# --------------------------------------------------------------------
# USE OF NOAA ESRL DATA
# 
# These data are made freely available to the public and the
# scientific community in the belief that their wide dissemination
# will lead to greater understanding and new scientific insights.
# The availability of these data does not constitute publication
# of the data.  NOAA relies on the ethics and integrity of the user to
# ensure that ESRL receives fair credit for their work.  If the data 
# are obtained for potential use in a publication or presentation, 
# ESRL should be informed at the outset of the nature of this work.  
# If the ESRL data are essential to the work, or if an important 
# result or conclusion depends on the ESRL data, co-authorship
# may be appropriate.  This should be discussed at an early stage in
# the work.  Manuscripts using the ESRL data should be sent to ESRL
# for review before they are submitted for publication so we can
# insure that the quality and limitations of the data are accurately
# represented.
# 
# Contact:   Pieter Tans (303 497 6678; pieter.tans@noaa.gov)
# 
# File Creation:  Tue Feb  5 13:54:57 2019
# 
# RECIPROCITY
# 
# Use of these data implies an agreement to reciprocate.
# Laboratories making similar measurements agree to make their
# own data available to the general public and to the scientific
# community in an equally complete and easily accessible form.
# Modelers are encouraged to make available to the community,
# upon request, their own tools used in the interpretation
# of the ESRL data, namely well documented model code, transport
# fields, and additional information necessary for other
# scientists to repeat the work and to run modified versions.
# Model availability includes collaborative support for new
# users of the models.
# --------------------------------------------------------------------
#  
#  
# See www.esrl.noaa.gov/gmd/ccgg/trends/ for additional details.
#  
# Data from March 1958 through April 1974 have been obtained by C. David Keeling
# of the Scripps Institution of Oceanography (SIO) and were obtained from the
# Scripps website (scrippsco2.ucsd.edu).
#
# The "average" column contains the monthly mean CO2 mole fraction determined
# from daily averages.  The mole fraction of CO2, expressed as parts per million
# (ppm) is the number of molecules of CO2 in every one million molecules of dried
# air (water vapor removed).  If there are missing days concentrated either early
# or late in the month, the monthly mean is corrected to the middle of the month
# using the average seasonal cycle.  Missing months are denoted by -99.99.
# The "interpolated" column includes average values from the preceding column
# and interpolated values where data are missing.  Interpolated values are
# computed in two steps.  First, we compute for each month the average seasonal
# cycle in a 7-year window around each monthly value.  In this way the seasonal
# cycle is allowed to change slowly over time.  We then determine the "trend"
# value for each month by removing the seasonal cycle; this result is shown in
# the "trend" column.  Trend values are linearly interpolated for missing months.
# The interpolated monthly mean is then the sum of the average seasonal cycle
# value and the trend value for the missing month.
#
# NOTE: In general, the data presented for the last year are subject to change, 
# depending on recalibration of the reference gas mixtures used, and other quality
# control procedures. Occasionally, earlier years may also be changed for the same
# reasons.  Usually these changes are minor.
#
# CO2 expressed as a mole fraction in dry air, micromol/mol, abbreviated as ppm
#
#  (-99.99 missing data;  -1 no data for #daily means in month)