Alcamo received a Bachelor's degree in civil engineering and a Master's degree in environmental engineering from Manhattan College, and earned his PhD for civil-environmental engineering at the University of California. From 1973 to 1980, he worked as en environmental engineer in the private sector, before changing to the Lawrence Berkeley National Laboratory in 1981 and fro there to the International Institute for Applied Systems Analysis in Austria in 1982. From 1992 to 1996, Alcamo worked at the Netherlands National Institute for Public Health and the Environment. Since 1996, Alcamo is a professor at Kassel University in Germany, working as the head of the university's Center for Environmental Systems Research. He has taken a temporary leave of absence from the institute, however, to work as the Chief Scientist for UNEP.
In 1998, Alcamo was awarded the Max Planck Research Prize for physics and geoscience, in honor of his contributions to global modeling, and the use of global models in international policy.