This visualization displays global surface temperature changes since the 1700s using a heatmap of monthly temperature variances. Each cell represents a year and month, colored on a gradient from mint to dark red based on temperature deviation from a baseline. The code loads data from a JSON file via `d3.json`, renders SVG rectangles with scales created using `d3.scale.linear`, and includes interactive tooltips. The visualization also incorporates D3 axes, a time scale for month labels, and computed color thresholds for temperature ranges.