CHELSA is a high resolution (30 arc sec) climate data set for the earth land surface areas currently hosted by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL (Dr. Dirk N. Karger, Prof. Dr. Niklaus Zimmermann), and has been developed in coorporation with the Department of Geography of the University of Hamburg (Prof. Dr. Jürgen Böhner, Dr. Olaf Conrad, Tobias Kawohl), the University of Zurich (Dr. Michael Kessler), and the University of Göttingen (Prof. Dr. Holger Kreft).
It includes monthly mean temperature and precipitation patterns for the time period 1979-2013.
CHELSA is based on a quasi-mechanistical statistical downscaling of the ERA interim global circulation model (http://www.ecmwf.int/en/research/climate-reanalysis/era-interim) with a GPCC bias correction (https://www.dwd.de/EN/ourservices/gpcc/gpcc.html) and is freely available  in the download section.


The data is described in this peer reviewed article:

Karger, D.N., Conrad, O., Böhner, J., Kawohl, T., Kreft, H., Soria-Auza, R.W., Zimmermann, N.E., Linder, H.P. & Kessler, M. (2017) Climatologies at high resolution for the earth’s land surface areas. Scientific Data 4, 170122.

A technical specification including the units used can be found here:

CHELSA V1.2: Technical specifications.