar activity affects global temperatures has been well established observationally, experimentally, and theoretically. I will call it the solar wind-cosmic ray-cloud cover mechanism,  or SCCM for short.

First, there is the fact that a very active Sun is the source of an intense solar wind. As the Sun becomes less active approaching a solar minimum, the solar wind becomes progressively less intense.

Second, we have known for a very long time that the solar wind sweeps cosmic rays away from the inner solar system. Cosmic rays are extremely high energy particles — mostly protons — that originate from outside the solar system. When the Sun is very active, its intense solar wind limits the number of cosmic ray particles that can reach Earth. When the Sun is less active, the solar wind becomes less intense and more cosmic ray particles can reach us.

In general, cosmic ray particles are more energetic than particles in the solar wind, but less dense. Because they are more energetic, they can penetrate deeper into our atmosphere than the solar wind and ionize atmospheric particulates. These ionized particulates act as nucleation centers that attract water molecules to form clouds.

As the solar cycle approaches a minimum, the planetary cloud cover becomes greater. Clouds act to cool the planet by reflecting incident solar radiation back into space.

That is the basic theoretical explanation for SCCM. It was first conceived in 1996 by a Danish physicist by the name of Henrik Svensmark. Svensmark and his team from the National Space Institute at the Technical University of Denmark (DTU Space) collaborated with the Racah Institute of Physics at the Hebrew University of Jerusalem to demonstrate the solar wind-cloud cover connection. Together, they showed the linkage of changes in the solar wind to Earth’s cloud cover using 25 years of satellite data. In 2016 they published their results in the peer-reviewed Journal of Geophysical Research. Its exact citation is

J. Svensmark, M. B. Enghoff, N. J. Shaviv, H. Svensmark. The response of clouds and aerosols to cosmic ray decreases. Journal of Geophysical Research: Space Physics, 2016; DOI: 10.1002/2016JA022689

If you click on the link in the citation, you can get a full copy of the paper, although you will have to pay for the privilege! A fascinating video of Svensmark’s tribulations in forming the SCCM is embedded below.

Finally, there was experimental verification of the model from a CERN cloud chamber experiment. In collaboration with Svensmark, a CERN team headed by Dr. Jasper Kirkby demonstrated that an atmosphere with typical concentrations of typical aerosol particulates and exposed to typical intensities of cosmic rays would create cloud nucleation centers in the requisite densities. They published in the peer-reviewed journal Science, with the citation

Riccobono et. al., “Oxidation Products of Biogenic Emissions Contribute to Nucleation of Atmospheric Particles”, Science, vol. 344, Issue 6185, pp. 717-721, 16 May 2014.

With the complexity of the phenomenon of global warming, you can be well assured the SCCM is only a piece — albeit a rather large one — of the total puzzle. Consult the plot of the Thermosphere Climate Index one more time. The warming phase of the SCCM is associated with the rising peaks of the solar maxima during solar cycles 20, 21, and 22. This covered the years from sometime in the middle 1970s to sometime in the middle to late 1990s. The cooling phase of SCCM is shown by the falling peaks during solar cycles 22, 23, and 24. This phase started in the late 1990s and should end around 2030. Altogether, the length of a warming phase or cooling phase is very roughly 35 years. Yet we know the Earth has been warming on average since the end of the Little Ice Age in the middle of the 19th century. Below is a plot produced by NOAA of global “temperature anomalies” from 1880 to 2014. The globally averaged planetary temperature for a particular year is the surface temperature averaged over the entire globe and then averaged over the year. If you find the average of these globally averaged temperatures between the years 1901 and 2000, you obtain NOAA’s baseline temperature. Subtracting that base line temperature from any year’s globally averaged temperature yields that year’s temperature anomaly. That is what is plotted below.

One can criticize this data on several grounds (note the large error bars for years before 1945), but I think it shows overall trends correctly. They coincide with trends from independent data sets of globally averaged temperature anomalies. Clearly, the trend over the last one-and-a half centuries has been overall warming. Could this overall warming be the result of human emissions of carbon dioxide?

Actually, it is physically impossible for CO₂ to be responsible for the overall warming. The primary reason is the very tiny fraction of the atmosphere (around 0.0004) that is carbon dioxide. Atmospheric carbon dioxide is also almost totally saturated with infrared radiation already and can absorb no more. These and other facts are described in much greater detail in the following posts.

• Thermodynamic Interactions of the Oceans With the Atmosphere
• Thermodynamic Effects of Atmospheric Carbon Dioxide Revisited
• CO2 Levels In Air Dangerously Low for Life on Earth

If human-emitted CO₂ is not the explanation, what is? As it turns out, we can give a name to the explanation, but we do not truly understand it. The name is the Dansgaard-Oeschger cycles. These are cycles of warming and cooling with a half-period of warming or cooling lasting very roughly about 500 to 600 years. We are now in the warming phase, which should last to sometime around 2400. The previous cooling phase was the Little Ice Age, lasting from sometime around 1300 to sometime in the middle 1800s. The actual dating is very uncertain, as is the cause. The previous warming phase was the Medieval Warm Period, occurring roughly between the years 950 and 1250. Because the Medieval Warm Period and the Little Ice Age happened before large scale industrialization, we can be sure these cycles are not caused by human emissions of CO₂.

From the temperature anomaly plot above, we can see the sum of the Dansgaard-Oeschger warming and the cooling phases of the SCCM almost cancel each other during the warming pauses of 1940-1975 and of c. 1999 to the present. During the warming periods of c.1915 to 1940 and of 1975 to the late 1990s, the two phenomena reinforce each other to give overall warming.

In none of this history do we require man-produced carbon dioxide to explain what is observed.

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