Re: Without human action, would the next Ice Age have started now?

Vernon,

Your question actually contains several elements, bringing together lots 
of scientific areas related to Earth's climate. You can learn a tremendous 
amount about these climate science issues through perusal of the 
realclimate.org blog, which is maintained by active climate scientists to 
provide up-to-the-minute scientific information about climate change. 
Since that site may sometimes be intimidating with the level of scientific 
details, I have "cherry-picked" some relevant points related to your 
questions. But if you want to go to the source, I would recommend you 
start with this thread http://www.realclimate.org/index.php?p=94.

1) "The astronomical truth": Surprisingly, this is the subject of active 
current research, and it doesn't look like the issues related to the 
duration of the current inter-glacial period are entirely settled. 
However, "the latest and deepest ice core from Antarctica ... seemed to 
demonstrate that ... we could probably expect another 15,000 years of 
interglacial climate even without anthropogenic forcing." This latest 
result, however, is so new that I cannot yet find a translation of it into 
non-technical language.

2) Glacial cycles vs. human climate change: "glacial" is a synonym 
for "slow," and the relevant point here is that fluctuations in the 
Earth's climate driven by orbital variations occur on a time scale much 
slower than that of the global warming we are already observing. We are 
currently observing a climate substantially changed from 100 years ago, 
and predicting even greater changes over the next century due to changes 
in the atmospheric composition caused by human activity. In contrast, the 
scientific question of glacial cycles is aimed at resolving whether the 
current interglacial period will last another 15,000 years or only perhaps 
5,000. So one answer to your questions is that at some point in the future 
it may be desirable to artificially warm the climate to avert another ice 
age, but in the near term our concern should be to reduce the impact of 
the warming we are currently experiencing.

3) The "Little Ice Age": My survey does not indicate that there is a slam-
dunk explanation of the causes of this cool period during the Middle Ages. 
It does happen to correspond to both a period of very few sunspots, and it 
also appears to correspond to a period when volcanic activity was high. 
While either of these could arguably result in a cooling of the climate, 
it doesn't look to me like anyone has proven decisively that either of 
these is the cause.

Thanks for a very good question, Vernon, and I hope your curiosity about 
our planet's climate continues!

Cheers,
Dr. Edward J. Hyer
Post-Doctoral Researcher
Naval Research Laboratory