1. 1Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA; email: dbloom@hsph.harvard.edu
2. 3Wittgenstein Centre for Demography and Global Human Capital, Vienna, Austria
3. 2Economic Frontiers Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria; email: kuhn@iiasa.ac.at
4. 4Department of Economics, Vienna University of Economics and Business, Vienna, Austria; email: klaus.prettner@wu.ac.at