! source file: /Users/nmengis/Documents/UVic_ESCM/2.10.backup/updates/02_CE_permafrost_merge_CMIP6forcing/source/common/aggdata.F
       subroutine aggdata

!=======================================================================
!     routine to read and interpolate additional greenhouse gas forcing
!     data
!=======================================================================

      implicit none

      character(120) :: fname, name, new_file_name, text

      integer iou, n, ln, ib(10), ic(10)

      logical inqvardef, exists

      real dat(3), data_time, tim(3), wt1, wt3, c1e3

      real, allocatable :: data(:), time(:)

      save dat, data, ln, tim, time

      include "size.h"
      include "param.h"
      include "pconst.h"
      include "stdunits.h"
      include "calendar.h"
      include "cembm.h"
      include "switch.h"
      include "tmngr.h"

      c1e3 = 1000.

      if (.not. allocated (time)) then
        name = "A_aggfor.nc"
        fname = new_file_name (name)
        inquire (file=trim(fname), exist=exists)
        if (.not. exists) then
          print*, "==> Warning: ", trim(fname), " does not exist."
          ln = 3
          allocate ( time(ln) )
          allocate ( data(ln) )
          time(:) = year0
          data(:) = 0.
        else
          call openfile (fname, iou)
          call getdimlen ('time', iou, ln)
          allocate ( time(ln) )
          allocate ( data(ln) )
          ib(:) = 1
          ic(:) = ln
          call getvara ('time', iou, ln, ib, ic, time, c1, c0)
          text = 'years'
          call getatttext (iou, 'time', 'units', text)
          if (trim(text) .eq. "days since 1-1-1")
     &      time(:) = time(:)/yrlen - 1.
          if (trim(text) .eq. "days since 0-1-1")
     &       time(:) = time(:)/yrlen
          if (trim(text) .eq. "years since 1-1-1")
     &      time(:) = time(:) - 1.
          exists = inqvardef('A_aggfor', iou)
          if (.not. exists) then
            print*, "==>  Warning: A_aggfor data does not exist."
          else
            call getvara ('A_aggfor', iou, ln, ib, ic, data, c1e3, c0)
          endif
        endif
        tim(:) = time(1)
        dat(:) = data(1)
      endif

      tim(2) = min(time(ln), max(time(1), aggfor_yr))

      if (tim(2) .le. time(1)) then
        dat(2) = data(1)
      elseif (tim(2) .ge. time(ln)) then
        dat(2) = data(ln)
      else
        if (tim(2) .gt. tim(3)) then
          do n=2,ln
            if (time(n-1) .le. tim(2) .and. time(n) .ge. tim(2)) then
              tim(1) = time(n-1)
              dat(1) = data(n-1)
              tim(3) = time(n)
              dat(3) = data(n)
            endif
          enddo
        endif
        wt1 = 1.
        if (tim(3) .ne. tim(1)) wt1 = (tim(3)-tim(2))/(tim(3)-tim(1))
        wt1 = max(0., min(1., wt1))
        wt3 = 1. - wt1
        dat(2) = dat(1)*wt1 + dat(3)*wt3
      endif

      aggfor = dat(2)

      return
      end