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Changing Energy outlines how humanity came to its current energy economy through three previous energy transitions and now stands poised for a necessary fourth one. Despite the immense benefits conferred by a global energy economy based primarily on coal, oil, gas, and uranium, societies must now rebuild their energy economies to rely as much as possible on renewable energy used efficiently. This imperative to change comes from the risks of climate change plus the dangers of geopolitical tensions, health and environmental effects, and the long-term prospects for ever depleting sources of today’s energy sources. Changing Energy argues that sustainability of the benefits from energy services will come from investments made in the technologies of the fourth transition. Perkins envisions a viable post–fossil fuel energy economy and outlines the barriers that must be resolved to reach it.

The Keystone State, so nicknamed because it was geographically situated in the middle of the thirteen original colonies and played a crucial role in the founding of the United States, has remained at the heart of American history. Created partly as a safe haven for people from all walks of life, Pennsylvania is today the home of diverse cultures, religions, ethnic groups, social classes, and occupations. Many ideas, institutions, and interests that were formed or tested in Pennsylvania spread across America and beyond, and continue to inform American culture, society, and politics. Pennsylvania: A History of the Commonwealth is the first comprehensive history of the Keystone State in almost three decades. In it distinguished scholars view Pennsylvania's history critically and honestly, setting the Commonwealth's story in the larger context of national social, cultural, economic, and political development. Part I offers a narrative history and Part II offers a series of "Ways to Pennsylvania's Past" -- nine concise guides designed to enable readers to discover Pennsylvania's heritage for themselves. Pennsylvania: A History of the Commonwealth is the result of a unique collaboration between The Pennsylvania State University Press and The Pennsylvania Historical and Museum Commission (PHMC), the official history agency of the Commonwealth of Pennsylvania. The result is a remarkable account of how Pennsylvanians have lived, worked, and played through the centuries.