Further details can be found here.
For anyone wondering how they can help to improve the data holdings right now, you might want to take a look at either http://www.data-rescue-at-home.org/ for upper air and land surface records, or http://www.oldweather.org/ for world war 1 UK ship records. It is hoped that many of the substantial land data holdings currently available only in image / hard copy form can eventually be digitized by citizen scientists over the internet.
Moderated blog for issues relating to work on surface temperature records as part of an international effort.
