So what’s all this about sunspots then? How do they affect the Suns influence on our climate?
When I was a geeky teenager, nearly 40 years ago and before global warming was heard of, I read of the ‘Maunder Minimum’, a period in our history when there were almost no sunspots. During these years our weather was much colder than usual with rivers such as the Thames freezing over in winter. The ice was so thick that people held ‘frost fairs’ on it!
Yet, since we have been able to measure the Suns output directly, it has not varied by more than 0.1%. Surely this means that, at least in the normal solar cycle, sunspots are irrelevant. Doesn’t it?
Many on here say that there is no man made global warming, that changes in the Sun are responsible and cite the current low sunspot activity as evidence of recent cooling.
Clearly, this cannot be true since solar output is virtually constant, (see above)…
…so what did happen during the Maunder Minimum?
Is there another explanation? Was the lack of sunspots a coincidence?… or a symptom of some change in the Sun.
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I believe global warming is happening and that, since the industrial revolution, we are the main cause.
But I do find the question of variations in the Sun an interesting one.
If you can shed any light on this, especially the significance of sunspots, please do…
Evans michael ya, I’m afraid you are wrong on TSI.
Total Solar irradience does not just mean visible light, it means the whole electromagnetic spectrum.
Anyway, from reading your links, this is my understanding of the effect of solar variation on climate.
The theory is that cosmic rays (among other causes) seed clouds, which reflect a percentage of sunlight back into space, thereby having cooling effect on the planet. If the number of cosmic rays changes, cloud formation is affected, also the amount of cooling.
Changes in solar output (TSI), linked to sunspot numbers, cause changes in the strength of the solar wind, which changes the amount of cosmic rays from deep space that are hitting the Earth. The evidence for this is in the varying amounts of cosmic ray induced, Beryllium 10 isotopes produced and trapped in ice cores, which corresponds well with sunspot numbers recorded since 1610.
There is speculation that, during periods such as the Maunder Minimum, the Sun shows greater variation than the 0.1% as recorded by satellite observations, a figure of 0.5% to 0.8% being suggested. Given that the MM did occur, and was pre industrial, this seems to be a reasonable possibility, though at the moment there is no evidence to support this.
Astronomers are making observations of ‘sun like’ stars in an attempt to test this idea. So far, observations of the first ‘near identical’ star found, 18 Scorpii, suggest that the present behaviour of the Sun is completely normal! To date, a total of 5 ‘solar twins’ have been found, some of which may be in ‘Maunder Minimum’ phases. Observations are ongoing and will probably lead to a much better understanding of solar changes in the next few years.
http://www.astrobiology.com/news/viewpr.html?pid=21892
Where the theory seems to run into difficulty is in the idea that cosmic rays are linked to cloud formation. I’ve had a quick search and there seems to be more against the idea than in support of it.
But even if it was true, can it explain the warming we have seen in recent decades?
From evans michael ya‘s 1st link, (the Lowell Observatory blog).
‘Our understanding of the role of solar variations in climate change is based largely upon observations of the Sun’s total brightness variability. As those of you who follow these things know, the 0.1% variation in solar brightness over the course of its activity cycle does not impart sufficient radiative forcing to account for climate change since about the mid 20th century; another, presumably anthropogenic, signal must be present.
…and from a link on that blog, (the solar stellar spectrograph).
‘In studying solar influences on climate, therefore, I am not interested in making Texaco happy, and I am not interested in making Al Gore happy. I’ll publish whatever the data tell me, and my recent stellar observations suggest that from an astronomical standpoint at least, Al (Gore) is correct in pointing the finger at human activities as an increasingly important component of climate change.’
Finally, here is the sunspot history since 1870…
http://www.uma.pt/Investigacao/Astro/Grupo/Sextas_astronomicas/Sexta14/144051main_ButterflyDiagramLG.jpg
I’m sure you will agree, solar activity has been steady for at least 70 years. If the Sun was the main, or only, influence on our climate, there would have been no warming over this period, cosmic rays or not!
…and a graph that speaks for itself!
http://solar-center.stanford.edu/sun-on-earth/600px-Temp-sunspot-co2.svg.png
After much thought, I am going to give best answer to evans_michael_ya, mainly for the link to the Lowell observatory. I got much from this link, also the links it lead to.
Having said that, I could not find anything to back up the idea that ultraviolet variability is much larger than the total variability. To be honest, this sounds rather contrived and, in the absense of evidence, I just don’t believe it!
I think Dana’81 has summed up the situation correctly as regards present and historical warming. What ever happened during the Maunder Minimum was natural but natural processes are unable to account for what is happening today.
Another good answer; the soup and darkness from Linlyons.
Thank you both and thanks to everyone else for your answers.
If anyone can provide more evidence for the cosmic ray or ultraviolet variability theories, please do this via the comments.
…or is there no evidence apart from the need to oppose the idea of man made global warming?
Actually, that .1% variation is just variation in visible light (TSI). Here’s a link discussing the flaw with using TSI to dismiss the sun’s role in climate change:
http://www.lowell.edu/blog/?p=89
"In an opening keynote talk, Judith Lean of NRL reviewed the status of solar irradiance variability models relative to the latest observations of the total solar irradiance (TSI) as measured by SORCE. Judith made a number of points, but to my mind, here’s the central one. Our understanding of the role of solar variations in climate change is based largely upon observations of the Sun’s total brightness variability. As those of you who follow these things know, the 0.1% variation in solar brightness over the course of its activity cycle does not impart sufficient radiative forcing to account for climate change since about the mid 20th century; another, presumably anthropogenic, signal must be present. Here’s the critical twist: the spectral distribution of the Sun’s cyclic variability is quite different depending on where you look in the spectrum. In particular, the ultraviolet variability is much, much larger than the total variability — a few tens of percent — and the UV radiation significantly affects the stratosphere, in ways that are poorly understood. The next avenue for real progress in Sun-climate relationships lies in breaking down the total irradiance variation into its spectral components, and beginning to understand what effects they have on climate. We are just now starting to assemble the observations, which must be done from space, to address this issue."
Evidence solar UV radiation variability and coronal holes are affecting Earth’s atmosphere found here:
http://www.sciencedaily.com/releases/2008/12/081215184317.htm
"While extreme ultraviolet radiation from the sun is the dominant mechanism that causes the thermosphere to "breathe," the new CU-Boulder study indicates high-speed wind from the sun triggers independent breathing episodes by creating geomagnetic disturbances, heating the thermosphere and altering its density. The wind streams are generated by relatively cool pockets on the sun’s surface known as solar coronal holes that periodically rotate around the sun’s surface, said Thayer.
"We were surprised to find the density changes were so consistent in our observations," said Thayer, lead study author. "Because of the huge increase in satellite activity in recent years, finding this new thermosphere breathing mechanism should help improve our models and increase the accuracy satellite tracking and collision avoidance.""
We are currently at a solar minimum between solar cycles 23 and 24…one of the quietest seen in several cycles. Just as you were taught about the ‘Maunder Minimum’, we are currently living in ‘The Modern Maximum’: The most active period of solar activity seen in over a thousand years. The current silence from ol’ Sol suggest this period of extreme solar activity may be waning. If so, expect cooler than average temps to prevail over the next few decades.
"Claus finds that right now, near the dead minimum between solar cycle 23 and 24, the Sun is fainter than it was between the 1996 minimum of cycles 22 and 23. This is hugely important, since identifying changes in the solar brightness at minimum, when the Sun is mostly or entirely free of “active” features like sunspots, is perhaps the critical observation for determining whether the Sun is growing steadily brighter or fainter on the long term. Even more interesting, my preliminary analysis of my 2007 spectroscopic observations of the Sun show the same thing…it looks like the current minimum is lower than the last one." -same link as first
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