AE 09: Telling a story of CO₂ emissions over time

Application exercise
Modified

February 25, 2025

Note

This application exercise is completed in class and submitted via a worksheet.

library(tidyverse)

Data

The dataset comes from the World Bank and contains information on CO₂ emissions, GDP per capita, and population for 215 countries from 1995 to 2022. The data is available in the file wdi_co2.csv. We will import the data and perform some basic cleaning tasks.

# import raw data obtained using WDI API
wdi_co2_raw <- read_csv("data/wdi_co2.csv")

# clean the data
wdi_clean <- wdi_co2_raw |>
  # remove observations that are not actually countries
  filter(region != "Aggregates") |>
  # select relevant columns and rename to make it easier
  select(iso2c, iso3c, country, year,
    population = SP.POP.TOTL,
    co2_emissions = EN.ATM.CO2E.PC,
    gdp_per_cap = NY.GDP.PCAP.KD,
    region, income
  )

wdi_clean
# A tibble: 6,020 × 9
   iso2c iso3c country   year population co2_emissions gdp_per_cap region income
   <chr> <chr> <chr>    <dbl>      <dbl>         <dbl>       <dbl> <chr>  <chr> 
 1 AF    AFG   Afghani…  2001   19688632        0.0553         NA  South… Low i…
 2 AF    AFG   Afghani…  1998   18493132        0.0713         NA  South… Low i…
 3 AF    AFG   Afghani…  2009   27385307        0.240         490. South… Low i…
 4 AF    AFG   Afghani…  2000   19542982        0.0552         NA  South… Low i…
 5 AF    AFG   Afghani…  2012   30466479        0.335         571. South… Low i…
 6 AF    AFG   Afghani…  1996   17106595        0.0823         NA  South… Low i…
 7 AF    AFG   Afghani…  1999   19262847        0.0582         NA  South… Low i…
 8 AF    AFG   Afghani…  2002   21000256        0.0668        344. South… Low i…
 9 AF    AFG   Afghani…  2003   22645130        0.0730        347. South… Low i…
10 AF    AFG   Afghani…  2004   23553551        0.0549        339. South… Low i…
# ℹ 6,010 more rows

Next we rank countries based on their CO₂ emissions in 1995 and 2020, and then calculate the difference in rankings. We also create a variable that indicates if the rank changed by a lot (more than 30 positions). This requires substantial data cleaning and wrangling.

co2_rankings <- wdi_clean |>
  # Get rid of smaller countries
  filter(population > 200000) |>
  # Only look at two years
  filter(year %in% c(1995, 2020)) |>
  # Get rid of all the rows that have missing values in co2_emissions
  drop_na(co2_emissions) |>
  # Look at each year individually and rank countries based on their emissions that year
  mutate(
    ranking = rank(co2_emissions),
    .by = year
  ) |>
  # Only select required columns
  select(iso3c, country, year, region, income, ranking) |>
  # pivot long
  pivot_wider(names_from = year, names_prefix = "rank_", values_from = ranking) |>
  # Find the difference in ranking between 2020 and 1995
  mutate(rank_diff = rank_2020 - rank_1995) |>
  # Remove all rows where there's a missing value in the rank_diff column
  drop_na(rank_diff) |>
  # Make an indicator variable that is true of the absolute value of the
  # difference in rankings is greater than 30
  mutate(big_change = if_else(abs(rank_diff) >= 30, TRUE, FALSE)) |>
  # Make another indicator variable that indicates if the rank improved by a
  # lot, worsened by a lot, or didn't change much.
  mutate(better_big_change = case_when(
    rank_diff <= -30 ~ "Rank improved",
    rank_diff >= 30 ~ "Rank worsened",
    .default = "Rank changed a little"
  )) |>
  # arrange rows by rank_diff for printing
  arrange(rank_diff)

Here is what the data looked like originally:

slice_head(wdi_clean, n = 5)
# A tibble: 5 × 9
  iso2c iso3c country    year population co2_emissions gdp_per_cap region income
  <chr> <chr> <chr>     <dbl>      <dbl>         <dbl>       <dbl> <chr>  <chr> 
1 AF    AFG   Afghanis…  2001   19688632        0.0553         NA  South… Low i…
2 AF    AFG   Afghanis…  1998   18493132        0.0713         NA  South… Low i…
3 AF    AFG   Afghanis…  2009   27385307        0.240         490. South… Low i…
4 AF    AFG   Afghanis…  2000   19542982        0.0552         NA  South… Low i…
5 AF    AFG   Afghanis…  2012   30466479        0.335         571. South… Low i…

And here is what it looks like after cleaning:

slice_head(co2_rankings, n = 5)
# A tibble: 5 × 9
  iso3c country           region income rank_1995 rank_2020 rank_diff big_change
  <chr> <chr>             <chr>  <chr>      <dbl>     <dbl>     <dbl> <lgl>     
1 ZWE   Zimbabwe          Sub-S… Lower…        75        39       -36 TRUE      
2 DNK   Denmark           Europ… High …       160       127       -33 TRUE      
3 SWE   Sweden            Europ… High …       132       100       -32 TRUE      
4 SYR   Syrian Arab Repu… Middl… Low i…        96        64       -32 TRUE      
5 MLT   Malta             Middl… High …       128        99       -29 FALSE     
# ℹ 1 more variable: better_big_change <chr>

Basic plot

Let’s create a basic plot that visualizes the changes in CO₂ emission rankings between 1995 and 2020.

Brainstorm improvements

Your turn: Brainstorm methods to improve the readability and interpretability of the chart through annotations.

Points to emphasize

  • What is a “good” rank? What is a “bad” rank?

    Note
    • 1 is lowest carbon emissions per capita
    • 170 is the highest carbon emissions per capita

  • What are the countries that have significantly improved or worsened their rank?

  • What other aspects do you feel should be emphasized?

Methods for annotation

  • Text labels
  • Arrows/lines
  • Rectangles
  • Colors/fills

Acknowledgments