Mauna Loa CO₂ polar plot

After a classic plot of the Keeling curve (see our former post) used on Wikipedia, we can explore another data visualization. The CO₂ atmospheric concentration, the main cause of the climate warming, is following a seasonal cycle so it could be interesting (or ironic?) to use a polar plot.

60 years of CO₂ increase

Config and data

We only keep two translations for brevity here…

# Polar plot of Mauna Loa CO2 concentration since 1958
# http://r.iresmi.net/2020/01/01/mauna-loa-co2-polar-plot/

# Required packages
library(dplyr)
library(readr)
library(ggplot2)
library(scales)
library(lubridate)


# Translations ------------------------------------------------------------

language <- list(
  en_US = list(
    locale_lc_time = "en_US.UTF-8",
    title = bquote("Monthly mean"~CO[2]~"concentration"),
    caption = paste("Data : P. Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/)\nand R. Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/). Accessed", Sys.Date()),
    x = "Year",
    y = bquote(CO[2]~"fraction in dry air ("*mu*"mol/mol)"),
    x2 = "Month",
    y2 = bquote(atop(CO[2]~"fraction in dry air ("*mu*"mol/mol)", "Departure from yearly average")),
    title2 = "Seasonal variation"
  ),
  fr_FR = list(
    locale_lc_time = "fr_FR.UTF-8",
    title = bquote("Moyenne mensuelle de la concentration de"~CO[2]),
    caption = paste("données : P. Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/)\net R. Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/). Accédé le", Sys.Date()),
    x = "année",
    y = bquote("fraction de"~CO[2]~"dans l'air sec ("*mu*"mol/mol)"),
    x2 = "mois",
    y2 = bquote(atop("fraction de"~CO[2]~"dans l'air sec ("*mu*"mol/mol)", "en écart à la moyenne annuelle")),
    title2 = "Variation saisonnière"
  ))


# Data --------------------------------------------------------------------

# https://www.esrl.noaa.gov/gmd/ccgg/trends/
co2ml <- read_table(
  "ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_mm_mlo.txt",
  col_names = c("year", "month", "decimal", "average", "deseason", "ndays", "stddays", "unc"),
  col_types = "iidddidd",
  na = c("-99.99", "-1"),
  comment = "#") %>% 
  group_by(year) %>% 
  mutate(year_mean = mean(average, na.rm = TRUE),
         delta = average - year_mean,
         vdate = ymd(paste0("2015-", month, "-01"))) %>% 
  ungroup() %>% 
  rename(co2 = average) 

Create the plot for each language and save

We use a virtual date to keep the data in the same January-December interval and we add a partial dataframe to smooth the Dec./Jan. transition and build the spiral.#| fig-cap: 60 years of CO₂ increase

# Polar plot --------------------------------------------------------------

for (l in names(language)) {
  message(l)
  current <- language[[l]]
  
  # format the date in local names
  Sys.setlocale("LC_TIME", current$locale_lc_time)
  
  co2ml %>% 
    filter(vdate == "2015-01-01") %>% 
    mutate(vdate = ymd("2015-12-31"),
           year = year - 1) %>% 
    bind_rows(co2ml) %>% 
    ggplot(aes(vdate, co2, group = year, color = year)) +
    geom_line(size = 1.2) +
    scale_x_date(breaks = pretty_breaks(12), labels = date_format("%b")) +
    scale_color_viridis_c() +
    labs(subtitle = current$title,
         x = "",
         y = current$y,
         color = current$x,
         title = paste("Mauna Loa", min(co2ml$year), "-", max(co2ml$year)),
         caption = paste0("http://r.iresmi.net/\n", current$caption)) +
    coord_polar() +
    theme_bw() +
    theme(axis.title.y = element_text(hjust = .85),
          panel.grid.major.y  = element_blank(),
          panel.grid.minor.x = element_blank(),
          panel.border = element_blank(),
          plot.caption = element_text(size = 7))
  
  ggsave(file = paste("co2_mauna_loa_polar", l, Sys.Date(), "wp.svg", sep = "_"), 
         width = 20, 
         height = 20, 
         units = "cm", 
         device = svg)
}

Does this new year look good? Will the spiral cross its path one day?

Last version of the code on Gitlab.