This example visualizes monthly global land-surface temperature anomalies from 1753 to 2015, using a heatmap of red rectangles over an SVG. It relies on React and D3 v7 (via `json`, `scaleLinear`, and `scaleBand`) to render axes, tooltips, and color opacity based on temperature variance. The data comes from the freeCodeCamp global-temperature JSON file. Hovering over a bar displays the year, month, actual temperature, and variance using a positioned tooltip.