Dr. Declet-Barreto began his career as an Emissions Inventory Specialist at the Arizona Department of Environmental Quality in 2007, where he developed ambient air emissions inventories using geospatial and tabular data to support air quality regulations. In this role, he also liaised between local and regional authorities in the U.S. and Mexico to obtain air quality data for air quality studies. He continued his service at the local level with the City of Mesa as a GIS Specialist from 2011 to 2014, in which he used ModelBuilder, Python, and Spatial ETL tools for land base migration from CAD to Geodatabase format and served as the GIS Specialist for City during Emergency Operations Center activations.

Dr. Declet-Barreto continued to contribute his GIS software and analysis expertise with the Natural Resources Defense Council in Washington, D.C., where he served as a Climate Health-Science Center Fellow and a Climate Vulnerability Consultant from 2014-2016. In these roles, he developed vulnerability assessments to help increase resilience, particularly in infrastructure, transit, housing, and health. He also helped develop and deliver webinar workshops to help people build policy analysis and visualization skills. These roles highlighted his interdisciplinary background and knowledge, as he combined his technical training in GIS and other applications with social-environmental issues, particularly environmental justice and vulnerable groups.

These experiences led him to his current position as a Senior Social Scientist for Climate Vulnerability at the Union of Concerned Sciences, where he has served since 2017. As a social scientist, Dr. Declet-Barreto partners with environmental justice communities to advance social and environmental justice solutions in the context of climate vulnerability. His work still includes spatial analysis and other analytical tools but is highly community-oriented, highlighting the interdisciplinary work of his doctoral studies and subsequent work experiences.