To make historical weather reconstructions we need a large database of basic weather observations. Since the development of the barometer and thermometer in the eighteenth century, millions of people have made and recorded billions of suitable observations, and a remarkable number of these records have survived to the present day: The world's archives and libraries hold large and diverse collections of documents including weather observations. But recovering these observations is a major task: the documents with the observations are handwritten and variable in format - each page needs to be carefully read and the weather observations transcribed into computer-readable form. This task is beyond the resources of any small team of climate scientists and to achieve it will require a lot of help.
oldweather.org is a citizen science project dedicated to this task. We have started with historical records from a single source: the UK National Archive's collection of logbooks of Royal Navy ships from the period 1914-22 (our existing observational database is particularly weak in this period). These logbooks have been photographed and made accessible through the website http://oldweather.org, where a community of more than 16,000 volunteer researchers is reading and transcribing them. so far they have provided more than 1.6 million additional weather observations as well as newly detailed insights into the social and naval history of the period.