This visualization shows the average atmospheric CO2 concentration at Mauna Loa Observatory for each year, plotted as a filled line chart. The chart displays the data on a Cartesian coordinate system using the Chart.js library, with years on the x-axis and CO2 concentration in parts per million (ppm) on the y-axis. The server, built with Express, parses the provided CSV file via the `fs` and `path` modules, calculates annual averages from the monthly readings, and exposes the processed data through a `/api/co2-data` endpoint. The frontend fetches this JSON data and renders the chart on an HTML canvas element. The underlying data originates from the Scripps CO2 Program's in situ air measurements.