Converting AppleScript Dates to UTC

on date_to_utc(list_arg)
	-- change the value of a date or a list of dates to
	-- the Universal Time Coordinated time zone
	-- Argument can be a date or a list of dates
	-- Result for a date is a date,
	-- result for a list is a list
	
	-- make sure, argument is list. Store original state
	set type_is_list to true
	if class of list_arg is not list then
		set list_arg to {list_arg}
		set type_is_list to false
	end if
	
	-- serialize arguments to plist using system events
	tell application "System Events"
		set plist to (make new property list item with properties {value:list_arg})
		set strg to text of plist
	end tell
	-- create some arbitrary date for manipulation
	copy item 1 of list_arg to date_obj
	
	-- raise error if first element of list is not convertable to date
	try
		set date_obj to date_obj as date
	on error the_error number errnum
		error the_error & " In handler date_to_utc." number errnum
	end try
	set {time of date_obj, day of date_obj, month of date_obj} to {0, 1, 1}
	
	-- find date entries in plist
	set old_delims to AppleScript's text item delimiters
	set AppleScript's text item delimiters to {"", ""}
	set temp_list to every text item of strg
	set r_list to text items 2 thru -2 of strg
	set datestrings to {}
	repeat with c from 2 to count temp_list by 2
		copy item c of temp_list to end of datestrings
	end repeat
	-- Here, we have a list of strings, representing
	-- dates in ISO notation for Zulu time zone
	-- converting the strings
	set r to {}
	set AppleScript's text item delimiters to {"-", "T", ":", "Z"}
	repeat with J from 1 to (count datestrings)
		set curr to item J of datestrings
		log "curr: " & curr
		set tl to every text item of curr
		-- result has 7 elements, the last one is empty
		log tl
		set curr to items 1 thru 6 of curr
		-- here we have a list of year, month, day, hour, minute and second as strings
		copy date_obj to ld
		-- next will set date_ob and implicitelly change strings to integers
		set {year of ld, month of ld, day of ld, hours of ld, minutes of ld, seconds of ld} to tl
		copy ld to end of r
	end repeat
	if (count r) ? (count list_arg) then
		-- this should occur only if some of the entries in the plist were
		-- of other types
		error "Some values are no dates in handler date_to_utc." number 1700
	end if
	
	-- if original argument was single, make return value single agein
	if not type_is_list then
		set r to item 1 of r
	end if
	set AppleScript's text item delimiters to old_delims
	return r
end date_to_utc

date_to_utc({current date, date ("15.5.2010 12:00:00"), date ("15.5.1975 12:00:00")})

{date "Sonntag, 8. Januar 2012 14:55:54", date "Samstag, 15. Mai 2010 10:00:00", date "Donnerstag, 15. Mai 1975 11:00:00"}