**  Sun Sep  9 18:04:36 2012   Andy Jacobson <andy.jacobson@noaa.gov> **

  There are many variables in these files, and you'll need to parse
  the names carefully to find what you want (hopefully it's obvious,
  if a bit tedious).  There are three sets of "regions" (reg240, tc23,
  and postagg), four classes of flux (terrestrial bio, ocean, FF,
  fire), three types of flux (imposed, prior, and optimized), and both
  fluxes and flux uncertainty are in there as well.  All the
  permutations are listed as individual variables.

  As CT2011 is a multi-model inversion, there is total uncertainty,
  within-model uncertainty, and across-model uncertainty for each
  optimized flux, and for fossil fuel emisisons.  The within-model
  uncertainty is called "internal" uncertainty, and is the average of
  each inverse model's posterior uncertainty.  The across-model
  uncertainty is called "external" uncertainty and is computed as the
  covariance across the multiple models of the posterior flux.  Total
  uncertainty is the sum of the internal and external variances.

  Geographic region definitions are in
  ftp://aftp.cmdl.noaa.gov/products/carbontracker/co2/regions.nc

  Postaggregate region definitions are in
  ftp://aftp.cmdl.noaa.gov/products/carbontracker/co2/postagg_definitions.nc.