How can I ignore committing timezone information in my commit?

Recently, I forked a repository hosted by github, with contributors spreading all over the world, and found out that the each commit log contains committer's timezone information.

2013-11-07 02:31:41 +0545 <-- This committer is living in Nepal. Surely.
2013-11-04 12:58:36 -0600 <-- This committer is living in CST or Ecuador or Chili or ...
2013-10-31 10:36:36 +0700 <-- This committer is living in Indonesia or Thai or Mongolia or Laos or Australia or ...
:

I know it's possible to hide this by editing the output form (e.g. git: timezone and timestamp format), but this hides what's actually saved in github's repository, only from my eye. Each committer's timezone is surely saved in github's server.

So my questions:

1. Why are committer's timezone needed for commits? What is it used for? Isn't UTC time enough?
2. Are there any options to ignore MY computer's timezone setting when committing? I don't want to set my computer's timezone to UTC, only because git is implicitly committing it.

You can use this command to commit in UTC time:

git commit --date="`date --utc +%Y-%m-%dT%H:%M:%S%z`"

You can also alias it to a convenient name:

git config --global alias.commitutc '!git commit --date="$(date --utc +%Y-%m-%dT%H:%M:%S%z)"'

And do git commitutc.

For a more detailed explanation take a look at this blog post.