[Eda Meltzer]

Eda Meltzer  asked the Naked Scientists:
   
Please can you tell me why the ice melted at the end of the ice age?
 
There was no man-made global warming then, so what was the reason?

What do you think?

[SteveFish]

The ice ages originate from Malankovitch cycles that involve regular variations in the earths orbit and axial tilt relative to the sun. When several values occur at the same time the temperature of the northern hemisphere is shifted slightly in a warmer or colder direction. A number of factors that affect climate will amplify the small change, just like for human generated warming. For example, when it is a little warmer in the northern hemisphere (where most of the land mass is) the snow will recede at the end of winter a little faster. Snow reflects light and keeps the earth colder, so a little less snow allows the earth to warm up more. This is called a change in the earths albedo (reflectivity), and water vapor and greenhouse gasses are also positive feedbacks. I think that the main cycle time is around 100,000 years, but there are various shorter and longer cycles as well that aren't as strong.

[CliffordK]

You mean it wasn't people driving SUVs?

There are numerous theories.  Some notes discuss the changes of sea flow through the Bering Strait, although one might have to ask what the cause for the ice blockage to disappear.

I saw one article about changes of solar radiation from the sun.

[SteveFish]

Clifford:

I am curious as to what specific changes in solar radiation have been suggested to be involved in the ice ages, or with the current interglacial. The Malankovitch cycles affect how much solar radiation specific regions receive, but I assume you are talking about changes in the sun itself. Also, have you found a theory that suggests that ocean circulation, specifically through the Bering Strait, is a key factor for all the interglacials, for the most recent one, or just a component.

Steve

[CliffordK]

There is a lot of information on the web about sunspots, sunspot cycles, and magnetic states within the sun.  The sunspots, while they are cooler in the spot, they are actually an indicator of more solar activity.

There is a lot of information about decade (11 yr) long sunspot cycles.

http://earthobservatory.nasa.gov/Features/SORCE/sorce_03.php

However, there are also notes about even longer cycles. 

http://sc25.com/index.php?id=44
http://www.examiner.com/weather-in-atlanta/sun-spot-cycle-impacting-global-warming-and-cooling

Evidence of 6 000-Year Periodicity in Reconstructed Sunspot Numbers
http://www.springerlink.com/content/v856256j65142l48/fulltext.pdf

See Wikipedia:
http://en.wikipedia.org/wiki/Solar_cycle

Recorded sunspots for the last 400 years.


I think there is an effort to use Carbon-14 to make longer term records of sunspots and solar irradiation cycles.

Predictions of the "Next Ice Age".
http://sc25.com/index.php?id=44

There have also been notes of global warming on Mars, although a lot of criticism of those indicate the longer Martian year perhaps having a confounding effect.  Likewise, there are reports of warming on one of the moons around Neptune, Triton.  Perhaps also Jupiter's moons.

http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html
http://www.livescience.com/environment/070312_solarsys_warming.html

Here is also a note about observed changes in irradiation from Alpha Centauri-A
http://www.livescience.com/environment/070312_solarsys_warming.html

Anyway, there was another article that discussed mathematical/computer simulations about shifts in the magnetic configuration in the sun.  But, I seem to have misplaced it at the moment   []

Everything indicates very complex interactions of solar irradiation & sunspots, volcanic activity, perhaps asteroid impacts, Plants, Carbon Dioxide, CO₂ "Weathering", Carbon and Carbon Dioxide becoming trapped in the oceans and other sinks, ocean flow patterns, etc.

Right now we're just barely scratching the surface with long-term climate predictions.

[SteveFish]

Clifford:

Actually climate science is a pretty mature field that can explain quite a lot about how the physics of the atmosphere works. I have been reading quite a bit about this lately from the actual scientists who collect data and publish. I looked at all of your links and you only need to read two, the article on the NASA website and the Wikipedia article. Total solar irradiance is ~1368 W/M² and the total swing in this from sunspot cycles, and variability from none to many sunspots, is 1.4 W/M². This obviously does affect climate but is not enough to make much difference in temperature, much less start or stop an ice age. There are a couple of periods when other factors combined with sunspot minimums to make a noticeable difference, but usually not much more than one degree cooler.

I was surprised to see two links to two articles by Timo Niroma. He is not a scientist and doesn’t do any actually research on the topics he comments on. He is a known anti science writer of opinion pieces that are often published in Energy and Environment which is not peer reviewed or even listed in the ISI index. He likes to make extravagant claims that he can’t back up.

The Live Science article was OK but had little information, just opinions. There was nothing in it on Alpha Centauri that I could see. In fact, all the hype about warming on other solar system planets and moons are incorrect distortions of good research. For example, the research paper that identified warming on Mars found it to be due to weather and changes in the amount of dust in the atmosphere. The warming study on Jupiter was actually a prediction from an atmospheric climate model that had been modified to fit Jupiter. The warming was never actually measured just predicted.

The rest of the articles were just opinion pieces which contained no, or very few citations of actual research, and there was nothing at all about factors that are a causative factor for ice ages or interglacials except for a mention of Malankovitch cycles in the Live Science piece. Perhaps you should read up on this.

Steve