安装 CLI（ Grunt 命令行）时出错，请帮忙看一下

按照 Grunt 官方文档安装 GLI 出错，错误信息如下：
jiang:~ bici_new$ npm install -g grunt-cli
npm ERR! Error: EACCES, mkdir '/usr/local/lib/node_modules/grunt-cli'
npm ERR!  { [Error: EACCES, mkdir '/usr/local/lib/node_modules/grunt-cli']
npm ERR!   errno: 3,
npm ERR!   code: 'EACCES',
npm ERR!   path: '/usr/local/lib/node_modules/grunt-cli',
npm ERR!   fstream_type: 'Directory',
npm ERR!   fstream_path: '/usr/local/lib/node_modules/grunt-cli',
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!      'Object.oncomplete (fs.js:108:15)' ] }
npm ERR! 
npm ERR! Please try running this command again as root/Administrator.

npm ERR! System Darwin 14.0.0
npm ERR! command "node" "/usr/local/bin/npm" "install" "-g" "grunt-cli"
npm ERR! cwd /Users/bici_new
npm ERR! node -v v0.10.35
npm ERR! npm -v 1.4.28
npm ERR! path /usr/local/lib/node_modules/grunt-cli
npm ERR! fstream_path /usr/local/lib/node_modules/grunt-cli
npm ERR! fstream_type Directory
npm ERR! fstream_class DirWriter
npm ERR! code EACCES
npm ERR! errno 3
npm ERR! stack Error: EACCES, mkdir '/usr/local/lib/node_modules/grunt-cli'
npm ERR! fstream_stack /usr/local/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:36:23
npm ERR! fstream_stack /usr/local/lib/node_modules/npm/node_modules/mkdirp/index.js:46:53
npm ERR! fstream_stack Object.oncomplete (fs.js:108:15)
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/bici_new/npm-debug.log
npm ERR! not ok code 0
请大湿指点迷津。