"Pete L" wrote in message
...
I am a retired meteorologist - just an interest in astronomy. The last
ice age ended about 20k years ago. Nobody really knows why ice ages
happen but I have often wondered about interstellar dust. Seems
reasonable to me that as the solar system rotates around the galaxy it
may encounter dust clouds which would reduce solar radiation reaching
the Earth and thus trigger ice ages. There are some suggestions that
the sun is a variable star. How would it be shown if this could just
be due to interstellar dust? Would this dust actually be between the
Earth and the Sun or would the solar 'wind' keep it away?

The current ice age did not end 20 k years ago. With ice at both poles we
are
still in it! What did occur 20 ka was the last glacial maximum, and we are
now in an interglacial. The previous interglacial (the Eemian) happened
about 100 k years ago and lasted about 10 k years. The current interglacial
(the Holocene) has lasted about 10 k years so far.

The cause of glacials and interglacials is known. It is related to the
Earth's orbit around the Sun by a mechanism known as Milankovitch cycles.
These cycles have periods of roughly 21 k, 41 k and 100 k years. The overall
cycle consists of a 80 k cooling, 10 k warming and 10 k interglacial. During
the rapid warming CO2 concentration increases and it is believed that it
acts as a positive feedback.

The ice ages (the first of which goes back to 2,000 M years ago,) seems to
have been be caused by episodic drawdowns of carbon dioxide from the
atmosphere as life evolved in a world where the Sun has grown steadily
stronger, but there is still doubt about the causes of each of those.

Dust from volcanoes, when injected into the stratosphere, does cause cooling
e.g. Tambora in 1815 caused 1816 to be the year without a summer, but
interstellar dust would not be dense enough to have had such an effect.

Cheers, Alastair.