This visualization displays monthly CO2 concentration measurements from the Keeling dataset as a smooth line chart, with years on the x-axis and CO2 concentration in parts per million on the y-axis. It uses d3.csv for data loading, d3.scaleLinear for axis scaling, and d3.line with curveMonotoneX to draw the trend. The SVG rendering includes axis labels, a steelblue stroke, and a loading state. Data is sourced from a GitHub gist containing the Mauna Loa measurements.