How can I create a view which includes all parent terms of a taxonomy term? I am creating a view which takes a tid as an argument. I then want to generate the full list of tids which includes the one directly referenced plus all those above it in its taxonomy.

How could I do this?
I guess you can't do it directly in views. You can use "Contextual filter: Taxonomy term: Term ID" and write small php code by selecting "Provide default value". 



Here is the code you can use:

$parent_terms_string = '';
$current_tid = 3; //The term ID of whose all parents you want to fetch.
$parent_terms_tid_array = array();
$parent_terms_array = taxonomy_get_parents_all($current_tid);
foreach($parent_terms_array as $term){
  if($current_tid != $term-&gt;tid){
    $parent_terms_tid_array[] = $term-&gt;tid;
  }
}
$parent_terms_string = implode('+',  $parent_terms_tid_array);
return $parent_terms_string;