Calculates the radiative forcing in W m-2 based on changes in CO2 concentration #' using the formula from Myrhe et al. (1998).

radiative_forcing.r

#' Calculate Radiative Forcing from CO2 Concentration
#'
#' Calculates the radiative forcing in W m-2 based on changes in CO2 concentration
#' using the formula from Myrhe et al. (1998).
#'
#' The radiative forcing is calculated using the equation:
#' \deqn{\Delta F = 5.35 \times \ln(C/C_0)}{ΔF = 5.35 * ln(C/C0)}
#'
#' @param C numeric vector. Current CO2 concentration in ppm.
#' @param C0 numeric. Reference CO2 concentration in ppm. Default is 280 ppm
#'   (pre-industrial level). Can be a single value or vector of same length as C.
#'
#' @return numeric vector. Radiative forcing in W m-2.
#'
#' @details
#' The function is vectorized and works with multiple CO2 values.
#' All input values must be positive.
#'
#' @references
#' Myrhe, G., Highwood, E. J., Shine, K. P., & Stordal, F. (1998).
#' New estimates of radiative forcing due to well mixed greenhouse gases.
#' \emph{Geophysical Research Letters}, 25(14), 2715-2718.
#' \doi{10.1029/98GL01908}
#'
#' @examples
#' # Current CO2 levels (420 ppm) vs pre-industrial (280 ppm)
#' radiative_forcing(420, C0 = 280)
#'
#' # Doubled CO2 concentration
#' radiative_forcing(560, C0 = 280)
#'
#' # Multiple CO2 levels (vectorized)
#' radiative_forcing(c(350, 400, 450, 500, 550), C0 = 280)
#'
#' @export
radiative_forcing <- function(C, C0 = 280) {
  
  # Input validation
  if (!is.numeric(C) || !is.numeric(C0)) {
    stop("C and C0 must be numeric values")
  }
  
  if (any(C0 <= 0) || any(C <= 0)) {
    stop("C and C0 must be positive values")
  }
  
  # Calculate radiative forcing using Myrhe et al. (1998) formula
  delta_F <- 5.35 * log(C / C0)
  
  return(delta_F)
}