Book excerpt: The climate change reckoning looms. As scientists try to discern what the Earth’s changing weather patterns mean for our future, Rachel Rothschild seeks to understand the current scientific and political debates surrounding the environment through the history of another global environmental threat: acid rain. The identification of acid rain in the 1960s changed scientific and popular understanding of fossil fuel pollution’s potential to cause regional—and even global—environmental harms. It showed scientists that the problem of fossil fuel pollution was one that crossed borders—it could travel across vast stretches of the earth’s atmosphere to impact ecosystems around the world. This unprecedented transnational reach prompted governments, for the first time, to confront the need to cooperate on pollution policies, transforming environmental science and diplomacy. Studies of acid rain and other pollutants brought about a reimagining of how to investigate the natural world as a complete entity, and the responses of policy makers, scientists, and the public set the stage for how societies have approached other prominent environmental dangers on a global scale, most notably climate change. Grounded in archival research spanning eight countries and five languages, as well as interviews with leading scientists from both government and industry, Poisonous Skies is the first book to examine the history of acid rain in an international context. By delving deep into our environmental past, Rothschild hopes to inform its future, showing us how much is at stake for the natural world as well as what we risk—and have already risked—by not acting.