Data for current conditions (~1950-2000)
If you need the highest resolution (30 arc-seconds (~1 km)) then you can download by tile.
These grids (raster data) can be imported into most GIS applications.
These grids can be used in ArcMap, ArcInfo ("workstation", with the GRID module) and ArcView (with the Spatial Analyst extension).
This dataset is freely available for academic and other non-commercial use. Redistribution, or commercial use, is not allowed without prior permission.