$carbon = new CarbonCarbon($dateasstring);
$local = $carbon->timezone($localTimeZone);

// example from artisan tinker:
[1] > $utc = new CarbonCarbon('2014-01-05 12:00:00');
// object(CarbonCarbon)(
//   'date' => '2014-01-05 12:00:00',
//   'timezone_type' => 3,
//   'timezone' => 'UTC'
// )
[2] > $warsaw = $utc->timezone('Europe/Warsaw');
// object(CarbonCarbon)(
//   'date' => '2014-01-05 13:00:00',
//   'timezone_type' => 3,
//   'timezone' => 'Europe/Warsaw'
// )

private function totimezone($utc){
    $usertz = Session::get('timezone');
    $carbon = new Carbon($utc, 'UTC');
    $carbon->timezone = new DateTimeZone($usertz);
    return $carbon;

}

private function toutc($local){
    $usertz = Session::get('timezone');
    $carbon = new Carbon($local, $usertz);
    $carbon->timezone = new DateTimeZone('UTC');
    return $carbon;
}