Feature Climate Year in Review: Carbon dioxide levels pass milestone Panel affirms humans’ role in warming Share this:FacebookTwitterPocketRedditPrintEmail By Erin Wayman December 23, 2013 at 4:45 pm This article is only available to Science News subscribers. Subscribers, enter your e-mail address to access our archives. Client key* E-mail* Log in Not a subscriber? Science News is a nonprofit. Support us by subscribing now. Subscribe