R/co2_20ma.R

In andreas50/utsData: Example Data Sets of Unevenly Spaced Time Series

#' 20 Million Year Atmospheric CO2 Reconstruction
#' 
#' This function creates the \code{\link{co2_20ma}} dataset by downloading the data from a website by the \href{https://www.ncdc.noaa.gov/paleo/study/10423}{NOAA Earth System Research Laboratory} and returning it as a \code{\link[uts]{uts}} object. It is not meant to be called directly, but provided for reproducability.
#'
#' @keywords datasets internal
#' @examples 
#' co2_20ma <- download_co2_20ma()
#' 
#' # Save the data
#' \dontrun{
#'   save(co2_20ma, file=file.path("data", "co2_20ma.rda"), compress="xz")
#' }
download_co2_20ma <- function()
{
  # Download data into temporary file
  file <- "http://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2009/tripati2009.txt"
  message("Downloading the Atmospheric CO2 20 Million Year Reconstruction data from ", file)
  message("Please see www.ncdc.noaa.gov/paleo/study/10423 for a detailed description.")
  tmp_file <- tempfile()
  on.exit(unlink(tmp_file))
  download.file(file, destfile=tmp_file, quiet=TRUE)
  
  # Import data
  data <- scan(tmp_file, what="character", quiet=TRUE, sep="\n")
  start_pos <- grep("pCO2avg", data, fixed=TRUE) + 1
  data <- data[start_pos:length(data)]
  
  # Clean data
  age_ma <- as.numeric(substr(data, 1, 5))
  CO2 <- as.numeric(substr(data, 14, 16))
  
  # Sort data chronologically
  pos <- order(age_ma, decreasing=TRUE)
  age_ma <- age_ma[pos]
  CO2 <- CO2[pos]
  
  # Determine observation times
  # -) need to generate indirectly, because strptime(), which is used by ISOdate(), only accepts years 0:9999 as input
  times <- as.POSIXlt(ISOdate(2000, month=1, day=1, hour=0) + dyears(rep(0, length(age_ma))))
  times$year <- times$year - age_ma * 1e6
  times <- as.POSIXct(times)
  
  # Return "uts" object
  uts(CO2, times)
}


#' 20 Million Year Atmospheric CO2 Reconstruction
#'
#' A 20 million year (ma) reconstruction of the atmposheric CO2 concentration (in parts per million).
#'
#' @format A \code{\link[uts]{uts}} object.
#'
#' @source This dataset was imported by \code{\link{download_co2_20ma}} in January 2016 from a website by the \href{https://www.ncdc.noaa.gov/paleo/study/10423}{NOAA Earth System Research Laboratory}.
#' @source Tripati, A.K., C.D. Roberts, and R.A. Eagle. 2009. Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years. Science, Vol. 326, pp. 1394-1397, 4 December 2009. DOI: 10.1126/science.1178296
#'
#' @seealso \code{\link{co2_ml}} for monthly data since 1958.
#' @seealso \code{\link{co2}} in base \R.
#' 
#' @name co2_20ma
#' @keywords datasets
#' @examples
#' data(co2_20ma)
#' plot(co2_20ma, max_dt=dyears(1e6), type="o")      # connect observations less than 1 ma apart
#' plot(tail_t(co2_20ma, dyears(1.5e6)),  type="o")  # plot the 1.5 million most recent years
NULL