This International Environmental Olympiad issue builds contest-ready understanding of human activity as an environmental force. It connects cities, energy systems, material flows, lifecycle assessment, urban heat, e-waste, energy charts, waste audits, transit data, Singapore, Copenhagen, river plastics, nuclear power, renewable siting, plastic bans, batteries, green buildings, AI infrastructure, recycling, hydrogen cars, and smart cities. The emphasis is systems reasoning: where impacts originate, how they move through infrastructure and supply chains, and what evidence separates real solutions from attractive labels.