Sankey diagram

R code of the ggplot2 example

library(ggplot2)
library(dplyr)
library(ggsankey)  # on GitHub only: pak::pak("davidsjoberg/ggsankey")

## The global carbon budget, mean of 2015-2024 (GtC per year), from the
## Global Carbon Budget 2025: what is emitted, then where it goes. Fossil
## emissions include the cement carbonation sink; the budget imbalance,
## under 0.1 GtC, is left out.
sources <- c(`Fossil fuels and industry` = 9.8, `Land-use change` = 1.4)
sinks <- c(Atmosphere = 5.6, Ocean = 3.2, Land = 2.4)
## One row per tenth of a gigatonne: the quantity is conserved from one
## stage to the next, and every row passes through the total.
carbon <- tibble(source = rep(names(sources), round(10 * sources)),
                 total = "Total emissions",
                 sink = rep(names(sinks), round(10 * sinks)))
values <- c(sources, `Total emissions` = sum(sources), sinks)
flows <- make_long(carbon, source, total, sink) |>
  mutate(label = paste0(node, " (", sprintf("%.1f", values[node]), ")"))

p <- ggplot(flows, aes(x = x, next_x = next_x, node = node, next_node = next_node,
                       fill = node, label = label)) +
  geom_sankey(flow.alpha = 0.5, node.color = NA, width = 0.08, space = 6) +
  geom_sankey_text(hjust = -0.12, space = 6, size = 2.8, colour = "#262626") +
  scale_fill_manual(values = c(`Fossil fuels and industry` = "#9b2367", `Land-use change` = "#dc863b",
                               `Total emissions` = "#535353", Atmosphere = "#a6a6a6",
                               Ocean = "#2e7891", Land = "#7a9132")) +
  scale_x_discrete(labels = c(source = "Emitted by", total = "", sink = "Taken up by"),
                   position = "top", expand = expansion(add = c(0.3, 0.6))) +
  labs(title = "Half of the carbon emitted stays in the atmosphere",
       subtitle = "Carbon budget, 2015–2024 mean, in gigatons of carbon per year",
       x = NULL, y = NULL,
       caption = "Data: Global Carbon Budget 2025 (Friedlingstein et al. 2026, CC BY 4.0)") +
  theme_lex_viz(grid = "", arrows = "") +
  theme(legend.position = "none", axis.text.y = element_blank())