A friendly discussion about the inlfuence of the sun on climate....
After the most recent thread about MMGW got closed, I'd like to start a friendly and sensible discussion about the impact of the sun on the earth's temperature.From what I've read, there is little to suggest that the huge ranges of temperature that the earth has experienced in its very long existence correlate well with levels of CO2 but do show some correlation with solar activity.
The questions I'm therefore looking for a response to are:
1) How much do you believe that solar activity influenced the climate historically?
2) What caused the Medieval warm period and Maunder / Dalton minima?
3) What caused the earth to heat up to take us out of the last ice age?
Friendly, evidence-based comments only, please!
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Sidicks Err the Sun.
Following your posts in the other thread, I went and looked for data on Solar output - couldn't find anything (in an admittedly brief search) to support the hypothesis that we're heading for a new Maunder minima.
Do you have links that support that idea ? May I point out nice and early in the thread that if anyone finds it impossible to debate the issues without getting personal or arrogant, it's likely to be the last post that they make on AV Forums The suns influence on climate is, of course, extremely long-term. In historical times it has had far greater influence on the weather. The mediæval warm period was a weather event, probably caused by climatic and solar cycles coming together in a rare conjunction. It is not precisely understood.
There are several possibilities as to why ice ages come and go. The cooling effects are reasonably well understood. Random events come together to create an unusually long cool period. This removes CO2 and other gases from the atmosphere (primarily CO2), and the greenhouse effect is reduced. Floating ice sheets penetrate the lower latitudes, and they reflect sunlight. The result is a positive feedback cooling loop.
Emergence from an ice age comes from random warming events releasing CO2 to increase greenhouse warming. There are several possible causes, and probably all have played their part in the past, but the most probable is volcanic activity. This has two effects: it releases vast amounts of CO2, and if it occurs at high latitudes melts the ice and deposits large amounts of dark coloured ash onto reflective surfaces.
Mods: Do you agree that we should try not to allow this thread to degrade into a MMGW debate by the back door, as I suspect may have been intended? All questions relating to solar activity and their relevance to MMGW were answered, courteously and in some detail, in the recently-defunct thread, which is still open to readers. Why would the sun's influence have been much more significant in the past than the present or the future?
I thought there was some evidence that the medieval warm period lasted a long time and was not isolated in a single region, which would surely suggest it was more 'climate' than 'weather'?
I will do some more research.
Random events seem a bit 'vague'.
Again, much is being made of 'random' factors which suggest the factors which influence the climate are not well understood.
No need to pre-judge what was intended.The last thread degenerated due to certain individuals preferring to hurl insults rather than discuss the issues!
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Can you point me to the thread you refer to?
Thanks
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Sidicks Well, yes and no. We know what the factors are. They include:
Solar activity;Biological activity;Atmospheric greenhouse gases (including CO2, water, methane), from whatever source;Volcanic activity;Meteoritic impact;Variations in the Earth's magnetic field;There are probably others, but I can't think of them off-hand.
Note that some of these are not independent or random; greenhouse gases especially are largely a result of the others - see below. Whilst all events have a cause and thus aren't really random, for the purposes of this discussion most of them can be considered as such.
We don't know how they interact in any given combination to cause climate shift (or create a climate, if you will). We do know that they can be considered prime causes. Their major impact on climate, though, is through their common secondary cause, which is greenhouse warming/cooling. We also know that their combinatory effect is chaotic and highly non-linear, which is one of the reasons climate modelling is proving so intractable. The sun is a variable star after all. Its vagaries and natural cycles drive everything. By stellar standards the Sun is a very stable star. Its output doesn't vary by more than 0.1% over millennia. Float us around a variable star, and we'd know about it, believe me. For the few weeks or months we'd survive.
I'm not sure what you mean by 'everything'. Its cycles have very little impact on the biosphere, but probably influence weather systems to some extent. They help to sustain climates, but have little impact upon climate change because they are highly regular and don't vary over time. Absolutely right. The only thing that has been left out is the solar activity cycle. From maximum to minimum activity is about 11 years.
For the sun's variability to have a tangible impact on climate change, we would expect to see 11 year cycles in the climate wouldn't we? That is the short term cycle - there appears to be a longer term cycle as well, which caused the Maunder Minima etc
Chilly Temperatures During the Maunder Minimum : Image of the Day
We probably do - but the variability (over the 11 years) is too small, and just becomes part of the statistical noise.