Automatically increase comment karma on comment save

The comment_karma field in the wp_comments table is something that has been in present in WordPress for a long time, but never utilized by the WordPress core itself.

You can update it the same way any other comment field is updated, using update_comment():

$comment_data = array();
$comment_data['comment_ID'] = 1;
$comment_data['comment_karma'] = 123;
wp_update_comment( $comment_data );