Ok closet Physists and Chemists… here’s a Question for y’all… Does anyone know, if it’s reasonably possible that the Sun could change temperature enough, that it could be felt, on a measurable scale here on Earth. Meaning, could the Sun say, cool off a bit, making the average temperature drop a few degrees. Depending on the responces, I’ll give a detailed story behind the Question.
Thanx!
There is some suggestion that small-scale solar variability contributes to climate change, but it’s hard to determine precisely to what extent with the data we have in hand. A few degrees change in the global average temperature might not be out of the question, but that will depend on the responses of other climate feedbacks as well.
So, what’s the detailed story?
Over geological times the sun is warming as more and more helium “ash” accumulates. Basically the sun “burns” hotter when it fuses helium. I think 2 billion years ago it was 75% as bright as it is now. I’ll dig for a site, but I’m guessing you want a shorter term solution right?
The estimates of original solar luminosity vary depending on the model of stellar evolution that you favor, but the sun is thought to have been 25-30% less luminous at the time the Earth formed 4.56 billion years ago. By 600 million years ago, it was somewhere between 4 and 6% less luminous than the modern value.
I also think the OP was thinking of something much more recent though, in which case the luminosity fluctuations are on the order of tenths of a percent deviation from modern.
In billions of years, when the sun runs out of fuel, it will become a red giant engulfing the inner planets including the earth. I imagine that could include, amoung other things, a tempurature change felt on the earth.
Ok, I had come up w/ the idea that maybe Ice Ages may have been caused by variences in the energy output of the Sun, as opposed to prevailing theories such as metorites and/or Dinosaur farts. I thought this to be a rather novel idea and one that would be virtually impossible to prove since we can’t record changes in the Sun on enough of a long time scale to prove one way or another. Plus, I know of no way to measure it geologically, as sun radiation probably doesn’t leave much in the way of geological evidence.
I proposed this idea to a buddy of mine, and as usual, he said I was full of poop. And went on to say it was IMPOSSIBLE for the sun to have ANY variances to it. Because if there were, it would be ‘unstable’ and immediately collapse (or explode I guess). While he has more college than I do, he’s not a scientist or even a physics (or would this be chemestry) major. So I take his opinion w/ a grain of salt. However, he got quite pissed off (as he usually does) that I didn’t accept HIS theory outright and we argued over this non-sence for several hours.
Anyway, so as some of the links have proposed, I am not the ONLY one to have thought of this idea, which is comforting to know ;o) … So, if anyone knows of any further links, specifically to the idea of the Sun being the cause of Ice Ages, I’d appreciate any input.
Thanx!
Since at the time mentioned the sun will expand and engulf the earth, there is no doubt that there will be an increase in temperature on the earth. 
The concentration of oxygen-18 (an isotope) in coral carbonates varies with solar output. Here’s a bit on Paleoclimatology.
The sun will increase it’s (and thereby our) temperature enough in a billion or so years I believe so that it is possible a very strong greenhouse effect could take place, extinguishing life. The expansion of the sun into a red giant will occur in another 4.5-5 billion years or so, and it will grow to past our current orbit, but it’s gravity will not be as strong and we will be about 1.5 AUs out instead of our current 1 AU from the sun.
I’m a former physics/astrophysics major, and I say your friend is full of poop.
It is easily possible for a star to vary strongly in luminosity, and to do so for ages. Cepheid variables do it all the time, for pretty much their entire lives. For that matter, it is easily possible for most any physical system to be oscillatory in some attribute. All you need is a state of stable equilibrium plus a driving force.
Of course our sun is not such a variable star. That’s just my example of how variance in a system does not lead automatically to self-destruction. The sun’s luminosity does have minor luminosity fluctuations, though they’re not big enough to “feel”. (I certainly can’t feel them.) Moreover, I had understood the Ice Ages are believed to be a chaotic effect of earth’s climate, not one driven by the sun. (One article I’ve read in Scientific American suggests that the earth might actually spend a majority of its time in ice ages. We just happen to be living right now between the last one and the next one.)
Ultimately, you could say the sun is unstable, in the sense that it won’t last forever. In five billion years, the hydrostatic equilibrium it has enjoyed all this time will fail, when it expands to engulf us all, then collapse to a white dwarf.
While there are occasionally hyotheses floated that the gravitational constant might vary with time, there is thus far no evidence whatsoever of it. And the Sun’s mass isn’t appreciably changing, either, so the gravity of the Sun on the Earth will be just as strong then as it is now.
And Cepheids do not vary for “pretty much their entire lives”, unless you mean their entire life as a Cepheid. A Cepheid is in a fairly advanced stage of stellar evolution, after having spent most of its life on the Main Sequence. In fact, the timescales involved are short enough that we have been able to watch some stars evolve into or out of the instability strip (the portion of the HR diagram which includes Cepheids and RR Lyrae variables): Polaris is one such example, having recently been a Cepheid, but not any more.