By Frank Bosse and Prof. Fritz Vahrenholt
(Translated/edited by P. Gosselin)
Our source of energy continued to be especially quiet last month. The mean sunspot number (SSN) was 17.7 and the sun was completely blank for 16 days.
It is important to recall once again that the SSN is not simply the sum of the observed sunspots, rather it is generated by the number of spots multiplied by the 10-fold of the observed sunspot regions. When one single spot is observed in an active region, this yields an SSN of 11.
The mean SSN for all cycles recorded so far, up to month 100 into the cycle, is 48.6, which means that the current cycle has seen a solar activity that is only 36% of the mean. It’s a weak cycle.
Fig. 1: The current solar cycle (SC) 24 is shown in red and is compared to the mean of the previous 23 cycles (blue) and the similar SC 5 (black).
What follows is a comparison of all cycles observed thus far:
Fig. 2: The accumulated sunspot anomaly between each cycle and the mean (depicted in blue in Figure 1).
As the chart above shows, the current cycle is the 3rd quietest overall since observations began in the 17th century. Overall only SC 5 and 6 (Dalton-Minimum) were quieter (so far). What is especially remarkable is that the 75 – 100 month period of the current cycle is the quietest of the such ever.
A real drop off in activity
Compared to the 1930 – 2000 period, the current cycle in fact represents a real drop off in activity. If we smooth the curve over 4 cycles, this is what activity looks like since systematic sunspot observations began:
Fig. 3: 44-year smoothed sunspot curve using Loess filter 44 SIDC (orange) and the mean value since 1700 (brown). In amplitude and time period, the 1930-2000 years were the most active of the past 300 years. The current drop-off has a strong similarity to that seen during the Dalton period.
We are of course keeping an eye on the solar polar fields. At this point into the cycle, its strength is an indicator of the activity may be in the upcoming SC 25. Since December not much has changed, and so we will continue to stick to our prognoses from last month: The coming cycle will be approximately 1/3 weaker than the current SC 24.
The next few billion years
Over large timescales, the sun’s thermonuclear furnace strengthens at its core as the sun ages. The “solar constant” is currently ca. 1362 W/m², but is in fact not constant because it is increasing. There are a number of publications about this, and one recent study has come to the following result: Over the next 1.3 billion or so years, it is gradually going to get warmer as the sun will gain about 12% more strength compared to today. For the climate system that will result in about 41 W/m² in effective greater forcing (compared that to about 3.8 W/m² for a doubling of CO2, according to scientific literature). This will lead to a new modus for the earth’s climate, as temperatures will rise about 20°C. Naturally this is nothing to worry about, as by then we’ll be long gone.
That of course will not mean the end of life on earth as water will continue to exist and the earth will stabilize at its new plateau. And as the sun gains another 10% in strength, water will rapidly be lost into space. That will be the case in about 2.1 billion years. Later after that life as we know it will cease to exist on earth. And another 4 billion years later the sun will engulf the parched earth as it expands into a red giant.
But as far as we are concerned today, there is no need for pessimism! And don’t forget: there will continue to be an ice age every 100,000 or so years – just as this has been the case over the recent geological past (2 million years). And even if man should succeed in doubling the atmospheric CO2 concentration, the earth will not turn into Venus. For that an additional forcing of 72W/m² would be necessary.