In terms of geographic breadth, Larsson's proposal, which he submitted as a final-year project while studying at London's Architectural Association, is roughly on scale with the Green Wall of the Sahara, a 23-nation initiative already under way, to contain the spreading desert with a nine-mile-thick barrier of trees extending along the same stretch that Larsson is eyeing. In fact, Larsson sees his project as supporting the Green Wall, literally. His hardened sand wall—up to 1,000 feet deep in some places—would provide a more stable base for the trees, with full-scale homes carved out of the dunes. In his drawings, the dwellings look like millions of row houses with green roofs keeping the desert at bay. Solidification, Larsson maintains, would pose few risks to the environment or human health, since it relies on harmless microbes naturally present in marshes and wetlands. The U.C. Davis method simply spurs the microbes to excrete extra calcium carbonate, bonding the sand together tightly like cement.