Sources: Zeke Hausfather, The Climate Brink (eight weeks of Claude Code use, 1,138 prompts, 14,000+ model calls, 3.2 billion tokens); Bistline et al., Watershed white paper 2026 (agentic workflow range); Google and OpenAI published per-prompt figures for chat. Watt-hours are data-centre electricity; ranges reflect methodology uncertainty, not measurement error.