The value of error_reporting in php.ini decides what level of error/warning repoting you want to enable. I would normally recommend that this is set to "E_ALL" for a development server and 0 for a production server. Developers should see anything that might be wrong with their code, people "out there" on the web should be denied access to this information as it would be a great help to "hackers".
So, search your php.ini for the error_reporting setting and change the line to
// Turn off all error reporting
error_reporting(0);
and watch all your warning (and error info) disappear.