onsdag 3. februar 2021

Solar activity and Global temperature

We know how the number of sunspots has varied since before the industrial revolution. Satellites have measured the total solar irradiance at the top of the atmosphere since the late 1970s. There is a strong positive correlation between the number of sunspots and the solar irradiance. The number of sunspots is therefore a good proxy when estimating the solar irradiance before the satellite era. 

NOAA summarizes the connection between solar irradiance and global temperature on their web site: 'If the Sun were to intensify its energy output then, yes, it would warm our world. Indeed, sunspot data indicate there was a small increase in the amount of incoming sunlight between the late 1800s and the mid-1900s that experts estimate contributed to at most up to 0.1°C of the 1.0°C (1.8°F) of warming observed since the pre-industrial era. However, there has been no significant net change in the Sun’s energy output from the late 1970s to the present, which is when we have observed the most rapid global warming.'

The three figures in this blog post are based on monthly values that are updated up to and including December 2020.

Solar intensity and sunspots

The solar intensity varies by approximately 0.1 per cent over a solar cycle. Both the variations and the average value of the intensity differ a little from one cycle to the next. A solar cycle lasts on average for just over 11 years.

Figure 1 shows the solar irradiance and the number of sunspots since the mid-1880s. It covers a little more than 12 solar cycles.  Appendixes A.1 and A.2 explain from where the Total Solar Radiance and the Sunspot numbers are downloaded.

Figure 1: The blue curve shows how the solar intensity has varied since the mid-1880s. It refers to the blue values on the left y-axis, which is the Total Solar Irradiation in Watts per square meter. The red curve shows the number of sunspots. The curves are based on monthly values that are smoothed by calculating the average over 36 months.

The figure shows the strong positive correlation between sunspot numbers and the solar irradiation. It also shows that the solar irradiance has slightly decrease since about 1960.

fredag 1. januar 2021

Solar Cycle Model failed totally when predicting colder temperatures

To download the blog post as a pdf file, click here.


Jan-Erik Solheim, Kjell Stordahl and Ole Humlum (hereafter SSH) published two articles in 2011 and 2012 about the relationship between the mean temperature in a solar cycle and the length of the previous solar cycle [1, 2]. For the northern hemisphere, they found a negative correlation between those two variables. A long solar cycle is followed by one with a low temperature, and a short solar cycle is followed by one with a high temperature. SSH named this the Previous Solar Cycle Length Model. For simplicity, in this note I refer to it as the Solar Cycle Model or just the model. For the same reason, I usually omit the word mean when referring to the mean temperature in a solar cycle.

SSH claim that their model describes a cause-effect relationship, i.e. that it has predictive power. Solar cycle 24 had just started when they wrote their articles. SSH predicted a significant temperature decrease in solar cycle 24. That solar cycle has just ended, and now it is possible to check if their prediction came true. It did not.

The temperatures fitted well with the Solar Cycle Model until the mid-1970s, but not later. The mean temperatures during the last solar cycles have been much higher than predicted by the model.