nodo npm Installazione di bower = npm ERR

Nuovo computer, nuovo inizio. Stava installando bower dal terminale e ottenuto questo ERR! messaggio in cambio. Sembra comune, ma sono titubante nel forzarlo con sudo.

• OSX 10.10.3
• git versione 2.3.2 (Apple Git-55)
• npm (2.9.1)
• node v0.12.3 sono installati.

npm install -g bower

npm ERR! tar.unpack untar error /Users/username/.npm/bower/1.4.1/package.tgz
npm ERR! Darwin 14.3.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "bower"
npm ERR! node v0.12.3
npm ERR! npm  v2.9.1
npm ERR! path /usr/local/lib/node_modules/bower
npm ERR! code EACCES
npm ERR! errno -13

npm ERR! Error: EACCES, mkdir '/usr/local/lib/node_modules/bower'
npm ERR!     at Error (native)
npm ERR!  { [Error: EACCES, mkdir '/usr/local/lib/node_modules/bower']
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   path: '/usr/local/lib/node_modules/bower',
npm ERR!   fstream_type: 'Directory',
npm ERR!   fstream_path: '/usr/local/lib/node_modules/bower',
npm ERR!   fstream_class: 'DirWriter',
npm ERR!   fstream_stack: 
npm ERR!    [ '/usr/local/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:36:23',
npm ERR!      '/usr/local/lib/node_modules/npm/node_modules/mkdirp/index.js:46:53',
npm ERR!      'FSReqWrap.oncomplete (fs.js:95:15)' ] }
npm ERR! 
npm ERR! Please try running this command again as root/Administrator.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/username/npm-debug.log