This interactive heatmap visualizes CO₂ emissions per capita for multiple countries over 2016–2023, with countries as rows and years as columns. Users toggle between an alphabetically ordered matrix and a reordered version sorted by each country’s average emissions, revealing clustering patterns. Built with D3 v7, the SVG visualization uses a sequential YlOrRd color scale (via `d3.scaleSequential` and `d3.interpolateYlOrRd`) applied to the `co2_per_capita` field. Data is loaded from a local CSV file with a GitHub Gist fallback, with rows aggregated using `d3.rollup` and `d3.mean`.