Yesterday, the US Library of Congress announced a change to its social media archiving policy. In 2010, the LOC had been given a complete archive of every tweet sent to that point; it has been grabbing every single new one since. But starting on the first of January, the archiving will become selective; only tweets that are deemed newsworthy will be kept.

The LOC describes the decision in a very short white paper. Part of the reasoning is the sheer volume of data; the number of tweets is up, and their possible length has been doubled recently. But it's also a matter of being able to actually preserve content. Tweets now embed pictures, videos, and previews of the content of any links they contain. The LOC has been preserving only text and, therefore, is missing out on an increasingly important portion of the information content of any tweet.

In addition, the Library's normal role is as a curator, preserving information that's thought to be most significant or valuable. In this sense, the change will bring its Twitter policy more in line with its general approach to collecting.

That doesn't mean the librarians think that the preservation of every tweet for more than a decade wasn't valuable. It notes that the collection captures a period where social media has played an increasingly important role in public discourse and private lives and when Twitter rose from obscurity to be a place where significant statements are placed in the public record. Having all tweets also captures the response of average people to historic events; the white paper points to the collection of recordings of interviews made in the aftermath of the Pearl Harbor attack as being similarly valuable.

Future decisions on which tweets to preserve will be made using guidelines for general collecting that apply to other areas. In the meantime, the LOC still hasn't decided how best to provide the public with access to all the tweets it currently has. So if you want to dig into history to find a case of a politician's past statements criticizing their present actions, your best bet remains using Twitter's own search features.