William Ripple and Christopher Wolf are affiliate with the Dept. of Forest Ecosystems and Society at Oregon State University,Thomas M. Newsome is affiliated with the School of Life and Environmental Sciences at The University of Sydney,. Phoebe Barnard is affiliated with the Conservation Biology Institute, in Corvallis, Oregon, William R. Moomaw is affiliated with The Fletcher School and the Global Development and Environment Institute, at Tufts University: The world must quickly implement massive energy conservation practices and must replace fossil fuels with low-carbon renewables. We should leave remaining stocks of fossil fuels in the ground. Still increasing by roughly 80 million people per year, the world population must be stabilized—and, ideally, gradually reduced. There are proven and effective policies that lower fertility rates and lessen the impacts of population growth on GHG emissions.