The amount of CO₂ in the air can be measured. The National Oceanic and Atmospheric Administration (NOAA) department has been collecting data on the amount of CO₂ in the air since the early 1950s. The data we'll be using can be found at https://www.esrl.noaa.gov/gmd/ccgg/trends/data.html. We'll specifically be using that Mauna Loa monthly mean data.

The data, after removing the comments, looks something like this:

# decimal average interpolated trend #days
# date (season corr)
1958 3 1958.208 315.71 315.71 314.62 -1
1958 4 1958.292 317.45 317.45 315.29 -1
1958 5 1958.375 317.50 317.50 314.71 -1
1958 6 1958.458 -99.99 317.10 314.85 -1
1958 7 1958.542 315.86 315.86 314.98 -1
1958 8 1958.625 314.93 314.93 315.94 -1

In particular, we are interested in the interpolated column.

Because this is a particularly interesting dataset, it might be worth looking at how to download and preprocess the data directly in Go.