In this context: no. It's just the astronomical description (by convention) for the 180 degrees of longitude "left" of Greenwich. But sometimes I have problems with "western" designating a cultural/political unity where Australia makes part of whereas Brazil might not (depending on context).
And indeed: when, actually, is Summer 2011 in Australia?
What's wrong with "The Western Hemisphere"? The world's a sphere (roughly), so any way to denote longitudinal halves is going to be arbitrary.
Are you saying that we just shouldn't use hemispheres at all (save maybe Northern and Southern because they're not arbitrary) and instead say things like "North and South America" or "Europe, Africa, Asia, and Australia"?
I do agree that it's not a great a little awkward because the very western parts of Europe and Africa are technically in the Western hemisphere. But it is a much shorter way of denoting things than listing continents.
And indeed: when, actually, is Summer 2011 in Australia?