Data files nhem_e5_xx_xxx.dat (present-day ice surface, ice base,
lithosphere surface, mask) based on

   ETOPO5. 1988. Data announcement 88-MGG-02, digital relief of
   the surface of the earth.
   NOAA, National Geophysical Data Center, Boulder, Colorado, USA.

Data file nhem80_tempmm.dat (present-day surface temperature)
based on

   European Centre for Medium-range Weather Forecast (ECMWF),
   surface temperatures for the years 1986-1989 and 1991-1994,
   personal communication (1997).

Data file nhem80_precmm.dat (present-day precipitation) based on

   Jaeger, L. 1976. Monatskarten des Niederschlags fuer die ganze Erde.
   Ber. Dtsch. Wetterdienstes 139, 38 pp.
