Mitchell, Democrat from Maine and Senate Majority Leader, heads the Senate Committee on Environmental Protection, fought for years for legislation on acid rain, and led the Senate struggle for a meaningful new Clean Air Act against Administration concerns about the costs to industry. Here, in a punchy and somewhat primerish presentation, he succinctly summarizes the environmental challenge before us--the ""Four Horsemen"" of acid rain, global warming, depletion of the ozone layer, and desertification, and the ""Fifth Horseman"" of Third World population growth--and makes an urgent plea for action before it is too late. As might be expected from his own position in government, Mitchell's solutions are on the order of official national and international task forces, measures, and priorities. Specific measures focus on energy efficiency and conservation, and are quite conservative themselves--better car mileage, for example, but no word about mass raft transportation. Mitchell recognizes the difficulties of changing entrenched habits and especially deplores what he sees as the Reagan hostility to the environment and Bush's failure to support his pro-environment claims, but is deliberately optimistic about the possibility of saving the planet. Mitchell's rousing call to action could reach an audience impatient with more technical discussions, reinforce the current popular concern, and serve as motivating orientation for student work.