jquery - use a variable outside the function

How I Can use a variable outside the function where it was declared?

$(function() {
    function init() {
        var bwr_w = $(window).width();
    }
    init();
    $('#button').click(function() {
        alert('The Browser Height is' + bwr_w);
    });
});

If I click on the button I get this error:

bwr_w is not defined