On Mon, Oct 19, 2015 at 4:51 PM, Rob O'Connor <xxxxxx@ozemail.com.au>
wrote:
> For the sake of rough quantification, using Earthly examples:
> Last glacial maximum/ice age equals depressing average surface temperature
> by 5 Kelvin
> Nuclear winter, 5-10 Kelvin
> Freezing all life, more than 30 Kelvin

Mean surface absolute temperatures go roughly with the fourth root of
irradiance.  Halving the irradiance would drop the mean surface
temperature by approximately 16%, which corresponds to about 45 K
reduction.  That would easily be enough to eventually turn Earth into
an iceball with no liquid surface water.  Some deep subterranean
and/or extremophile bacteria might survive.

> Bigger hotter stars will be harder to block.

Actually hotter stars would be easier to block, since a planet of
given starting temperature would be further away with a lesser angular
diameter of star.

- Tim