Electronic textbooks, often lauded as a cheaper alternative to hard copies, may also seem like a perfect way for colleges to reduce their greenhouse-gas emissions. Many institutions encourage use of e-books, and one state, California, has required that all textbooks used in college classes be made available electronically by 2020. In a sign of growing campus interest in cutting carbon emissions, nearly 700 institutions have signed the American College & University Presidents' Climate Commitment, pledging to reduce their footprint and to promote education and research on climate change.