The study cited in the New Republic was commissioned from a group called DARA by something like 11 nations.  If you consider the New Republic less-than-credible (!) how about this article, which says basically the same thing, in Forbes?

You're really missing the point by quibbling about the secondary source. Here's the primary source, linked through the Forbes article.  Apparently, the DARA study was peer reviewed, (Although I understand that in Denierland peer review is seen as a Communist plot to take away your pickup trucks.)

http://daraint.org/climate-vulnerability-monitor/climate-vulnerability-monitor-2010/

https://www.forbes.com/sites/eco-nomics/2010/12/03/5-million-deaths-from-climate-change-pedicted-by-2020/#131e09683f42